A shank fumigation trial was conducted in 2007 at the UC Kearney Agricultural Center , near Parlier, to determine the effect of two fumigation shank types and five soil surface treatments on 1,3-D emissions and control of representative soilborne pests following removal of a plum orchard. Soil texture at the site was a Hanford fine, sandy loam with pH 7.2, 0.7% organic matter, and a composition of 70% sand, 24% silt and 6% clay. The experiment included 10 treatments with 1,3-D in a split plot design with surface treatments as the main plots and two application shank types as the subplots, as well as an unfumigated control and a methyl bromide plus chloropicrin standard for comparison . Individual plots were 12 feet by 100 feet, and each treatment was replicated three times. Fumigant application. Fumigants were applied using commercial equipment on Oct. 2, 2007. Methyl bromide with chloropicrin was applied at 350 pounds per acre with a Noble plow rig set up to inject fumigants 10 inches deep through emitters spaced 12 inches apart while simultaneously installing 1-mil high-density polyethylene film. The 1,3-D treatments, at 332 pounds per acre, were applied using either a standard Telone rig with shanks spaced 20 inches apart and an injection depth of 18 inches or a Buessing shank rig with shanks spaced 24 inches apart and the fumigant injection split at 16- and 26-inch injection depths. The Buessing shank also had wings above each injection nozzle to scrape soil into the shank trace and minimize rapid upward movement of the fumigant . Following 1,3-D application, a disk and ring roller was used to level and compact the surface soil before surface seals were applied over the fumigated plots. Average soil temperature at 20 inches during fumigation was 70°F, grow rack with lights and soil moisture was 8.2% to 10.5% weight per weight in the top 3 feet. Surface treatments included HDPE film; virtually impermeable film, VIF ; and a series of intermittent water applications .

The intermittent water seals treatment was applied using a temporary sprinkler system installed in the plots following fumigation and the post fumigation tillage operation; water was applied four times in the first 2 days after fumigation: 0.5 inch after 3 hours, 0.2 inch after 12 hours, 0.2 inch after 24 hours and 0.2 inch after 48 hours. All plastic films were removed 10 days after fumigation. Fourteen days after the initial 1,3-D fumigation, the metam sodium treatment was applied through sprinklers at 160 pounds per acre in 2.75 inches of water. For the dual application treatment, 21 days after the initial treatment, soil was inverted with a moldboard plow and an additional 1,3-D treatment was applied with the previously described Telone rig and rolling operation. Emissions data collection. Fumigant emissions from eight 1,3-D treatments — two application shank types times four surface seal methods — were monitored in three replicate plots for 10 days following the initial application. Emission of 1,3-D from the soil surface was monitored using previously described dynamic flux chamber techniques . Briefly, a flow-through flux chamber with a 10-inch-by-20-inch opening was installed on the surface following fumigant injection and installation of the films or after the initial water seal treatment . These chambers allow semi-automated, continuous sampling of fumigant concentrations in the air above the surfaces. The cis– and trans-isomers of 1,3-D were trapped in charcoal sampling tubes . The two 1,3-D isomers were summed as total 1,3-D for data analysis and reporting. Individual tubes were removed from the flux chambers every 3 to 6 hours and stored frozen until laboratory processing. Emission flux and cumulative emission during the 10-day monitoring period were calculated based on surface area and air flow rates through the flux chambers, and treatment differences were compared using analysis of variance . The concentration of 1,3-D in the soil-gas phase was determined 6, 12, 24, 48, 120 and 240 hours after treatment. At each time point, samples were collected using a multiport sampling probe and a system of gas-tight syringes to draw air from eight depths through charcoal sampling tubes. Samples were stored frozen until analysis. In the laboratory, all samples were processed using procedures described by Gao et al. . Briefly, sample tubes were broken and trapped fumigants were extracted from the trapping matrix with ethyl acetate and analyzed using a gas chromatograph equipped with a micro electron capture detector .

Pest control data collection. Pest control efficacy was evaluated using citrus nematode bioassay counts, fungal dilution plating, and weed emergence counts and biomass collections from each replicated plot. The pest control data from this research station emission flux experiment were reported in Jhala et al. . Rose and tree nursery trials In addition to the emission flux and efficacy study conducted at KAC, two field trials were conducted in commercial nurseries to evaluate pest control efficacy and nursery stock productivity. Fumigation and surface treatments in the nursery experiments were the same as in the flux study with minor exceptions . The commercial nursery trials were arranged as randomized complete block experiments with a split plot arrangement of 1,3-D treatments. The whole plot factor was surface treatment, and the split plot factor was the shank type. Individual plots in these experiments were 22 feet by 90 feet, and each treatment was replicated four times. Fumigant application. In 2007, the experiment was established in a garden rose nursery near Wasco. The soil at the rose nursery site was a McFarland loam with pH 6.2, 0.9% organic matter and 74% sand, 13% silt and 13% clay. Treatments were applied on Nov. 7, 2007, when the soil temperature was 64ºF and soil moisture averaged 9.2% w/w from 2 to 5 feet. The experiment was repeated in 2008 in a deciduous tree nursery near Hickman, in a Whitney and Rocklin sandy loam soil with pH 6.5, 0.8% organic matter, and 66% sand, 23% silt and 11% clay. Treatments in the tree nursery trial were applied on Aug. 13, 2008, when the soil was 80ºF and soil moisture ranged from 5.0% to 12.6% w/w in the top 5 feet. Immediately following 1,3-D application, a disk and roller were used to compact the soil and disrupt shank traces and HDPE and VIF were installed using the Noble plow rig. For the water seal main plots, a temporary sprinkler system was installed after the post fumigation tillage operation and intermittent water seals were applied: 0.5 inch after 3 hours, and 0.2 inch each after 12, 24 and 48 hours.

The dual application 1,3-D treatments were applied in the garden rose experiment on Nov. 28, 2007, but were not included in the 2008 tree nursery experiment. Metam sodium was applied in 2.75 inches of irrigation water through sprinklers 14 to 30 days after the initial 1,3-D treatment in both experiments. All plastic films were removed 2 to 3 weeks after fumigation at both sites. Crop production and data collection. Both nursery trials were managed by the cooperating growers using their standard practices for planting, fertilization, in-season tillage and budding and harvest operations. In the 2007 rose experiment, two rows each of the rose rootstock ‘Dr. Huey’ and the own-rooted garden rose variety ‘Home Run’ were planted as hardwood cuttings in December 2007. Rose nursery stock was planted 7 inches apart in furrows spaced 3 feet apart, and the field was furrow irrigated during the 2008 and 2009 growing seasons. The own-rooted cultivar was harvested after one growing season in January 2009, and the unbudded ‘Dr. Huey’ rootstock was harvested in February 2010 after an additional growing season. At both harvest dates, all plants in one 90-foot row were lifted using a singlerow undercutting digger, plants were bundled and tagged by plot, and graded in a commercial packinghouse. In the 2008 tree nursery trial, two rows each of the peach rootstock ‘Nemaguard’ and the plum rootstock ‘Myro 29C’ were planted with 8 inches between plants and 5 feet between rows in December 2008. The tree nursery plots were sprinkler irrigated during the 2009 growing season. Due to the market needs of the cooperating nursery, the rootstocks in the tree trial were not available for harvest and grading as a part of the experiment. Pest control efficacy and crop productivity were evaluated during the 12- or 26-month nursery production cycle. Nematode control was determined using a citrus nematode bio-assay in which two sets of muslin bags containing 100 grams of soil infested with citrus nematode were buried at 6, 12, 24 and 36 inches below the soil surface in each plot prior to fumigation. The initial population of citrus nematodes in infested soil was 4,086 and 3,876 nematodes per 100 cubic centimeters of soil in 2007 and 2008, respectively. The bags were recovered 1 month after fumigation, nematodes were extracted from 100 cubic centimeters of soil using the Baermann funnel protocol, indoor grow rack and surviving nematodes were identified and counted. To evaluate the effect of fumigation treatments on soil fungal populations, ten 1-inch-by-12-inch soil cores were collected from each subplot 2 weeks after fumigation. Soils were homogenized, and a subsample was assayed for Fusarium oxysporum Schlecht. and Pythium species using dilution plating techniques on selective media. Pythium species samples were plated on P5ARP medium for 48 hours, and F. oxysporum samples were plated on Komada’s medium for 6 days. Emerged weeds in a 1-square-meter area were identified and counted twice in the winter following the fall fumigation and several times during the subsequent summer growing season. Nursery stock establishment, vigor and growth were monitored during the season. Visual evaluations of crop vigor were made on a scale of 1 to 7, where 7 was the most vigorous and 1 was dead or dying plants. Near the end of the growing season, trunk diameter of 10 plants in each subplot was measured 3 inches above the soil surface using a dial caliper. As previously described, rose nursery stock was harvested and graded to commercial standards ratings, but tree nursery stock was not harvested as a part of the experiment. Data were subjected to analysis of variance, and initial analyses indicated that the shank types did not differ in their effect on any of the pest control or crop growth parameters measured. Thus, data from the two shank type treatments were grouped together within surface treatments and reanalyzed with seven treatments and six treatments . The nematode, pathogen and weed density data were transformed [ln ] to stabilize the variance prior to analysis; however, means of untransformed data are presented for clarity. Treatment means were separated using Fisher’s protected least significant difference procedure with α = 0.05.Emission flux. Within a surface treatment, there were no statistical differences in emission flux between the two application shank types, thus data were combined over application rig. However, significant differences in 1,3-D emission flux were observed among surface treatments . Fumigant emission flux from bare plots was two times higher than from water seals and HDPE and nearly 15 times higher than from VIF within 48 hours after treatment. Emission from water-sealed plots was reduced during the sequential water applications, but flux was similar to bare soil plots after 48 hours. HDPE film continued to give lower emission rates than the bare soil and water seals but was significantly higher than VIF. Throughout the monitoring period, VIF-covered plots had the lowest 1,3-D emissions; maximum flux was 11 micrograms per square meter per second , which was at least 90% lower than that from the bare soil plots. Relative to the bare soil treatment, estimated cumulative 1,3-D emission losses for water seals, HDPE and VIF were 73%, 45% and 6%, respectively, which were similar to reports from a previous field study . Headspace 1,3-D concentration. Concentration of 1,3-D immediately below the plastic film indicated that 1,3-D retention is much greater under VIF film than under HDPE . Several other studies have shown that VIF can retain substantially higher fumigant concentrations without negatively affecting nematode, pathogen and weed control efficacy or crop yield . Fumigant distribution in soil. Initial analysis of fumigant distribution in the surface 90 centimeters indicated that there were no differences between the application shanks within a surface treatment in this zone; thus data were combined over application shank types . The 1,3-D concentration was highest near the injection depth, at 45 centimeters and lowest near the soil surface, at 5 centimeters , and at 90 centimeters , but this difference diminished over time.

Plots that had been planted with field peas and vetches in mid-summer were associated with lower flag leaf nitrogen than plots that had received spring plantings of field peas and vetches. Grass cover crops were associated with the lowest leaf nitrogen, suggesting that the ability of grass decomposition to tie up nitrogen can be persistent. Visual growth differences were apparent throughout the winter wheat growing season; wheat in spring field peas and vetch cover crop treatments were taller and much greener than other treatments. This suggests that nitrogen release from legume cover crops can continue for more than 1 year and can potentially have cumulative effects in crop rotations.Chicken manure amendments were the most effective fall-applied amendments for increasing soil nitrate levels at potato planting . Soil nitrate at potato planting in soil amended with chicken manure was greater than 75 pounds of nitrogen per acre , similar to levels in plots treated with field peas and vetches. Potato petiole nitrate levels for plots amended with chicken manure were over 19,000 ppm at early tuber bulking, similar to levels produced by many field peas and vetches. Potato petiole nitrate at early bulking for blood meal and soy meal amendments was similar to levels associated with both chicken manure and 150 pounds per acre of urea fertilizer . Green waste compost applied at all rates, as well as composted steer manure, led to lower soil nitrate at potato planting than did chicken manure, and these amendments did not increase soil nitrate at potato planting compared to the fallow treatment . Green waste compost and steer manure did not increase potato petiole nitrate at early bulking and vine maturity compared to the fallow treatment, flood drain table suggesting that nitrogen in these amendments mineralized too slowly for a single application to benefit a potato crop .

Potato establishment and early season vigor did not differ significantly among treatments, but differences in potato vigor were significant at row closure and tuber initiation . Treatments producing high potato petiole nitrate produced taller, greener potato plants than did treatments producing low potato petiole nitrate. Russet Norkotah total potato yield, average tuber size and cull yield were influenced by cover crops and amendments while Yukon Gold potato yield was similar for most treatments . This trend was not surprising given that Russet Norkotah is more responsive to nitrogen fertilizer than Yukon Gold. For Russet Norkotah, vetch species , chicken manures, steer manure, blood meal and soil protein fertilizer produced higher total potato yields than did the untreated fallow. These treatments, along with five field pea varieties, resulted in a larger average tuber size than did the untreated fallow . Total yield for the treatment with 150 pounds per acre of urea fertilizer was similar to that produced with vetches, chicken manures and blood meal, suggesting that soil nitrogen availability was a primary factor in increasing potato yield . Nitrogen’s important role is also supported by a strong positive correlation between total Russet Norkotah potato yield and potato petiole nitrate at early bulking. The r value for this correlation equaled 0.656 when Russet Norkotah and Yukon Gold data were combined. The only treatment-related effect on total Yukon Gold potato yield was that cover-cropping with spring wheat and fall triticale produced lower total yield than did cover-cropping with legumes . Grass cover crop treatments led to numerically lower soil nitrogen at planting and lower potato petiole nitrate at early bulking, compared to the untreated fallow .

This suggests that the low potato yield following grass cover crops could be due to nitrogen immobilization during potato growth and development. Cover crop and amendment treatments did not cause a substantial increase in tubers with knobs or growth cracks in either Russet Norkotah or Yukon Gold , but the percentage of cull potatoes based on total yield for Russet Norkotah differed among treatments . Both chicken manure treatments, as well as blood meal and soy protein, resulted in higher percentages of culls than did the untreated fallow. An increase in cull percentage often occurs as total yield increases, but Perfect Organic Blend chicken manure also produced a higher percentage of culls than did the treatment with 150 pounds per acre of urea fertilizer. All cover crop treatments led to a percentage of culls similar to or lower than was associated with the treatment with 150 pounds per acre of urea fertilizer . Yukon Gold was chosen for the 2017 trials because Rhizoctonia black scurf and black dot tuber blemish, common problems for organic potato growers, are easy to see on yellow varieties. The severity of black scurf and black dot did not differ according to cover crop species, but in potatoes grown after spring-planted cover crops , 27% exhibited black scurf — compared to 13% in potatoes grown after mid-summer and fall plantings of cover crops. On the other hand, spring plantings of cover crops led to lower black dot severity on tubers than did mid-summer plantings .Economic issues play a major role in the feasibility of using legume cover crops to boost soil nitrogen in a crop rotation. Organic growers must consider the opportunity cost involved in growing cover crops instead of a cash crop as well as the cost of applying an amendment such as chicken manure. The economic analysis required to weigh all benefits and lost opportunity costs is complex, and beyond the scope of this study, but a comparison of monetary costs shows that cover crop production is more expensive than synthetic fertilizer, similar to applying chicken manure and less expensive than applying blood meal and soy meal.

The average cost of bulk urea fertilizer from local suppliers in Northern California in 2018 was $365 per ton, or $60 to supply one acre with 150 pounds of nitrogen . The average cost of bulk dried poultry manure from local suppliers in Northern California was $145 per ton, or $272 dollars to supply one acre with 150 pounds of nitrogen . The cost of bulk blood meal and soy meal represented a nitrogen cost of greater than $3.40 per pound, or over $500 to supply one acre with 150 pounds of nitrogen. The cost of certified organic blood meal, packaged in 50-pound bags, was greater than $7 per pound of nitrogen, or more than $1,000 to supply one acre with 150 pounds of nitrogen. The total cost of field pea and vetch production is estimated at $175 dollars per acre, including the cost of seed, planting, irrigation, management and incorporation .Vetch, field peas, blood meal, soy meal and chicken manure, because they produced potato yields and potato petiole nitrate similar to those produced in plots treated with 150 pounds per acre of urea fertilizer , were feasible alternatives to synthetic fertilizer. Whether organic producers favor cover crops or chicken manure as a nitrogen source depends on several factors, including land availability and the opportunity to grow cash crops. Producers who grow high-value cash crops requiring a full growing season may favor amendments because they can be quickly applied after harvest or before planting. Producers with idle land or with time between cash crops during the growing season may prefer cover crops, as many legumes in this study added over 150 pounds of nitrogen per acre and provided multi-season carry-over of soil nitrogen, and also offer protection from soil erosion. For hay producers, it’s extremely important to leave above ground biomass from legume cover crops in place, instead of haying the residue, because most added nitrogen is contained in legumes’ leaves and shoots rather than their roots. Regardless, both options offer benefits in soil health, and in our study the added nitrogen in both cases broke down into mineralized form in adequate amounts to meet early-season and late-season potato nitrogen needs. The economic benefit of using cover crops and chicken manure is more difficult to justify in conventional potatoes because, in our research, both practices entail higher costs and greater difficulty of application than synthetic fertilizer, which produced similar yields. For organic potato production, using either grass cover crops or a one-time application of compost to increase soil nitrogen is difficult to justify economically. In our research, grow tables 4×8 these treatments had a neutral or negative effect on soil nitrogen compared to fallow treatments. Organic nitrogen in these treatments failed to convert into mineralized form in adequate amounts to increase either potato yield or yield of wheat planted the year after potatoes. Mustard, arugula and radish had a neutral-to-positive effect on potato yield and nitrogen.

Several Brassica species have also been shown to have biofumigation properties, although a reduction in soilborne potato diseases Rhizoctonia solani, Colletotrichum coccodes and Verticillium wilt was not evident in this study. Fallowing for an entire year, starting in spring the year before growing potatoes, is another option that growers with idle land or limited water can consider. In this research, the spring fallow treatment resulted in mineralized nitrogen at potato planting similar to or higher than levels that resulted from the summer fallow and fall fallow treatments . In potatoes, the spring fallow treatment produced petiole nitrate at early bulking similar to that produced by a treatment with 150 pounds per acre of urea fertilizer following barley . The additional nitrogen in the spring fallow treatment was likely related to natural mineralization of soil organic matter, as organic matter in Tulelake soils is naturally high .Rice is one of the most important sources of human energy worldwide and is grown in a wide range of agroecosystems, though paddy systems are the most prevalent . In California, more than 200,000 ha of flooded rice are grown in a waterseeded, continuously flooded system that has successfully suppressed certain nonaquatic weed species such as barn yard grass [Echinochloa crus-galli Beauv.] and bearded sprangletop . Currently, rice growers in California flood fields at the beginning of the growing season and then direct seed pregerminated rice seed into the flooded fields from airplanes. A flood depth of 10 to 15 cm is maintained until approximately 1 mo before harvest, when the field is drained to allow rice harvesting. Repeated use of flooded irrigation in the California rice agroecosystem has since selected for weed species such as late watergrass [Echinochloa oryzicola Vasinger] that are well adapted to the system. In recent years, California has experienced unprecedented drought, with the 2012 to 2014 period being the driest on record . Accordingly, concerns about water usage have increased, particularly for crops like rice that have high water use. Due to the flood irrigation, rice is a visible water user, receiving attention from both the general public and policy makers, and there is increased pressure on rice growers to reduce water use. In California, the only alternative to water seeding currently in use is dry seeding followed byflooding after early postemergent herbicide applications. Recent research, however, indicates that drill seeding into dry soil as practiced in California rice systems does not necessarily reduce crop evapotranspiration, crop coefficient, or irrigation delivery in comparison with the continuously flooded system . A number of alternatives to flood irrigation exist in other rice-growing regions of the world, including an alternate wet and dry system , which reduces water use over the crop growth period through alternating periods of flooding with periods of drying, and saturated soil culture , which reduces water use over the crop growth period by maintaining the soil at the saturation point . Yields in aerobic systems are often lower due to the reduced ability of rice to compete with weeds , and this may be an obstacle to adoption of alternative irrigation systems by growers. In addition to changing the competitive ability of rice with respect to weeds, alternative irrigation systems can shift weed species composition, selecting for some species over others. In California, differences in irrigation during the seedling recruitment period have been shown to shift the emergence of certain weed species when comparing wet- versus dry-seeded systems . In these systems, water seeding favored sedges and broad leaves, whereas dry seeding favored grasses, particularly watergrass and sprangletop species . Later in the season, sedges and grasses dominate over aquatic weeds in saturated, non-flooded soils . For continuously flooded systems, water depth also affects the presence of certain species. Grasses are suppressed by continuous flooding to a depth of at least 5 cm, whereas a deeper flood of about 15 cm suppresses most sedges .

The recommendations comprehensively address bio-fuel production and use, as well as the necessity of agency and private sector stakeholder cooperation for effective implementation of the recommendations . Initially, all federal agencies with authority relevant to bio-fuel production should be identified, their likely responsibilities on the invasiveness issue determined, and their ability to minimize the risk of bio-fuel escape and invasion strengthened as necessary. To reduce the risk of escape, the bio-fuel crops that are promoted should not be currently invasive or should pose a low risk of becoming invasive in the target region. In addition, bio-fuel crops should be propagated in production sites that are least likely to impact sensitive habitat or create disturbances that would facilitate invasion. Most importantly, effective mitigation protocols need to be developed to prevent dispersal of plant propagules from sites of production, transportation corridors, storage areas and processing facilities. Minimizing harvest disturbance can also reduce the potential for dispersal and off-site movement of propagules. Prior to wide scale planting, multi-year eradication protocols should be developed that are based on integrated pest management strategies. Such practices should be readily available, and appropriate information should be distributed with the purchase of bio-fuel crop seeds. These control methods are not only critical for preventing the dispersal of bio-fuel crops from abandoned production sites, they are a necessary component of an effective early detection and rapid response system for bio-fuel crop populations that do escape active management. Throughout this entire process , flood and drain table all stakeholder groups should be engaged, from bio-fuel development to conversion.The question of how species successfully invade new areas has fascinated scientists for over a century .

By studying ruderal and agricultural weeds invading empty niches, Herbert Baker began to identify characteristics associated with invasiveness, which resulted in a list of traits describing the ‘ideal weed’ . Work in subsequent decades examined a wide range of traits using comparative approaches of taxonomically-related species and regional floras . With these studies came an increasing realization that factors contributing to invasiveness are strongly influenced by the stage of invasion, characteristics of the introduced range, and which species groups are being compared. These realizations, combined with discrepancies across studies, resulted in some skepticism that traits associated with invasiveness could be generalized . However, there is support for the idea that invasive species differ from non-invasive native and non-native species in key attributes depending on the environmental context . Here, we explore how ecological and evolutionary theory has refined our understanding of the ‘ideal weed’. We do not provide an exhaustive review of all traits but rather an overview of key functional and evolutionary frameworks in which progress has been made.Baker’s ‘ideal weed’ possessed a general-purpose phenotype , life history traits that permit reproduction from a single individual , rapid growth, and high, continuous seed output . Several of these characteristics are well studied and appear to be common when evaluated across different invasive taxa such as high germination success across environments , selfing , and rapid growth rate , while others are less studied . In recent decades, researchers have broadened the search for ‘weedy’ characteristics to include traits related to resource acquisition and use that underlie rapid growth, competitive ability, and even stress tolerance. Syntheses of regional and global for as have demonstrated that, relative to non-invasive species, invasive species are generally larger, have higher specific leaf area , allocate relatively more biomass to leaves and stems at the expense of roots, and use resources more efficiently .

However, there are exceptions to every rule. Identifying traits associated with invasive species is hindered by differences in how invasiveness is defined, bias in species selection for experiments, and challenges comparing species at different stages of invasion . However, several useful frameworks have been developed to evaluate traits within relevant contexts. First, many researchers recommend controlling for a species’ commonness when selecting species for experiments as comparisons among common invasives and rare non-invasive species may lead to spurious conclusions . For example, invasive species appear to be more competitive than co-occurring natives ; however, many of these studies focus on particularly aggressive and common invaders. In a comparison of annual plants in Germany, Zhang and van Kluenen found that invasive species were stronger competitors only when comparing common invaders with rare natives. In essence, comparing species that are similarly successful should allow researchers to identify traits that promote invasion in particular, rather than commonness more generally. In another effort to standardize how invasiveness is defined, Catford et al. proposed comparing traits of invasive species within invasiveness categories based on four demographic dimensions: local abundance, geographic range, environmental range, and spread rate. One trait may promote invasiveness along one dimension but limit invasion along another . Time since introduction and propagule pressure would ideally be incorporated into invasiveness categories , but these data are not available for many species. Perhaps the most comprehensive effort to link traits to different stages of invasion is that of van Kluenen et al. who proposed a nested, multi-scale approach . Identifying a universal set of traits that explains invasiveness is challenging because traits are dependent on environmental context, including specific abiotic and biotic factors arising from, for example, climate and community composition .

By accounting for spatial scale, the framework proposed by van Kluenen et al. avoids inappropriate comparisons of traits across different stages of invasion and resolves inconsistencies associated with context dependency. For example, studies have found that invasive species can have smaller, similar, or larger seeds compared to native or non-invasive species . However, this inconsistency likely reflects different ecological filters or processes across stages: smaller seeds are likely to be dispersed to new sites, but larger seeds have more resources for establishment and growth . Conversely, some traits may enhance invasiveness at multiple stages of invasion. For example, fast growth rates can assist with colonization of new or disturbed habitats , lead to priority effects , and ultimately affect competition outcomes in established communities . Finally, a trait-based community assembly framework may also elucidate mechanisms of invasion . Community assembly theory allows for both stochastic and niche-based processes at various scales. Species composition within a community is determined by a series of ecological filters that sort species based on their traits . As an example, seed predation is a strong biotic filter on recruitment in some systems and this may favor species with smaller seeds that are more likely to evade predation from rodents . Investigating how trait-performance relationships change when a filter is manipulated can indicate if non-native invaders are succeeding by acting like the natives or by doing something different . Trait analyses can also determine if invasive species occupy empty niches. Work in desert annual communities in the southwest U.S. show that invasive annuals have unique trait combinations that allow them to grow fast and use water efficiently . Below, we expand on how traits and trait plasticity interact with abiotic and biotic filters to regulate invasion.Many invasive species thrive in resource-rich environments . Environments with ample light, water, or nutrient availability could favor fast-growing species that quickly take up available resources. Species associated with a resource acquisitive strategy have trait values aligned with the ‘fast-return’ end of leaf, plant, and root economic spectra . This includes cheaply constructed, short-lived tissues designed for high rates of carbon and nutrient assimilation and biomass allocation patterns that favor light interception and growth . These species may alter the system in a way that prevents slower-growing species from establishing and dominating. For example, hydroponic flood table the proliferation of invasive grasses in many systems suppresses woody seedling establishment via competition for limiting resources or increased fire firequency leading to a type conversion or invasion by other species . Many species can also invade low resource environments and they succeed by employing a wide range of strategies . Community assembly theory predicts that strong abiotic filters in stressful environments will result in co-occurring species with similar traits and there is some evidence for this in invaded systems. For example, species invading low resource systems are similarly or more efficient at using limiting resources relative to native species adapted to those systems .

There is also evidence that invasive species can succeed in low resource environments by possessing resource acquisitive traits. While native and invasive non-native annuals in semi-arid Mediterranean-climate ecosystems are similar with respect to most traits, invasive annuals were taller and had larger seeds and thinner roots—which likely enhances establishment and resource acquisition . Phenological differences, such as early germination, may allow invasive species to avoid competition from co-occurring species in low resource environments . Early phenology coupled with high resource-use efficiency or rapid growth may be particularly effective in low resource environments, such as deserts and coastal sage scrub in the southwestern U.S. . In sum, the fast growth rates and competitive strategies hypothesized by Baker appear to promote invasion in a range of habitats, but the specific physiological traits underlying these strategies differ across environments. Resource acquisition traits may be particularly useful in high resource environments, while efficient resource use or competitive strategies like early phenology may lead to invasion success in low resource environments. Finally, a central tenet of Baker’s ideology is that some invaders display broad environmental tolerance and are able to move past environmental filters by possessing traits that promote high fitness under low and high resource conditions. Some invasive species exhibit broad environmental tolerance by not conforming to growth-stress tolerance tradeoffs. For example, Norway maple is a common invader in North American forests and has high survival under low light conditions and high growth rates in full sun . Tree of heaven is one of the most invasive woody species in Europe and North America and its broad geographic distribution is driven by a combination of traits aligned with high resource acquisition as well as the ability to alter morphological traits and biomass allocation patterns across environments . During the invasion process plants may escape specialist enemies that limit their population growth in the native range . Such escape is typically transient, however, as invaders accumulate new enemies over time . The initial escape from enemies could allow for rapid establishment but, over longer timescales, three traits of invaders may make them particularly adept at overcoming the biotic filter created by enemies and promoting invasion. First, ruderal invaders can escape their enemies by virtue of their high dispersal, short lifespan, and low allocation to defense, fireeing up resources for rapid growth or competitive ability . Second and relatedly, many invaders appear to have high growth rates, which tend to reduce the cost of damage . This high growth rate means that invaders can withstand high amounts of enemy damage with limited effects on fitness . Consistent with this idea, in a multi-species study, invasive vines received just as much herbivory as natives or naturalized species, but were also more tolerant of damage , although other multispecies studies and metaanalyses find that invasives are similarly or even less tolerant to herbivory than natives . Third, native generalist enemies may have reduced preferences for non-native species with which they have no evolutionary history , although this appears not to be a general phenomenon across invasive species . Thus, both innate traits of the invader that Baker hypothesized would facilitate invasion and the match between invader traits and the invaded community may reduce the capacity for enemies to limit invader population growth. Like enemies, mutualists may also be left behind during the invasion process. As a result, successful invaders might be less dependent on mutualists , more generalist and able to interact with a wide variety of partners as predicted by Baker , or rely on co-invasion of mutualist partners . For example, selfng was one of Baker’s ‘ideal weed’ characteristics because it would allow reproduction in the absence of suitable pollinators and at low population densities. Selfers do appear to be over represented in invasive taxa although it is not clear whether this is because of the advantages of selfng when suitable pollinators aren’t available or because of Allee effects. For other species that fail to meet Baker’s criteria of generalized dispersal or pollination mechanisms , like that of highly specialized fgs which require a specific species of wasp pollinator or pines limited by appropriate mycorrhizae, invasion can still occur but only once the mutualist also invades.

Where other buyers exist, producers may try to increase property rights and bargaining power by retaining ownership of any surplus yield. For example, the contract could explicitly reserve any production surplus over the maximum to the producer or preserve the right of the end-user to request surplus biomass priced under the contract’s default compensation provision. On the other hand, contracts also must consider allocation of catastrophic risk. Over time, it is likely that weather, pests, drought, flooding, wind, or hail will impact biomass production on a given farm. No such product exists for biomass as of this writing. End-users require a consistent supply to accommodate conversion facilities, but a biomass farmer that fails to harvest a crop 243 has no revenue to perform the contract via spot market purchases—especially when there is no spot market for biomass. Accordingly, contracts should specify conditions for performance excuse and contingency provisions. Moreover, in the absence of a government safety net along the lines of crop insurance, biomass contracts should consider minimum revenue provisions to provide the farmer with some compensation. One way to soften this effect on the end-user is through the use of an amortized payment schedule. Producers would receive a guaranteed cash flow during all years of production to cover costs, but later payments could be diminished to allow the end-user to recover the costs throughout the life of the contract. Contracts could also require crop insurance, once available, botanicare trays and use insurance proceeds to offset initial contingency provisions.Once the crop is established, producers face a number of issues during the growing phase.

Some production contracts may require very specific production practices in order to decrease end-user supply risk and require monitoring of crop quality. These requirements decrease producer autonomy, and diminish potential gains from producers’ individual management skills and experience. Heavy requirements may also restrict the producers’ flexibility to adjust management practices to various production environment scenarios. On the other hand, considerable production risk arises from inexperience and lack of knowledge with producing energy crops. Inexperience or ignorance may cause a producer to adopt a production practice harmful to the crop or environment. In addition, the producer may be unsure how to address new production hazards, such as a new pest, drought conditions, or invasiveness. Thus, inexperience and lack of knowledge creates risks and costs for producers. End-users may desire to increase producer control through the biomass production agreements. As a general rule, however, contracts should allow producers as much freedom as possible to choose production practices. A principle of the Sociological Compatibility perspective is that producers value autonomy and demand compensation in some form for the loss of autonomy to satisfy participation constraints. Moreover, adjusting cultural practices is a traditional risk management tool for producers. For example, producers may choose to apply fertilizer in the fall to avoid higher prices in the spring, decide to plant later to avoid risk of a late frost and insect pests, and producers may choose to plant herbicide resistant crops and apply herbicides rather than mechanically cultivate crops to reduce weed competition. Because incentive contracts enhance producer risk, and rigid production practices foreclose other risk management strategies, other methods of dealing with end-user production risk are preferable. In other words, production practices have very poor separability, and thus respond poorly to incentives.

A better strategy may be for biomass production agreements to employ the use of generalized legal standards rather than specific practices to control production, which would shift contracting costs from the front to back end, while providing greater producer autonomy. A singular focus on incentives to maximize yield, however, is fraught with potential downside risks to long-term sustainability and suitability with end-user needs. For example, there is a tradeoff between corn stover removal, soil erosion, and fertilizer inputs. Removing high percentages of crop residues increases the risk of soil erosion from water and wind. Excess stover removal to increase per acre yield in one year will require additional fertilizer for the following crop year. Excess fertilizer can then impact the composition of the resulting biomass, especially its mineral content, which can then impact the ethanol conversion process. Additional fertilizer application also shifts the carbon footprint of the biomass feedstock or precipitates other environmental externalizes . Research also has suggested that the loss of soil organic carbon serves as an additional constraint for corn stover harvest. Similarly, harvest timing and cutting depth of both corn stover and perennial biomass crops must balance yield, moisture content, nutrient storage in the rootstock, soil compaction, and wildlife habitat over the winter. At the establishment stage, producer discretion in initial crop variety selection could impact potential invasiveness or migration of genetically engineered plants.  Accordingly, incentives in biomass supply contracts should provide producers sufficient flexibility to manage production and harvest decisions within the context of their other farming operations and long-term environmental values. As discussed in more detail in Section IV, infra, sustainability standards address many of the environmental tradeoffs identified above and embed balancing criteria to allow for producer autonomy within the context of environmental, social, and economic sustainability. Incentive contracts could look to or even incorporate third-party sustainability certification programs for guidance in allocating risks and responsibilities among producer and end-users with respect to balancing yield with environmental impacts.

In addition to, or complementary with, third-party sustainability certification, monitoring through the use of fieldmen may provide the most favorable strategy to address moral hazard during establishment and maintenance. Although developing the fieldmen model may take time, the benefits discussed in the framework likely outweigh the costs. Contracts can incorporate this model by elaborating on the “cooperation provision” outlined in the information sharing section. In addition to requiring notification of any material change in circumstances that may affect performance of either party’s obligations, the contract could create a right of the end-user to inspect the producer’s premises. In order to be of value to producers, end-users should employ the services of agronomists or individuals with knowledge and experience in biomass crop production, a requirement likely worth adding into the contract. Qualified fieldmen also can provide an excellent avenue for information sharing and education—an important risk management tool. In addition to inspections, the contract should authorize producers to request fieldmen services. Moreover, fieldmen could be enabled to authorize contract modifications or excuse performance. This strategy enhances producers’ social interaction factors, and could be coupled with assistance for sustainability standard certification.End-users deploy biomass production agreements to secure a stable supply of biomass, as well as other important characteristics, such as moisture level, foreign matter, mineral profile, BTU content, size and shape, and its environmental footprint. Risk arises when the producer is required or incentivized through penalties or bonuses for these crop attributes. While the producer may have control over some attributes, others evade manipulation. Strict consequences, such as rejection or price docking, create large risks for producers. Moreover, when minimum requirements are defined loosely, end-users may be able to engage in opportunistic behavior. To minimize holdup, biomass contracts should incorporate reasonable margins of error to account for normal environmental characteristics, as well as procedures for third-party verification and re-measurement.Storage and transportation of the low-density, high-volume biomass from the producer to the end-user presents unique challenges and should be considered carefully in the biomass supply contract. Assigning responsibility for storing and transporting implicates both risk- and cost-minimization strategies of contract design. For example, a set delivery date in the contract provides certainty, but indirectly assigns the storage burden—perhaps to both parties—and requires careful planning. On the other hand, an “on end-user demand” clearly shifts responsibility for storage to the producer and may dictate harvest timing despite other agronomic or environmental considerations. In contrast, an on-harvest delivery term places storage responsibility—and attendant risk of loss—on the enduser. Transportation responsibilities tie directly into product specifications and storage. If the contract requires certain harvesting methods or preprocessing requirements, flood table such as pelletizing or densification, the farmer may incur significant upfront equipment costs to produce the required result. However, some producers seek flexibility to minimize processing and transportation costs, such as forage chopping, directly into road transportable wagons, or pelletizing biomass in the field to decrease volume. In sum, up-front consideration should be given in the contract to linking product specifications with optimal storage methods to minimize post-harvest loss and maximize transportation efficiencies. The very high level of asset specificity, along with specialized equipment, places significant post-harvest risk in the farmer who has little bargaining power in a single-buyer market.

Accordingly, a more complete contract to minimize hold-up risk may be necessary to induce contract acceptance by the farming community.From a producer perspective, several factors influence the choice of land for biomass production. Perhaps most important is opportunity cost. In the Midwest, where much of the land is highly productive and can support currently higher value crops , energy crops, such as Miscanthus and switch grass, are unlikely to compete for scarce land resources. Biomass may be relegated to more marginal lands with lower opportunity cost, such as pasture or hay ground. Perennial biomass crops do provide, however, a number of environmental benefits, such as erosion control, improved soil and water quality, increased wildlife habitat, and increased soil organic carbon. Producers, therefore, may want to take advantage of these benefits and grow energy crops on at least marginal land to provide these long-term and environmental benefits. In addition, studies have shown that soil types can affect the composition of biomass plants, such as the percentage of lignin, cellulose, ash, and mineral content. In this way, land choice can significantly influence the quality and value of the resulting biomass crops. End-users have two strong preferences concerning the choice of land. First, in order to secure a stable biomass supply, endusers would prefer to tie biomass production to land title, rather than tying production requirements to individual producers. This strategy permits end-users to be less concerned with producer default, as land resources remain dedicated for biomass production. Other than outright purchase of land by the enduser, more creative avenues exist, such as equitable servitudes, covenants, or easements, to produce biomass that would attach to land title and provide more supply security than long-term lease agreements. Second, end-users prefer that biomass production be located near the end-user’s facility to decrease transportation costs. Where the end-user assumes the responsibility of transporting the biomass, local production is especially important. Longer transportation routes also increase greenhouse gas emissions, thereby decreasing the energy balance of the crop. Local production creates cost and risk for producers in two main ways, however. First, producers lose the traditional agriculture risk management strategy of geographical diversification; they cannot spread out production over larger areas to decrease weather and pest risk. Second, requiring local production limits the producer’s ability to produce energy crops on marginal ground or land exiting the Conservation Reserve Program. These production dynamics create a number of concerns for producers. First, as discussed in the Sociological-Compatibility Perspective, a producer may be unwilling to relinquish that level of control over his land; producers’ land is usually their most critical asset. Second, the greater the degree the land title is locked into biomass production, the greater the level of asset specificity, increasing the risk of holdup or renegotiation. Moreover, most producers grow crops on a combination of owned and leased land, with farmers depending on rental land resources to achieve economies of scale. Tying biomass production to land title, therefore, tightens the producers’ participation and incentive compatibility constraints and necessitates higher compensation.On the other hand, the multi-year production cycle for perennial biomass crops injects unique risk concerns into the farmland rental market. Producers may have difficulty securing leases for the duration of the production contract or even the life cycle of crops, such as switch grass and Miscanthus. Moreover, landowners may be concerned with the short- and long-term effects of biomass production on the land itself, or how to remediate the land back to its prior use if the end-user defaults on the biomass supply contract—a particular concern due to asset specificity. To provide safeguards and regulate producer practices, traditional leases have often relied on legal standards and duties . 

Offered the choice of these two contracts, the high-cost producer will choose Contract 1, as he will profit $1, and cannot profit from Contract 2, as his costs outweigh the compensation for 100 tons. The lowcost producer will always choose Contract 2. Although he could profit $2,301 under Contract 1, Contract 2 is designed to allow the low-cost producer to profit $2,302 and produce the maximum of 100 tons. This menu of contracts thus satisfies both producers’ participation and compatibility constraints, and incentivizes both parties to reveal their types by their contract choice. Note that offering this menu of contracts results in higher production at lower costs than rationing . Note also that the end-user still must pay the low-cost producers’ information rents in order to incentivize acceptance of the contract designed for the low-cost producer. Screening thus decreases, but does not eliminate, the rents low-cost producers can extract from private information. The amount of biomass that the high-cost producers can contract is also limited in order to make the high cost contract less desirable for the low-cost producer. Additionally, screening may limit producer participation. Screening presents another significant challenge for Principals. In order to design a menu of contracts to satisfy both the participation constraints and incentive compatibility constraints of producers, the Principal must have detailed knowledge of the characteristics and distribution of each type of producer. To the extent that an end-user’s understanding of producers is lacking, especially in a fledgling industry such as energy biomass, trimming cannabis the value and feasibility of screening may be limited severely. A third method to address adverse selection is through the use of auctions, specifically procurement auctions. In a procurement auction the buyer invites bids from suppliers for a specific contract. 

In auctioning, the lower-cost producers can still extract information rents from the end-user, as they must only offer a price just below the next lowest bidder, a strategy called bid shading. Therefore, they always offer a bid higher than their minimum bid, extracting the difference as information rent. The lower-cost the producer, the higher the information rent they can extract, while the highest-cost producer again cannot extract any information rent. While auctions again only minimize and do not eliminate information rents, auctions provide several advantages over other methods, such as screening or rationing. In theory, auctions can reduce the information rents without limiting production . For example, while rationing uses fixed prices and screening limits to decrease the attractiveness to low-cost producers, auctioning uses competitive bidding to achieve the same purpose. Finally, auctions dispense with the need of the end-user to know the cost distribution of different types of producers, and reveal changes in this cost distribution over time. On the other hand, auctions present some unique challenges. They require a critical mass of bidders to ensure competitive bidding, and create more uncertainty for the buyer , as they offer fewer predictions of producer responses. In addition, auctions can be costly and complicated to design and administer. A final strategy to address adverse selection is signaling, where the informed party acts first to reveal their private information to gain an advantage. This strategy has direct implications for both Principals and Agents. In a simple form of signaling, the Principal gathers information on observable characteristics of producers that are correlated with opportunity cost or other hidden information variables. Based on this information, the Principal can create minimum eligibility requirements for contracting. However, to prevent low-cost producers from masquerading as high-cost producers, the observable characteristics must be costly to fake. Also, information collection can be costly, and “the ability of this information to reduce information rents without distorting [production supply] will only be as good as the strength of the correlation between the characteristics and [producer types.]” 

Some producers, may also find it in their best interest to take the initiative to use signals to reveal their private information . End-users can increase supply while limiting the potential for information rents by contracting with high-cost producers that effectively signal their type. By requiring signals that are impossible or costly to mask , the end-user can obtain the added production from high-cost producers without the risk of paying increased information rents from low-cost producers masquerading as high-cost producers.While adverse selection problems arise during contract negotiation, moral hazard emerges after the contract is signed. Moral hazard exists where the Agent makes a decision that affects the utility of both the Agent and the Principal, the Principal can only observe the outcome of the decision, which is an imperfect indication of the action, and the action that the Agent would take to maximize his utility does not simultaneously maximize the utility of the Principal . Information asymmetry in this case again gives rise to opportunistic behavior on behalf of the informed party, as they may shirk their effort. Literature from sociology and economic contract theory has developed several tools to address moral hazard problems. To model this problem, we offer a second simple example in which an end-user has contracted with a producer to produce and deliver biomass. Assume that a producer’s yield depends on two variables: his effort , which is costly to the farmer; and the weather. The end-user and producer have signed an acreage-based supply contract, where the farmer is to deliver the entire crop from 50 acres of land to the end-user for a fixed price per acre. This scenario gives rise to moral hazard, as the farmer has an incentive to slough off, a decision that conflicts with the interest of the end-user seeking to maximize yield from the land under production. Perhaps the most powerful tool available to address moral hazard is incentive contracting, developed in complete contracts literature. However, incentive contracting also creates the trade-off between risk and cost discussed earlier in the Risk Minimizing Perspective. 

The economic contract literature assumes that only the outcome of the Agent’s decision is observable, and thus the Principal can only influence the choice the Agent makes by conditioning the Agent’s utility on the outcome. However, because the outcome is imperfectly correlated to the Agent’s actions due to the variability of weather, basing the Agent’s utility on outcome imposes risk for the Agent. Once again using mechanism design, the Principal must maximize his utility subject to the producer participation constraints and incentive compatibility constraints. The incentive compatibility constraints imply that the contract must provide enough incentive that the producer prefers to put forth effort. For example, the producer must profit more from applying fertilizer than from failing to apply it. In our example above, where the end-user can only observe yield, the end-user can only base incentives on yield. Because application of fertilizer positively correlates with yield , the end-user could modify the contract to award a bonus for achieving a certain threshold of yield. If the end-user can renegotiate the current contract, he might desire a price-per-ton contract over an acreage contract, to tie the Agent’s utility to outcome . The proposition is quite a simple one: the end user will give the Agent a higher payment when the end-user can infer from the outcome that the Agent made a favorable decision, and vice versa. While both these solutions may satisfy incentive compatibility constraints by incentivizing the farmer to put forth effort, they also increase risk, which serves to tighten a producer’s participation constraints. In order to incentivize the producer to accept the incentive contract, the end-user must also satisfy the producer’s participation constraints. Participation constraints may include a host of factors, economic and non-economic, and the producer’s aversion to risk. Therefore, cannabis drying rack as risk is passed to the producer to satisfy incentive compatibility constraints, end-users must provide larger payments to satisfy the producer’s participation constraints. The extra compensation that the Principal must pay is an information rent that arises from the asymmetric information between the parties. Within this general theory, several important principles emerge. First, the smaller the expected difference between outcome of a favorable Agent action and an unfavorable one, the larger the incentive must be to motivate the Agent to act. The reason is because it becomes more difficult to distinguish between the Agent’s action and inaction. Also, the optimal strength of incentives is dependent on several factors. Second, the greater the value of any additional producer effort and the greater effect the incentive will have on the producer’s behavior, the stronger the incentive should be. Finally, the tradeoff between risk and incentive implies that weaker incentives should be given to more risk-averse producers. A more difficult problem arises, however, when a Principal has multiple objectives to maximize, and a producer’s single action affects both objectives. When a producer’s action supports one goal and opposes the other, incentive conflicts arise. The optimal balance will occur where the marginal benefit gained from incentivizing the producer to act to support one objective is equal to the marginal cost of the detriment to the conflicting objective. The value of incentive contracting is limited by more than the risk-cost tradeoff. Incentive contracts assume that outcome, and only outcome, is observable, and the Principal cannot gather additional information. Incentive contracts also assume that the Principal has no way to force the Agent to act.

While in some scenarios these two assumptions hold true, the agricultural context provides unique opportunities to employ additional tools to manage incentives.Incentive contracts rely on “quality measurement,” an observation limited by numerous factors, including the above mentioned inability to distinguish between quality arising from producer effort and quality arising from fortuitous circumstances . While yield is fairly easy to measure, other crop/production characteristics are more difficult to assess at delivery, such as moisture and ash content; carbon footprint; and other sustainability attributes . Large crop volumes, high costs of measurement technology, limited time, and logistical complexities further limit measurement ability. Also, when measurements are controlled by a single party, the risk of opportunistic behavior arises from measurement errors or fraud. Parties can address this risk, although at a cost, by employing third-party verification or allowing the other party to re-test. These terms refer to measurement characteristics of a transaction that reflect both the asymmetry of information and the costs of monitoring or verifying individual performance. Separability refers to the “ability to evaluate an Agent’s effort just by observing output,” or “how much of the quality/quantity of the product is measurably attributable to the producer’s management efforts[.]” Programmability refers to “how closely output is tied to specific input decisions and observable management practices.” Production processes that are highly separable are appropriately addressed by incentive contracts, as the “allocation of value and risk will be efficient.” Utilizing incentive contracts for production processes that are not separable creates weak incentives, increases producer risk, and also creates risk of opportunistic behavior by the producer. If production is not separable but highly programmable, contracts can better address moral hazard by controlling the production process, depending on the cost of monitoring. Increasing control through more complete contracting has several drawbacks, however. First, end-users must incur the cost of writing and enforcing additional contract provisions, which may require additional monitoring and enforcement effort. Decreased producer autonomy also requires compensation to overcome participation constraints and disallows potential gains from the producer’s specialized knowledge and skills. Two common examples of this type of control in the agricultural context are production contracts for poultry and hogs—both of which have engendered substantial farmer criticism due to perceptions of feeling trapped or intimidated by the contracts offered by the end-users of their products. An alternative method for the Principal to manage moral hazard is via monitoring. One policing model that end-users could employ is the use of field men, who periodically visit producers. Creating a network of field men yields a number of benefits. First, monitoring in this way increases the number of observable variables, by not only observing directly the production capabilities and practices of individual farmers, but also observing the production environment beyond the producer’s control, such as weather and pest problems. If the field man perceives opportunistic or suboptimal behavior on behalf of the producer, the field man can address the problem before damage occurs to the crop. Although field men may be perceived as “supervisors, spies, or adversaries,” they can provide multiple benefits for producers, and farmers rarely have negative perceptions of these observers.

UK farmers indicated to me that such practices might give them an edge in meeting food safety concerns, but would be simply impossible due to how they would change the farm’s outward face. Part and parcel of this issue, UK “right to roam” laws grant the public the right to walk freely across privately owned parcels of land, along with their domestic animals. This comparatively open and unsecured way of managing farms would make many of the secure fencing and private property-based exclusion measures common in CA incongruous with the English rural landscape, and, in some cases, potentially illegal or flat out impossible to implement. When I surveyed on-farm practices for food safety and conservation, UK farmers were especially unlikely to remove vegetation from around ditches, ponds, and field margins. When I asked them why, farmers indicated to me that the idea of doing so seemed to conflict not only with the right to roam, but also with a popularly held idea of the proper role of a farm as a wild environment. During our interviews UK farmers often noted that local community-level rules governing the cosmetic appearance of agricultural fields and associated facilities would prohibit the removal of vegetation around field margins, ponds and watercourses which otherwise serve a scenic purpose. Even without that constraint, treating the farm as something other than a wild place did not seem right to the majority of farmers I spoke with. Those who did not espouse this view operated the largest farms in my sample, and were those most likely to protect their crops under the cover of large scale glasshouses. California’s longstanding legacy as a highly capitalized agricultural economy dominated since its founding by large farms, commodity crops, drying weed and production-oriented agricultural methods has created a long-standing capitalist framing and sense of separation between agricultural and residential or recreational lands .

Farming in California is clustered into areas of historical agricultural intensification, far from the population centers of urban and suburban living. On these dedicated agricultural expanses, land management decisions are somewhat insulated from conflicting suburban views of what agriculture should be or should look like. The sheer amount of land available for agricultural use in the United States generally and California specifically has allowed agriculture to make its own rules, less concerned with sharing space with nearby towns. California farmers I interviewed indicated that they were consumed entirely by the challenge of maintaining the land they have while producing the crop their buyers wanted to see, in the ways required by law, standards, and buyer requests. They primarily focused on economics and capacity when deciding how to do so, and what it looked like to anyone outside of the farming lifestyle was essentially immaterial. Illustrating this difference, the California farmers I interviewed agreed with their UK counterparts that agricultural lands can serve a valuable purpose as wildlife habitat if practices such as clearing buffer strips and erecting wildlife exclusion fences are not undertaken, but this fact was most often mentioned by them as a serious liability rather than a competing desired outcome. At best, it was noted as a fraught conflict between different sets of values; on the one hand, there were what they saw as the ideals of environmental health, or romanticized notions of productive wilderness and movements ‘back to the land’, and on the other side came the discordant reality of what is feasible on tight economic margins and large commercial contracts, and what is simply too risky to—quite literally—bet the farm on. Their explanations highlighted values echoed by my UK sample: commitment to safe food, respect for nature, and the desire to protect both the long-term financial and ecological viability of their farms. However, California farmers in my sample did not mention being motivated at all by values associated with the scenic appearance of their fields, or the accessibility of their land for recreational value.

These values did not appear to be strong motivators for their practices in comparison with the clearly articulated expectations of food safety audits and buyer requirements.Lastly, as my field work progressed, I found growing evidence that farm ownership patterns may be having a specific impact on certain kinds of food safety efforts. Specifically, farmers with a deep personal connection to the land they farmed described their on-farm food safety practices in language that made explicit reference to environmental health as a component of safe food. Since the late 19 century with the advent of modern farming technologies and increasing th concentration of populations in urban centers, many the industrialized nations of the Global North have experienced a sharp decline in the percentage of their populations working in agriculture . Falling numbers for population working in agriculture come on the heels of rising farm productivity and the development and proliferation of non-agricultural employment opportunities, all of which combine to endanger family farm ownership and the transgenerational transfer of farming knowledge. However, UK regulators and trade associations stressed for me that the majority of the farmland in the UK is nevertheless still family-owned and operated, often by families that have run their farms for generations. “It’s a long game,” I was told by one trade association representative who worked closely with farms. “This land has been theirs for a long time.” My archival research echoed this finding, and my interviews bore this out as well. Most of my UK farms still under direct family ownership. In 7 several cases, I interviewed the farm’s owner, who was also the on-site harvest manager, and who shared a surname with the commercial name of the farm. Several more of my UK interviewees represented associations of several small family farms that had banded together to achieve economies of scale in a competitive agricultural market, but in a way that preserved individual family management of original family-held lands. Once this history was spelled out, I could see that the names of these companies often reflected their conglomerate nature through acronyms or group nouns composed of the sum of their parts. Importantly though, each family remained in control of the land it had brought to the association. Management decisions were still made at the local level, by the manager of each individual farm.

Several times my questions about farm management could only be answered by my initial interviewee for their section of the farm’s land, and I had to be routed to another family within the association to hear about management on their portion of the farmland . My work in CA suggested a subtle difference here, which was outside the scope of my research and would need to be verified and explored further. Family farm ownership is certainly not unknown in CA, nor is it especially uncommon. Several of my CA interviewees represented family-owned farms, even if the farm had never carried the surname of the individuals running it. Even one of the CA farms I spoke at length with, that was among the largest and the most factory-run and thus potentially the farthest from a pastoral family farming ideal, had started at one point as family farm and grown through land acquisitions. What I found important here was that the land had been acquired, not simply joined together in name. What had been a large number of independent holdings, some of which may have originally been family operated, was now a large conglomerate run by managers who do not and have never had a personal family association with the land they now manage. One of the farm managers I spoke with who worked for a CA grower that splits its production between California and Arizona depending on time of year, vertical growing systems told me that he moves to Arizona when the season there begins. Neither place is home, he reported; his family is in Georgia. This is a job.8 Scholars examining the sociology of rural agriculture have noted instances of this difference in other places and at other times. Comparing environmental regulation in the UK and US in the mid 1980s, David Vogel notes that greater population density and less available arable land in the UK has been a factor in making conservation and land use issues take center stage more easily than in the US . In the US, Julie Guthman has explored the history of California farming and its lack of a true family-farm agrarian past at any point. Instead, farming in CA has been pushed toward larger-scale and more production-oriented models that focus on large farms and high valuable crops, in part because of the high property values of CA land . From the descriptions offered by my interviewees, it appeared that persistent differences in how farmland is held and operated in CA and in the UK could be partly responsible for influencing farmers’ decisions about the importance of maintaining environmental sustainability practices alongside food safety requirements. If some degree of continued family ownership and personal connection to both the past and future of the land increases family farmers’ ability to think about food safety requirements with a long-term sustainability framing, this difference in land ownership patterns could be creating an environment where US farms’ environmental future is more likely to be discounted in favor of present food safety and economic concerns. However, UK farmers have already experienced and responded in their own ways to market pressures that have incentivized larger landholdings and more intensive production, finding ways to adapt that still preserve family ownership. As the UK grapples with the coming challenge of competing on a global marketplace as a single nation apart from EU common market, it is unlikely that these pressures will lessen. Thus, UK agriculture may be in a transitional period, and headed for a new period of changes in historical patterns of family farm ownership.In the years since my research first began, the state and non-state food safety controls examined in my study have undergone several important changes with the goal of reducing the duplicative and redundant landscape of safety controls active in the fresh produce market. One of the first such efforts was the Global Food Safety Initiative bench marking effort. Since its launch in May of 2000, GFSI bench marking has attempted to certify for equivalence many disparate food safety standards operating in multiple food supply chains around the world. GFSI gained recognition in 2007 after seven major global retailers announced they would accept any GFSI-bench marked safety standard. Nevertheless, wider acceptance difficulties remained, and 9 events such as the 2006 outbreak of E. coli in California spinach caused a further proliferation of standards rather than an easy convergence around fewer standards or robust bench marking. After a lengthy and remarkably inclusive multi-stakeholder process with the goal of identifying a single safety standard that could serve as a commonly accepted guaranteed of good practices in any national or international market, the United Fresh Harmonized GAP Standardwas created in 2016. In partnership with GlobalG.A.P., the Harmonized Produce Safety Standard was born , and later became the USDA Harmonized GAP standard. However, the multi-stakeholder harmonized safety standard created in the aforementioned process was not unified for long; in the course of obtaining GFSI bench marking, GlobalG.A.P. was forced to update its harmonized standard to a version different from that adopted by the rest of its partners in the original harmonization process, creating a proprietary GlobalG.A.P. 10 harmonized standard alongside the USDA Harmonized GAP standard. The differences between those two standards were small, but in essence, there were still multiple standards even after the harmonization efforts and the attempts to use bench marking to level playing fields between different standards. In the context of my research, the private standard for which I gathered the most evidence of positive outcomes in farmer experience and environmental sustainability, the Tesco NURTURE program, has also now been subsumed under the umbrella of the most recent Global G.A.P. HPSS. The Tesco NURTURE program provided much of the basis for my conclusions favoring the results from private standards that use a balance of regulatory styles and a wide view of food safety that includes environmental considerations. Both Global G.A.P. and NURTURE were among my category 4, representing standards that were the most balanced in both style and focus. As a module within the newest version of the Global G.A.P. standard, NURTURE’s transformation is an early example of one possible outcome of ongoing efforts to achieve harmonization between the many overlapping food safety standards current active in fresh produce markets.

Additionally, two of the standalone standards were excluded from the analysis: Marks & Spencer’s ‘Field to Fork’ was excluded entirely because an audit checklist could not be obtained for review, and GlobalG.A.P. was excluded from analyses of farmer opinions and practices because only four farmers in my survey results for either nation claimed to carry this certification. The results presented here represent a combination of personal interviews and archival research, conducted during field research between 2014 and 2017 in multiple locations across California, and the United Kingdom. I report here the results of two different survey efforts. The first survey, piloted and released in 2014 to members of the California Farm Bureau Federation, yielded data for forty-nine California lettuce growers as part of a larger survey effort covering 965 California growers of a range of crops . This survey was designed to update prior 3 scholarship examining food safety measures among California farms since 2007. For the purposes of my research, I conducted five additional in-depth interviews with California farmers, two with regulators, and three with academic researchers to contextualize the results of that broader survey and inform my analyses of the responses of lettuce farmers who took part. The second survey reported here includes data from twenty-one in-depth interviews I conducted with UK farmers of leafy greens, designed to mirror the structure and topics of the survey delivered to California farmers. Further information is provided by nine additional in-depth interviews with representatives of major UK grocery retailers, academic researchers, indoor grow methods farmers’ trade associations, and food safety regulatory personnel, conducted in the United Kingdom between Summer 2014 and Spring 2016.

In-depth interviews during both research efforts followed a semi-structured format tailored to each interviewee’s unique position of knowledge within the food system, focused on elucidating the mechanisms behind how decisions are made at both the regulator and food retail industry level, what food safety and environmental pressures farmers experience, and in what ways differential value is placed upon food safety goals and environmental outcomes. Both farmer surveys contained approximately 30 questions, ranging from farm area and crops grown, to perceptions of the food safety regulatory framework, to field level management practices in place for food safety or for the promotion of environmental protection. Full interview questionnaires for my California and UK survey efforts can be found in Appendices I and II, respectively. To understand the social impact of overlapping state and non-state food safety controls, respondents were asked to specify what, if any, food safety certifications they currently held, and how they felt about the certification process and the public regulatory landscape around food safety. Farmers were additionally asked to assess which actors in the lettuce supply chain held the most power in setting field-level farmer practices, and in shaping the overall food safety regulatory landscape. Field level production practices were analyzed quantitatively, by assigning each farmer scores for food safety and environmental conservation. Interviews conducted in person followed the general structure and questions of the survey questionnaires, while also incorporating additional questions and further exploration of survey topics led organically by interviewees’ interests and expertise. To supplement data from interviews and survey results, I also present insights from an analysis of regulatory styles found in state and non-state food safety controls. To compare methods of state regulation of food safety across the United States and United Kingdom, I evaluate the most relevant food safety laws in each nation for their regulatory style and topics of primary focus.

To illuminate the landscape of non-state food safety standards, I present a comparative analysis of the structure and written requirements of eleven produce safety standards operating across the UK and California. Each standard was evaluated through its certification audit checklists, by assessing each audit clause or certification criterion within the standard for its topic focus and its regulatory style , enabling a quantitative comparison between standards. To compare the regulatory landscape emerging from the overlap of these state and non-state controls, I compare the approaches of both private and public food safety controls by organizing them into four categories based on focus and style. Because the two farmer surveys summarized in this dissertation were conducted during separate field seasons and survey efforts, the total number of respondents for each survey is not equivalent. Twenty-one UK leafy greens farmers were surveyed, compared to 49 US farmers. These differences reflect differences in response rate, as well as limitations due to amount of time in each location and different recruitment methods. In addition, because participation in data collection was entirely voluntary on the part of farmers, not all survey respondents chose to answer all questions on the survey, with the end result that the number of responses analyzed from each respondent group varies slightly from question to question on both surveys. Survey questions themselves also differed in some respects between my US and UK surveys. The survey instrument used for UK farms used slightly different language from that used in California, an intentional step designed to adjust for local differences in terminology related to various practices, as well as different local concerns, local policy bodies, and local supply chain structures. As a result, some information is reported for only one study population, and any comparisons of non-parallel data types will be clearly noted. Additionally, all reasonable efforts were made to ask questions in locally appropriate language and terminology for each study population, resulting in slight variations in wording between the two surveys.

Rather than increasing differences between the surveys, these adjustments were intended to reduce variation resulting from differences in language, and to ensure that variation observed was a faithful representation of actual practice and actual perceptions of governance institutions.This study focused on evaluating public and private standards and their impacts on farmer practice and farmer decision-making as a result of produce standards and regulations. Because my focus was on farmer experience, and farmer decisions in the realm of environmental conservation—the ultimate outcome of multiple overlapping governance forces as seen by farmers rather than by regulators—I did not specifically investigate details of how the preregulatory risk assessment scheme Red Tractor Assured Produce and the industry-led harmonization effort by the British Retail Consortium may influence the form that public regulation takes in the UK, or the articulation of public and private regulatory processes. Rather, I have evaluated those two standards at face value as component standards within the regulatory landscape, because that is how farmers experience them. For similar reasons, I have compared the explicitly pro-environmental Linking Environment And Farming standard alongside other non-state food safety controls with fewer explicit references to environmental conservation because farmers indicated that they regard LEAF as a safety standard comparable to any other I examined. My analysis acknowledges and aims to engage these differences as a meaningful indication of how environmental conservation is valued by a range of food safety controls active simultaneously in the lettuce production market.As a starting point for my comparison, I examined the state regulatory frameworks in place for produce food safety in the United Kingdom and United States. At the time of this research, the UK was a member of the European Union, meaning that national food safety regulation in the UK is shaped by EU requirements, and vice versa, in a shared governance arrangement that incorporates a multi-level strategic bargaining process and two-way transfer of priorities . The top levels of EU food safety regulation take two different forms: regulations and directives. Regulations apply to member states directly, cannabis dryer without any need for member states to create local interpretations. Directives, conversely, are general guidelines which member states must adapt to local contexts and implementation systems. Food safety goals are articulated here as broad principles which are meant to guide member states’ actions as they construct action plans specific to their industries and local administrative authority structures. Action plans must fit within the broad principles set forth by European Food Safety Authority , but must put them into practice by providing enforceable local regulatory specifics. Beginning at the highest levels of state regulation applicable for leafy greens production in the United Kingdom at the time of this research, European food safety rules are presented in Reg EC No 178/2002. This regulation standardizes food safety goals and definitions for EU member states and forms the backbone of the European food safety system. The regulation does not specifically address food safety concerns in individual foodstuffs or their respective supply chains, but rather focuses on establishing basic terminology and expectations, along with the procedure to be followed in cases where problems are known or suspected.

The regulation’s stated goals of “a high level of protection of human life and health and the protection of consumers’ interests, including fair practices in food trade, taking account of, where appropriate, the protection of animal health and welfare, plant health and the environment” makes explicit mention of a range of parallel goals that must be considered as part of food safety, including environmental health. Use of the precautionary principle is explicitly defined as a guideline for maintaining the safety of the food supply, along with risk analysis. Food businesses such as producers, processors, and manufacturers and retailers of food items are stated as the ideal controllers of food safety because of their proximate knowledge of any risks and appropriate solutions. Traceability is also elaborated as an important prerequisite of ensuring safe food. Article 18 of the regulation reads “The traceability of food, feed, food-producing animals, and any other substance intended to be, or expected to be, incorporated into a food or feed shall be established at all stages of production, processing and distribution.” UK food safety regulation within this European framework is layered beneath EU controls and is predicated on the UK’s 1990 Food Safety Act. The law makes no mention of produce or specific pathogens, following instead the general style of EC regulation in setting goals, definitions and procedures to be followed in the event of a problem. Section 7 of the act names as an offense “rendering food injurious to health” . In cases 4 where food has been sold that is injurious to health, the state can prosecute the provider of that food item under the law. Several defenses are listed which can absolve a food business of criminal responsibility, most notably the defense of due diligence, defined as “a defence for the person charged to prove that he took all reasonable precautions and exercised all due diligence to avoid the commission of the offence by himself or by a person under his control” . A subsequent law, the Food Standards Act 1999, established the UK Food Standards Agency and outlined its role as the controller of food safety within the United Kingdom. Pursuant to these two acts, the FSA has released numerous fact sheets and guidance documents interpreting the 1990 Food Safety Act for owners of food businesses. In a 2009 guide for food businesses, FSA presents examples of situations and actions that the 1990 Food Safety Act would apply to, and explains that the concept of due diligence is designed to protect both consumers and businesses. In their words, the due diligence defense is “designed to balance the protection of the consumer against defective food with the right of traders not to be convicted of an offence they have taken all reasonable care to avoid committing” . The FSA fact sheet Monitoring microbial food safety of fresh produce released in 2010 contains basic information on the names and risk factors for certain food pathogens with guidance for produce farmers in avoiding or reducing the potential for pathogen transmission through food products. The document emphasizes that there are “no statutory criteria for indicator bacteria on unprocessed fresh produce” and thus no specific microbiological targets that are required by law for fresh produce. Key practices recommended for maintaining microbial safety in produce include the use of potable water for irrigation, regular testing of water sources, avoiding the application of raw uncomposted manure on crops that are typically eaten uncooked, and minimizing the degree of contact between irrigation water and the edible portion of crops.In comparison, in the United States, government food safety is managed through a similarly multi-level array of federal, state and local bodies, with requirements that become more specific and enforcement-oriented at local levels.

To adapt direct regulation to new policy arenas and make regulation less costly and time consuming to administer, regulatory variations have appeared that seek to ensure the same outcomes with more efficient use of resources. Modified direct regulation strategies such as Risk-based Regulation and Responsive Regulation retain the basic administrative structures of direct regulation under command-and-control frameworks, while modifying interactions with non-state actors in order to create a less burdensome, more effective and more cooperative regulatory process . In Risk-based Regulation, risk assessments direct inspections and enforcement toward those firms most likely to fail, while low-risk firms enjoy lighter regulation, motivating firms to build a record of compliance . Similarly, Responsive Regulation seeks to understand and resolve barriers to compliance, avoiding the use of enforcement resources to clear up cases of ignorance and misunderstanding, so that they may be used instead only for more serious cases of noncompliance .Process-oriented approaches such as Enforced self-regulation, Management-Based Regulation, Systems-based regulation, Meta-regulation and Principles-Based Regulation aim to control how firms act, rather than directly mandating end results. These styles seek to improve on traditional direct regulation by allowing those closest to the problem to design the solutions , requiring only that solutions be developed internally and put into place. One possible drawback of this approach is that the outcome itself is left uncertain even when regulations function optimally; the possibility remains that firms may be in total compliance with the procedural requirements of this type of regulation, without actually achieving the desired policy outcomes.

Since the 1990s, rolling greenhouse tables many governments have also undertaken efforts to broaden regulatory participation to include a wider array of views and interests . These efforts have been made with the goals of heightening public awareness of regulatory issues and improving the quality of regulation for normative , epistemic , and instrumental reasons. It is unclear however, whether the goals of broadened participation have been, or can be, achieved in practice . However, it can be hard to strike a balance between democratic goals and policy goals, and broadening participation is often expensive. Scholars have also have argued that the success or failure of participative policy projects can hinge on “institutional fit” between the policy process and the beliefs and norms embodied within participation . Nevertheless, co-management may offer the best chance of managing complex social and environmental problems within multi-level governance systems . Although these variations of direct regulation offer improved solutions and more efficient use of regulatory resources, new challenges emerge. Research suggests that risk-based approaches may still suffer from many of the problems of direct regulation because the top-down regulatory style is still not necessarily fully responsive to the needs of industry . Some scholars also question whether these modified approaches truly deliver on the initial promise of regulation by ensuring desired outcomes, or whether they actually result in diluted, less effective regulation .Regulation achieved by non-state entities can take a wide variety of forms, including Information-based Regulation, Private Regulation and Self-Regulation. These forms differ from command-and-control in that rule-making power and enforcement authority are held not by state regulators, but by non-state actors . Self-regulation describes a process where public regulators grant firms the power to define their own regulatory targets and the authority to police their own activities, either individually or through industry associations.

In the food system, these approaches borrow from recent developments in environmental governance that seek to address perceived failures and inefficiencies of state-led regulation by shifting regulatory power to markets and market actors . Enforcement authority in non-state regulation derives from supply chain relationships and from economic concerns, rather than from government. Information-based Regulation seeks to increase the public availability of information about firms’ performance to encourage compliance. In Private Regulation, private actors assume the roles traditionally played by public regulators, by defining targets and directing inspections and enforcement. Private standards typically function alongside and in addition to public regulation but may also act to supplant public regulation where public enforcement is lacking, public standards are insufficient, or where no public response yet exists. One of the most notable benefits of non-state approaches is that they can move more quickly than traditional public regulatory processes, producing timely technical decisions which might have taken longer to emerge from a more accountable, representative public regulatory process involving chambers of government and bureaucratic agencies. This nimbleness can be beneficial when responding to new and emerging threats such as the environmental hazards of new and as-yet-unregulated technologies, or newly recognized public health threats which do not yet have established regulatory benchmarks but for which human suffering might be averted by swift action before such regulation is produced. Although self-regulation and private regulation may seem like the fox guarding the hen house, competition among rival firms can encourage stronger self-regulation as firms watchdog each other independent of public regulatory enforcement, avoiding a race to the bottom. In some cases, private regulation that is viewed as successful or politically expedient may even become hardened into law, generating new public regulation where none previously existed . However, private regulation’s nimbleness and relative lack of bureaucracy can also be an Achilles heel. Whereas governments are accountable to their citizens if their regulatory standards are found to be faulty, no such accountability is necessarily built into privately controlled regulation. The market primarily exerts influence over such standards, and the market can become a vehicle with no driver at the wheel. Private strategies thus reflect the character of their creators; they are as lax or as rigorous, as representative or as mysterious, as complete or as cursory, as the firms and public regulatory efforts that pursue them . If industry associations successfully create ineffective mandatory standards or if firms choose to sign on to those voluntary standards which ask the least of them, the market may experience a downward convergence onto the least effective standards . Self-regulation and private regulation may also be pursued by firms that specifically wish to avoid or to weaken public regulation. Poorly designed or bad faith private regulatory efforts can provide equally poor outcomes.The United States and the United Kingdom have very different agricultural histories, as might be expected due to dissimilar geographies and historical settlement patterns. The history of UK agriculture precedes modern civilization, evolving from a background of early subsistence activities and feudal peasant agriculture. Enclosures of public lands in the early stages of the industrial revolution disenfranchised Britain’s rural agricultural populace, while the role of capitalist production-oriented agriculture expanded to feed growing urban work forces . The current UK agricultural system combines elements of the social and landscape heritage of Britain’s long history of rural family farming with the modern style of capitalist production, within the trade relationships and political linkages of the European Union . Landholdings still often follow historical patterns of family ownership and traditions of land management, even while growing commodity crops meant for international markets . As a consequence of agricultural intensification driven in part by the supply chain activities of powerful food retailers, UK farming has recently seen an increasing reliance on migrant labor beginning since the 1990s . In the US, agricultural histories differ sharply along regional lines, based on timing and character of early post-colonial settlement. California’s agricultural history shares little with that of the UK. California’s relatively recent and highly capitalist agricultural industry did not develop from a history of small-scale, independent family farms, nor from feudal landholdings. California’s native inhabitants did not farm the land, and at no point in subsequent settler history was California host to a small-scale agrarian populace .

Instead, from its establishment around 3 the time of the Gold Rush in the mid 1800s, California agriculture has always been intensive, large scale, market-oriented, ebb and flow rolling benches and dependent on hired labor primarily supplied by migrant and ethnic minority communities, often under extremely exploitative circumstances . Despite the divergent starting points of their agricultural histories, the UK and US both experienced an increase in the public visibility of environmental and public health problems in the late 1800s and early 1900s. A new era of progressive policies followed, aimed at reforming core industrial activities and solving collective action problems in the large-scale production of public goods such as clean water and clean air . In response to a wide array of factors including political regime changes, shifting public opinion, and the rising power of global agribusiness, the approach of the two states has shifted considerably over time. Early in the period of heightened environmental regulation that began among most developed nations in the 1960s and 1970s, the United States was recognized as a progressive leader. The earliest US risk regulation in the realms of environment and food during this time took a precautionary stance that prioritized the public interest and sought to place limits on the activities of industry through ambitious and comprehensive formal regulation on topics including water quality, air quality, product safety, vehicle emissions, and chemical safety. In contrast, although UK regulation had established regulatory bodies dedicated to environmental problems in the mid 1800s, UK environmental regulation during this period was, during this early period, less ambitious than environmental regulation in the US. UK regulatory efforts moved slowly and incrementally, developing multi-sectoral scientific consensus before the drafting of legislation, and relying on trust between industry and regulators rather than enforcement and sanctions.4 Beginning in the 1980s, a wave of neoliberal reforms and deregulation during the Reagan administration changed the tenor of US environmental and public health policy. US risk regulation became more conservative and less precautionary in its approach and more protective of industry, as environmental and public health regulation came to be seen as a tax on industrial economic growth, and US regulators eschewed precautionary policy in food safety partly out of concern that a precautionary stance might present a non-tariff barrier to trade . US environmental law originally referenced precautionary reasoning in decisions around early environmental reforms but Congress and the White House later declared it improper to create policy based on uncertain risks, favoring scientific risk assessment in place of precaution . On this basis, the US adopted ambitious scientific standards developed without formal industry input, requiring mandatory use of the most effective technologies. While some degree of collaboration and flexibility entered the system through the implementation efforts of local regulatory authorities, the basic architecture of the system was built to rein in the activities of industry through the use of stringent direct regulation. Around the same time, the character of UK regulatory efforts in the environmental and public health arena, following the approach taken by the European Commission , retained their focus on trust and consensus, and became increasingly motivated by the precautionary principle. The British style emphasized the evolution of smaller, incremental targets, developed with the cooperation of industry through collaborative site visits and inspections, in a legislative process out of view of the public eye. These targets typically included deep collaborative participation by industry groups and less focus on adherence to rigid standards, allowing a greater emphasis on informal and voluntary participation . By the late 1980s, progress made by the two states on a host of environmental and public health issues showed similar levels of improvement, despite the fact that the two states had approached these regulatory challenges through very different means. The key difference in transatlantic environmental and public health regulation that emerged by the turn of the century was in the attitude of industry toward environmental regulation. In the US, environmental regulation became a highly politically polarizing issue seen by industry as a hindrance to economic growth, while in the UK environmental regulation never became as contentious a political topic, and the relationship of business to government remained focused on compromise and conciliation.In both the US and UK prior to the 1980s, risk management in food and agriculture centered primarily on economic concerns such as commodity production and price supports. Food safety surveillance had existed in both nations since the late 1800s for products such as milk and meat, but food safety was not a leading regulatory focus . Growing awareness of the risk of pathogens in the food supply began to put food safety at the top of the regulatory agenda following the emergence of a new range of public health concerns which focused attention on food production practices and revealed the inadequacy of existing regulatory controls to deal with pathogen threats .

The main advantages of PV include: simplicity of the direct photoelectric conversion technology ; ability to generate partial power under cloudy conditions; and the modular and scalable nature of plant design. Another potential benefit of widespread CSP deployment is a much greater GHG emission offset due to the very high albedo of heliostat fields. However, this resulting change in the albedo of the surface as well as the temperature and evapotranspiration of water at a CSP deployment may have implications for local cloud cover. The extent to which such changes would reduce or increase surface warming requires a regional simulation of the cloud properties, cloud fraction, and cloud duration. While both PV and CSP technologies affect the local environment, the extent in which they do so has not been studied in detail. Nemet estimated that the low albedo of PV panels is responsible for lowering the GHG emission offset by 3% when compared with current carbon-intensive energy scenarios. As the penetration of renewable sources increases, that percentage will also increase, and perhaps to a point of being a significant hindrance to continued GHG emission offsets. Even more important, the local thermal balance effects may cause local environmental disruption in desert areas that rely strongly on the very low soil water content. Midday temperature increases of more than 3 K have been observed in desert PV plants. Conversely, heliostat fields in CSP tower plants are characterized by albedos that are 40-50% higher than the original ground albedo, commercial drying racks thus the GHG emission offset for CSP is much higher in comparison to PV technologies. Locally, a temperature reduction of 2 K and reduced rates of evapotranspiration have been observed as a direct result of the increased albedo of heliostat fields.

This Chapter aims at quantifying the albedo replacement effects of large scale solar farms mainly concerns the temperature anomaly calculated from local radiative balance of the PV and CSP surfaces.Large scale solar farms interact with the atmosphere though land surface albedo replacement. Solar PV farms are highly absorbing while CSP farms are highly reflective when compared to the ground. The spectral albedo of regular surfaces, PV panels and CSP heliostats are plotted in Fig. 6.1, where PV panels have spectral albedo smaller than 0.1 while CSP heliostats have albedo greater than 0.9 in infrared and visible bands. Among the six CIRC cases, surfaces of case 1-3, 6 and 7 have nearly the same albedo while the surface of case 4 has much higher albedo in visible and UV bands, indicating the presence of ice or snow. For the analysis of this section, the regular ground is chosen to be the surface of CIRC case 2. PV panels are assumed to be Si pillar solar cells with spectral reflectance data given by Ref.. The reflection of PV panels is assumed to be diffused. CSP heliostats are assumed to be AgGlass 4 mm Flat glass mirrors, with spectral specular reflectance data given by Ref.. All surfaces are assumed to be oriented horizontally facing the open sky. The vertical profiles of temperature, gases, aerosols and optical properties of gases, aerosols, clouds follow the methodologies presented in Ref.. Note that the effects of PV and CSP farms presented in the following sections are the ‘maximum’ effects, because in the one dimensional radiative model, the entire ground is covered by PV or CSP, but in reality, only a portion of the ground is covered.Atmospheric long wave radiation and solar shortwave radiation are essential components of thermal balances in the atmosphere, playing also a substantial role in the design and operation of engineered systems that exposed to open sky, for examples, cooling towers, radiative cooling devices and solar power plants.

To quantify the spectral thermal balances of the atmosphere and engineered systems, especially optically selective devices, comprehensive line-by-line radiative models are developed to simulate atmospheric long wave and solar shortwave radiative transfer in the Earth – atmosphere system, as well as the interactions between engineered systems and the atmosphere. Firstly, simple parametric models are developed to calculate broadband downwelling long wave irradiance at the surface. Under clear skies, fifteen parametric broadband models for calculating long wave irradiance are compared and recalibrated. All models achieve higher accuracy after grid search recalibration, and we show that many of the previously proposed LW models collapse into only a few different families of models. To account for the difference in nighttime and daytime clear-sky emissivities, nighttime and daytime Brunt-type models are proposed. Under all sky conditions, the information of clouds is represented by cloud cover fraction or cloud modification factor . Three parametric models proposed in the literature are compared and calibrated, and a new model is proposed to account for the alternation of vertical atmosphere profile by clouds. The proposed all-sky model has 3.8% ∼ 31.8% lower RMSEs than the other three recalibrated models. If GHI irradiance measurements are available, using CMF as a parameter yields 7.5% lower RMSEs than using CF. For different applications that require LW information during daytime and/or nighttime, coefficients of the proposed models are corrected for diurnal and nocturnal use. Then, an efficient spectrally resolved radiative model is developed to capture spectral characteristics of long wave radiation in the atmosphere, under clear and cloudy skies. For the non-scattering clear atmosphere , the surface DLW agrees within 2.91% with mean values from the InterComparison of Radiation Codes in Climate Models program, with spectral deviations below 0.035 W cm m−2 . For a scattering clear atmosphere with typical aerosol loading, the DLW calculated by the spectral model agrees within 3.08% relative error when compared to measured values at seven climatologically diverse SURFRAD stations.

This relative error is smaller than the aforementioned calibrated parametric model regressed from data for those same seven stations, and within the uncertainty of pyrgeometers commonly used for meteorological and climatological applications. The broadband and spectral forcing of water vapor, carbon dioxide and aerosols are quantified using the model. When aerosol optical depth equals 0.1 are considered, long wave aerosol forcing falls between 1.86 W m−2 to 6.57 W m−2 . The forcing increases with decreasing values of surface water vapor content because the aerosol bands contribute mostly when the water vapor bands are not saturated. When examining the spatial and spectral contributions of water vapor to the surface DLW, we find, as expected, that water vapor in the nearest surface layer contributes the most, especially in the spectral ranges 0 ∼ 400 cm−1 and 580 ∼ 750 cm−1 . Within the atmospheric spectral windows 400 ∼ 580 cm−1 , 750 ∼ 1400 cm−1 and 2400 ∼ 2500 cm−1 , water vapor above 3.46 km has negligible effect on the monochromatic surface DLW. In some spectral regions, there is a decrease in water vapor forcing because water vapor content in the layers below prevents the long wave radiation from reaching the surface. The warming caused by aerosols mostly comes from the layers below 3.46 km. In a narrow spectral band between 1050 to 1150 cm−1 above 3.46 km, there is a decrease in monochromatic surface DLW forcing, since the lower layer aerosols prevent the radiation from reaching the surface by absorption. Spectral and spatial distribution of irradiation is presented for an atmosphere with surface relative humidity of 65% and aerosol optical depth at 479.5 nm equals to 0.1. First order broadband contributions of increased atmospheric CO2 to surface downwelling flux is found to be 0.3 ∼ 1.2 W m−2 per 100 ppm CO2 increment for different water vapor contents. The broadband reduction of TOA upwelling flux is found to be0.5 ∼ 0.7 W m−2 per 100 ppm CO2 increment. Contributions to the irradiation on the top atmosphere layer and outer space layer come from the surface in the atmospheric window bands, cannabis grow systems from the middle of atmosphere in the water vapor absorbing bands and from the top of atmosphere in the CO2 absorbing bands. For broadband flux contributions, the outer space layer dominates the transfer factors to upper layers but the flux contribution is negligible due to low densities and effective temperatures at that level. For the ground layer, 64.4%, 15.3% and 7.5% of its long wave irradiation comes from the nearest atmospheric layer, the 2nd nearest layer and the 3rd nearest layer, respectively. And the contributions mostly from the four absorbing bands. For all layers below the tropopause, the layer itself contributes the most to its irradiation. For layers above the tropopause layer, the largest contributor to its irradiation is the ground layer. Finally, upper layers above the tropopause contribute to less than 4.8% to the irradiance flux to other layers. Then accurate correlations for the effective sky emissivity as functions of the normalized ambient partial pressure of water vapor for both broadband and seven distinct bands of the infrared spectrum are proposed. The band emissivities are correlated by simple expressions to ambient meteorological conditions at the ground level, and allow for the expedient calculation of cooling power efficiencies of optically selective materials designed for passive cooling or heating. Comparisons between band calculations and line-by-line calculations yield errors that are generally within the measurement uncertainty of atmospheric instrumentation , thus validating the combined approach of high fidelity spectral models with ground experiments taken at diverse micro-climates, altitudes and meteorological conditions.

When clouds are added to the spectral model, the representative cloud characteristics are also proposed as empirical functions for different surface meteorological conditions to guide future modeling efforts. These results enable direct calculation of the equilibrium temperature and cooling efficiency of passive cooling devices in terms of meteorological conditions observed at the surface level. The cooling potential of passive cooling materials is found to be as high as 140 W m−2 for dry and hot conditions without the presence of clouds. But the potential diminishes with increased water vapor content and the presence of clouds, because both water vapor and clouds ‘block’ the atmospheric window for cooling. A Monte Carlo line-by-line radiative model is developed for solar shortwave radiative transfer in the atmosphere, with different surfaces . The local thermal effects of albedo replacements of PV and CSP farms are quantified. Under clear skies, the downwelling GHI is being suppressed by the presence of PV farms while being enhanced by the presence of CSP farms , because of the back-scattering of reflected irradiance from heliostats. The TOA upwelling flux enhancement of CSP plant could be as high as 187%, so that CSP fields are able to cool the surface. Under cloudy skies, the GHI enhancement by CSP is amplified by the presence of clouds because multiple reflections occur between highly reflective CSP farms and clouds. By performing a surface thermal balance, the surface temperature of CSP is 3 K lower than the ambient while the surface temperature of PV or regular surface is more than 40 K above the ambient while under direct sunlight. Under cloudy skies, the irradiance and temperature modification of PV and CSP farms are reduced because the effects of clouds, especially optically thick clouds, dominant. The results presented here strongly suggest the possibility of hybrid solar plant designs that employ an outer ring of PV solar field surrounding an inner heliostat field around the central tower. This hybrid design accomplishes two important objectives: minimization of local changes in temperature and humidity by balancing out the heating caused by the PV field with the cooling caused by the CSP heliostats, and the minimization of DNI variability effects on plant operation through the coupling with the less-variable GHI component absorbed by PV panels. In addition, the thermal balance discussed in this work also allows for the consideration of dual land use, especially under the heliostat field. A raised heliostat field with partial shading may be used for agricultural purposes in desert areas where very few plants could survice without partial shade and lower temperatures and higher humidities. Note that PV panels not only increase downwelling infrared radiation to the soil, but also prevent radiative exchange with the desert sky at night, which in many regions is the mechanism that allows for the formation of dew at night. By considering these different heat and mass transfer mechanisms carefully, novel solar power plant designs may reduce their environmental impact on desertic areas.In 2006, Bagged fresh spinach from the central coast region of California contaminated by Shiga toxin-producing Escherichia coli bacteria with the serotype O157:H7 caused 199 illnesses across 26 US states, and at least 3 deaths .

The mean incidence and prevalence values were extremely low due to the fact that the model simulations assumed that only one super-shedder adult cow and another infected adult cow were introduced into the herd in pen 10 and pen 8, respectively and followed for 10 years. Similar results were obtained when small numbers of infected cows and supershedders were introduced into a herd of 10,000 cows. This indicates that the illustrated results are consistent for small numbers of infectious cows and supper shedders initially introduced to the herd. In the population of adult cows, controls 2 & 4a, 2 & 4b, 3 & 4b, 5 & 4b, 4a & 4b , and all controls combined result in a MAP prevalence of 0.52%. Measures 4a or 4b are common to all the adult cattle effective control measures. Hence an effective way to reduce MAP prevalence in the adult cow population is test and cull of test-positive cattle. However, control 4a was more effective than 4b resulting in a MAP prevalence of 0.61% and 0.98%, respectively. Table 10 shows the number of weekly incidence and the mean MAP prevalence for the most effective triple combination control measures and all of the control measures by the end of year 10 for calves and heifers were 5 & 4a & 4b ; and for adult cows is seen with 3 & 4a & 4b . Simulating all the control measures results in the mean MAP prevalence by year 10 in calves and heifers of 0.009% and in adult cows 1.04%.The simulation results indicate that no single control measure was sufficient to prevent increase in incidence of JD; however, Control 4b resulted in the best single control measure. The most effective combination of binary control measures was produced by controls 4a annual test and cull of adult cows and 4b . The overall risk of MAP occurrence was substantially reduced when test and cull was combined with intensive enclosure cleaning to reduce MAP concentration in the environment.

Particularly, the best triple control measures resulted when combining Controls 3, 4a and 4b, dry racks for weed which combined increased scraping of fecal slurry on solid surfaces in the dairy and /or power washing by 10-fold to reduce the environmental pathogen load, while also testing and culling dry-off cows on weekly basis and adult cattle annually. A farm that employs all control measures or a combination of these three control measures has the minimum risk of JD occurrence. It also has extremely prevalence and incidence provided that the number of infectious cow and supper shedder added to the herd is very small . Finally, it should be noted that these results can be expected if the dairy manager adheres to a cattle movement pattern between pens which maintains a degree of isolation between calves and cows and within the cow population as illustrated in the Cattle Movement diagram. Purposefully moving cattle between pens in a prescribed sequence changes the contact patterns between susceptible and infected cows beyond the assumption of random mixing inherent in infectious disease models. Cattle movement management is integral to the effectiveness of MAP control measures and changes to this system can modify the anticipated success of the control measures.Modeling JD with effects of vaccination has been addressed in previous works . In the present study, we did not investigate the effects of vaccination in our modeling and numerical simulations. Previous research has shown that exposure to MAP vaccines or M. aviumantigens can result in false positive tuberculosis tests, which is a concern for herds in TB free states and specifically those that commonly transport cattle across state lines. Furthermore, no vaccine has been developed to fully protect calves. There is currently no available approved treatment in food animals once an animal has contracted the MAP infection. For such reasons vaccinating against MAP is not widely practiced and hence was not considered in the current model.

In the present work we assumed that the amount of shedding in the calf population does not sustainably influence the transmission dynamics of JD, i.e., γC = 0 for pen 1 . Nevertheless, this could be oversimplifying assumption in cases that the shedding rate is greater than a critical value. Although the simulation result indicate that test and cull can be an effective control measure, there are two major concerns regarding test and cull. First, test and cull result is an immediate economic loss, which may not be recovered for a long period. Second, diagnostic tests to identify infected cows often have low sensitivities and are often costly to apply routinely. Therefore, the efficacy of test and cull substantially varies based on the frequency and sensitivity of the test. There are simulating models and field studies that aim to determine the optimal culling rate in different herds based on the long term profitability of the control measure. However, more data and model simulations are needed to develop reliable, effective and profitable JD control programs. It should be noted that the data related to this study is from California dairies. Hence, the outcomes of current study may not necessarily apply to non-intensive dairy systems elsewhere in the US and the world. However, for dairies that manage cows in housing units and groups similar to the study dairies our findings may apply in terms of effectiveness of control measures and what may be expected in reduction of MAP transmission. Another limitation of the current study as with other mathematical modeling studies and specifically those modeling MAP transmission is the lack of precise transmission rates and other inputs needed by the model. Such model inputs require specifically designed studies that can limit variability and target the specific rate of interest. However, MAP’s chronicity increases the duration of such studies which may translate to increase in cost in addition to prolonged duration of studies and potential for loss of follow up of study animals given other competing risks. To address these limitations, the current study identified several key assumptions that can be justified to utilize ranges of transmission rates from previous works .Investigating the optimal use of the cattle movement model with additional controls can benefit from these findings as the data shows that test and cull strategies seem to give the best outcome for R0. When test and cull is applied in pens 7 through 14 we see the most desirable outcome. While the primary goal of this work was to determine the efficacy of control measures using a NC model applied to JD on dairy farms, such models could also be employed to explore impacts on other animals and potentially applied to other diseases.Antimicrobial resistance is a growing concern for food safety and public health globally. Both humans and animals share similar antimicrobial drugs; hence, the judicious use of antimicrobials by both veterinary and human medicine is important to reduce the risk of AMR in enteric bacteria. The administration of therapeutic and prophylactic antimicrobial drugs in animals can be at the individual animal or at the group level. Improper or excessive use of antimicrobials can lead to the development of AMR and multidrug resistance in dairy cows and calves, which could potentially result in the accumulation of bacterial AMR genes within livestock and throughout the farm environment. Modern dairy production systems can be composed of multiple inter-connected cattle production stages, with each stage characterized by unique management practices. Production status, disease conditions, and health status within the cattle groups, and patterns of and governing regulations for antimicrobial usage vary with these stages of production. The distribution of AMR genes in dairy farm settings has not been fully characterized due to the complexity of resistome in dairy production systems and different bacterial communities for different stages of production throughout the farm environment.

According to USDA’s Animal and Plant Health Inspection Service, antimicrobial use in dairy cattle production is classified as three stages of dairy production consisting of preweaned heifers, weaned heifers, and cows and treatment of digestive problems, respiratory infections, mastitis, lameness, and reproductive problems. In general, commercial racks the most frequent antimicrobials used in dairy cattle are tetracyclines, beta-lactams, cephalosporins, and florfenicols. Excessive selective pressures with high antimicrobial concentrations of relevant enteric bacteria can result in a high probability for selection, survival, and dissemination of AMR genes in the environment . Although AMR genes are frequently detected in bacteria from dairy cattle feces, far less is known about the relative abundance of resistance in cattle at different production stages. These knowledge gaps of the ecological connectivity of AMR reservoirs in relation to their microbial communities, and AMR gene transmission pathways within and between dairy cattle at different production stages hamper our efforts to minimize the emergence and persistence of AMR. Whole-genome sequencing and bio-informatics approaches are increasingly used to systemically characterize AMR genes in bacteria from livestock including dairy cattle. The State of California has been the primary dairy producer in the US since 1993, contributing to 18.5% of US milk production. In 2017, dairy cows in California accounted for greater than 20% of the entire dairy population in the US. The overarching goal of this study was to characterize AMR genes in commensal bacteria from cattle at different production stages to generate data that can support future efforts to target AMR control efforts on the farms. Our objectives were to identify AMR genes in Escherichia coli and Enterococcus spp. from cattle at different production stages, contrast AMR phenotypes with the presence or absence of these bacterial AMR genes and identify production stages that have higher risks of spreading AMR genes within the farm environment.The purpose of our study was in part to characterize the overall resistance profile of fecal E. coli and Enterococcus from cattle at different production stages. Based on the resistance genes detected from the ResFinder database , genes conferring resistance to tetracycline, sulphonamide, and aminoglycoside were the main resistance genes in E. coli. This finding was similar to a previous study of AMR in E. coli isolated from dairy cattle, which found E. coli was mostly resistant to tetracycline followed by florfenicol , ampicillin , and chloramphenicol. For Enterococcus spp., resistance to macrolide was the main resistance gene identified in the ResFinder database . In terms of resistance genes identified from the CARD database, 100% of E. coli isolates had genes resistant to over 15 classes of antimicrobials, and 77.6% of Enterococcus isolates had genes resistant to three classes of antimicrobials. Due to the differences in availability and settings of genes between the ResFinder and CARD databases, it was not surprising that resistance genes in E. coli and Enterococcus identified from the two databases were not identical. Interesting, the two databases were consistent in the detection of tetracycline, aminoglycoside, and phenicol as major resistant genes in E. coli and macrolide and aminoglycoside as major resistant genes in Enterococcus. With respect to the major resistance in E. coli and Enterococcus , tetracycline is one of the commonly used antimicrobials in food animal production in the US and Europe, frequently for digestive conditions. Tetracycline is normally used for the treatment of respiratory diseases in food-producing animals in the US. Tetracycline-resistant bacteria, especially non-pathogenic or commensal bacteria, may play a major role as bacterial reservoirs for AMR and MDR, both within cattle populations and for the general dairy farm environment given the ubiquity of manure in these production systems. In general, macrolides and lincosamides are used for the treatment of bacterial infection, especially in mastitis cows, and for growth promotion in food-producing animals. Macrolides are also used in combination with aminoglycosides to treat mastitis in dairy cattle in some European countries, while lincosamides are mainly used in the US in dairy cattle production. We did not collect information on antimicrobial use for this study;hence, we were unable to assess the relationships between the occurrence of AMR genes and antimicrobial use on the farm. However, many studies have indicated that the use of antimicrobials in food-producing animals including dairy cows can lead to increases in AMR and MDR bacteria on livestock farms. In future studies, it would be interesting to further investigate the relationships between AMR and patterns of antimicrobial use at different production stages.Enterococcus spp. are known to cause mastitis in dairy cattle. A previous study revealed that Enterococcus spp. isolates from fecal samples from 122 dairy cattle operations were resistant to lincomycin , followed by flavomycin , and tetracycline.