Grower interviews. In 2006, late rains prevented many growers from normal spring tillage operations and a few growers were faced with the option of no spring tillage, and planting late or not planting at all. In winter 2007, we did phone interviews with three growers who did not use spring tillage in 2006 — as many as we could find. The purpose was to compare results from our relatively small experimental plots with what growers found at the field scale. Growers were asked to compare their minimum-till field with an adjacent conventional field, and to answer questions about productivity, tillage practices, and weed and fertilizer management. Growers were also asked how they would improve the minimum-till system and if they thought it was economical.Similar rice yields. The highest yield was more than 9,300 pounds per acre in 2004, and the lowest was about 7,300 pounds per acre in 2005 . These annual yield fluctuations are in line with countywide fluctuations in California and reflect climate variation. Better weed control. The minimumtill treatment was extremely effective in depleting weed populations from the upper soil layer and markedly diminishing weed emergence with the crop . When this practice was used, little weed control was needed after the glyphosate application. In fact, no additional herbicides were needed in 2004. The most important rice weed in these systems during the study period was small flower umbrella sedge . On average for the 3 years, rolling grow table the minimum-till treatment suppressed small flower umbrella sedge populations by 94%. Infestations by the aquatic rice field bulrush also became relevant in 2006, and were 91% suppressed under the minimum-till treatment . Water-seeding rice strongly suppressed both barnyardgrass , the main Echinochloa species in this field , and sprangletop .

However, Echinochloa spp. populations became somewhat higher in the last year of the experiment, and the minimum-till treatment also exhibited potential for suppressing this weed. Success with the stale seedbed technique depends on keeping the seedbed moist or highly saturated, depending on if aquatic weeds are present, and allowing sufficient time for weeds to emerge prior to the glyphosate application. In 2006, there was neither sufficient seedbed moisture nor sufficient time for substantial weed emergence. Consequently, few weeds were present when the glyphosate was applied. Even so, the minimum-till treatment was successful in controlling weeds, suggesting that leaving the soil undis-turbed in the spring helped discourage weed emergence. While the stale seedbed technique worked well when enough weeds had emerged prior to the glyphosate application, the late-emerging aquatic weeds ducksalad and redstem/redberry were not well suppressed ; in fact, ducksalad became an increasing problem over time in the minimum-till treatment.There were no differences in rice water weevil levels between the conventional- and the minimum-till treatments in a given year, although there was a trend toward more weevils with minimum tillage. The weevils were present at low levels in all plots in 2005 and 2006. The incidence of adult feeding scars was higher in 2005 than 2006, with 15% and 7% of plants scarred, respectively. Likewise, larval densities, which peaked at 0.2 per sample in 2006, did not differ between the two treatments in any given year.When no nitrogen fertilizer was applied, the minimum-till treatment had smaller yields than conventional tillage . This is probably because minimum tillage had two flooding events while conventional tillage had only one. When soil is flooded and then drained, nitrate accumulates during the aerobic period but may be subsequently lost through denitrification during the following anaerobic period . In response to added fertilizer, the results varied between years but suggested that minimum tillage requires more nitrogen than conventional tillage to reach similar yields.

In 2004, the minimum-till treatment required three times as much nitrogen as the conventional-till treatment to achieve optimal yields . In contrast, in 2006 similar nitrogen rates in the two till systems resulted in similar yields. Splitting the nitrogen fertilizer dose has previously been shown to increase its use efficiency . However, that was not the case in the nitrogen fertility trial portion of this study. Splitting the 150 pounds of nitrogen per acre in 2004 did not affect yields. This may be because this nitrogen rate exceeded that required for optimal yields, masking any increases in use efficiency. Splitting the 100 pounds of nitrogen per acre equally in 2006 actually resulted in lower yields than a single application of this rate at planting. However, it is possible that higher yields would have resulted from an unequal split, such as 75 pounds of nitrogen per acre at planting and 25 pounds per acre 40 to 50 days after planting. The nitrogen fertility experiments were not conclusive, and further research is warranted. However, some general conclusions can be drawn based on our results. First, the additional flush of water in the minimum-till system will likely result in the loss of native soil nitrogen. Second, nitrogen fertilizer in the minimum-till system is applied to the soil surface, where it is used less efficiently . Both of these factors suggest that the minimum-till system will require a higher nitrogen rate to maintain yield levels. While we can not determine a precise rate from our data, it appears that minimum tillage requires approximately 50 pounds of nitrogen per acre more than conventional tillage. This is based on the 2004 response and the fact that in both years the zero nitrogen yields were lower in the minimum-till treatment, which suggests a loss of native soil nitrogen.Three growers were interviewed who established rice using water seeded practices in 2006 onto fields where there had been no spring tillage . In all cases, the growers incorporated rice straw or stubble in fall 2005 either by disking or wet rolling. Winter flooding varied between the fields but due to a wet winter, all were flooded for at least a portion of the winter. Growers 1 and 2 used a modified stale seedbed in which late spring rains germinated weed seeds and glyphosate was used to kill the weeds before flooding the field to plant.

Grower 3 aerially broadcast rice seed into water from the winter flood period and drained the field shortly after planting. In all cases, nitrogen was applied aerially in three to four applications. Total nitrogen was comparable to what each grower normally applied and ranged from 140 to 210 pounds per acre. One issue raised by the growers was fertilizer management, specifically how and when to apply nitrogen and phosphorus. Results from the on-station study suggest that only one or two nitrogen fertilizer applications are necessary. Also, phosphorus should be applied in the fall and incorporated because surface phosphorus applications may result in an algae problem, which grower 2 experienced. Despite the late spring rains, all three growers were able to plant early, before May 3 . These were the first planted fields in their respective areas, and as a result, growers reported some rice seed predation by ducks. While two of the three growers used slightly higher seeding rates than the recommended 150 pounds per acre, data from the on-station experiment suggests that this may not be necessary. Two of the three growers reported that yields from their minimum-till fields were comparable to or better than their other fields. However, vertical grow system grower 3 reported that yields were about 600 pounds less per acre. These lower yields may have been due to phosphorus deficiency since none had been applied, although this grower typically did apply phosphorus fertilizer. A second possibility for this lower yield is that rather than draining the field following the winter flood, grower 3 retained winter flood water until after planting, which may have lowered soil oxygen levels and resulted in poor crop establishment. The predominant weed species found in the minimum-till fields were similar to those typically found by these growers , and the severity of the weed problem was similar to or less than normal. The two growers using a stale seedbed reported that the rains germinated weeds, which they were able to kill with glyphosate. All growers reported that either lower rates of herbicides, fewer applications or a different program was used on their minimumtill fields. On-station research showed that the stale seedbed system was able to control much of the weed problem . However, research is needed to better understand how long soils should remain moist or flooded and what temperatures are required to germinate specific weed seeds.All three growers interviewed reported that the economic benefits of minimum tillage were similar to or better than their conventional-tillage practice, and some said they might try it again. The main reason was that minimum tillage resulted in six to eight fewer tractor passes, which amounts to a fuel and labor savings of $120 per acre . However, some of these savings were offset by the additional air passes required to apply glyphosate and fertilizer. Based on research from the on-station experiment, growers could apply fertilizer once or twice instead of the three to four times that they reported. Growers also indicated that if they were planning on no spring tillage, they would do more tillage in the fall, which would further offset the economic benefits. In addition to possible economic benefits, one major benefit was that growers were able to plant early despite late rains. One drawback of the minimum-till system is the increased amount of nitrogen required to maintain yields. Since nitrogen must be applied on the surface, it is more susceptible to denitrification losses. This can have the effect of reducing the economy of these systems and increasing emissions of nitrous oxide, a greenhouse gas.In both on-station research and grower fields, the minimum-tillage system maintained rice yields in the absence of spring tillage. Where does minimum tillage fit in to a grower’s overall farm-management strategy? First, minimum tillage can be useful when late spring rains prevent early planting under conventional tillage practices, as in 2006. Second, growers could employ minimum tillage to plant fields early. In such cases, additional tillage and phosphorus and potassium applications would be recommended in the fall. Finally, minimum tillage can be used to control herbicide-resistant weeds by germinating weeds and subsequently killing them with glyphosate, an herbicide to which California’s rice weeds are not yet resistant. Soil moisture must be carefully monitored and controlled because weed species require varying wet periods and temperatures for germination; this is an area of ongoing research. While glyphosate can currently control all types of California rice weeds that are resistant to other herbicides, glyphosateresistant weed biotypes have evolved in areas of California where this herbicide has been used for many years . Therefore, glyphosate should be alternated with other herbicides, such as paraquat and glufosinate-ammonium, that are also lethal to herbicide-resistant rice weeds .

Within each quadrat, we determined the identity and percent cover of all species present. We also recorded the percent cover of bare ground, water, and thatch . In addition, we estimated the number and percent cover of germinating seedlings for native species. Because lowgrowing graminoids and forbs were often overlaid by taller species, the total percent cover could exceed 100% in each quadrat. To measure the pool area, we used a Trimble GPS to map out the perimeters of each pool. We used a laser level to measure the depth of each pool. We obtained climate data from the National Oceanic and Atmospheric Administration Daily Summaries dataset for the Santa Barbara Municipal Airport weather station to calculate the average annual rainfall each pool experienced after it was restored .The 69 pools surveyed in this study were restored between 1986 and 2017. The pools all shared similar attributes in terms of past and restored abiotic and biotic conditions, so we constructed a chronosequence that used a space-for-time substitution to examine the effect of time since restoration on native and exotic cover and richness. Past restoration actions included grading and berm enhancement to attain basin topography with an area ranging from 66 to 1,367 m2 and a maximum depth ranging from 53.5 to 80 cm, planting of locally-sourced native plant species via seeding and transplanting, and hand-weeding and herbicide treatments of exotic species during a 2- to 5-year implementation phase . In the spring of 2019, we conducted vegetation surveys in each pool when the majority of the native species were at peak biomass. For each pool, we laid out 2 transects bisecting the pool along its elliptical major and minor axes . Every other meter along each transect, grow room we laid down a 1 m2 quadrat with 1% subdivisions. We identified every plant species present and estimated its percent cover in each quadrat. We also estimated the percent cover of bare ground and thatch. Because low growing graminoids and forbs were overlaid with taller species, the total percent cover could exceed 100% in each quadrat.

We also categorized each quadrat as being in the central, transition, or upland zone of the pool. To measure relative elevation, we used a laser level to calculate the elevation of each quadrat above the deepest point of the pool. To determine pool hydroperiod, we installed 0.8 m rulers in the deepest part of each pool in January 2019 and recorded the depth of the water in each pool every week beginning 11 January until all the pools dried up by 5 July. To measure the site and pool area, we used a Trimble GPS to map out the perimeters of the sites and the pools. We also used these data to calculate each pool’s perimeter-to-area ratio and the distance of each pool from the edge of the restoration site. We obtained climate data from the National Oceanic and Atmospheric Administration Daily Summaries dataset for the Santa Barbara Municipal Airport weather station to calculate the precipitation each pool experienced the year before restoration began, the precipitation each pool experienced the year that restoration began, the precipitation each pool experienced the year after restoration began, and the average annual precipitation each pool experienced after restoration began .For each quadrat in each sampling year, we calculated the maximum monthly exotic plant species percent cover, total exotic plant species richness, maximum monthly native plant species percent cover, and total native plant species richness. The exotic species cover distribution was skewed right as determined by histogram and Q–Q plot analyses, so we used raw data to construct a generalized linear mixed effects model with a gamma distribution, using a logarithmic link function. The exotic species richness and native species richness distributions were not normally distributed as determined by histogram and Q–Q plot analyses, so we used raw data to construct a generalized linear mixed effects model with a Poisson distribution. The native species cover distribution was normally distributed according to histogram and Q–Q plot analyses, so we used raw data to construct a linear mixed effects model.

All four models were predicted by the age of the pool during each sampling year and the zone , and the interaction thereof, as fixed effects, with sampling year, quadrat name , pool depth , pool area , and average annual precipitation included as random effects.The increase in exotic cover and richness in our multiyear monitoring study suggests that short-term restoration efforts do not guarantee long-term success in the transition and upland zones of restored pools. The pools in this study were created and planted with native species within a grassland landscape. Intensive exotic species weeding continued for about 2–5 years after each pool was created, but then the pools entered the maintenance phase and were only periodically hand-weeded or cleared with a weed-whacker. Although the initial intensive weeding kept exotic cover low, exotic cover increased in the transition and upland zones over time. This suggests that the initial weeding successfully reduced exotic species, which is why exoticcover remained low for several years after the implementation phase. However, without continual removal, recruitment from exotic populations adjacent to the restored pools allowed for eventual recolonization of the site. Previous studies have shown that restored native populations can subsequently decline and even go extinct due to low growth rates that are negatively affected by interannual environmental variability and competition by invasive species . Indeed, other long-term monitoring studies in other ecosystems, such as grasslands and forests, have also shown that restored plant communities never reach the species diversity of natural reference ecosystems . Our study adds to a growing body of evidence that short-term restoration projects do not guarantee the long-term persistence of diverse native assemblages. Our results indicated that exotic plants invaded pool transition and upland zones, but not central zones, suggesting that invasion into the pool edges comes from the surrounding invaded grassland matrix. Invasive exotic species are often unsuccessful in the central zones because of their inability to tolerate prolonged inundation . However, increased drought due to climate change may result in drier conditions even in the deepest parts of pools, perhaps making the zone less hospitable for vernal pool specialists and more susceptible to natural recruitment by invasive species .

Although restoration efforts may plant and establish native populations within a vernal pool, the surrounding landscape often consists of unrestored grassland invaded by exotic grasses, which may contribute many propagules to pool edges. In addition, once propagules establish in the pool, positive feedbacks such as litter build-up can cause exotic populations to invade and persist . These edge effects are common throughout restored ecosystems . Small-scale restoration projects, which typically occur amidst fragmented habitat in the form of patches, can be susceptible to edge effects due to stressful environmental conditions and disturbances originating outside of the habitat patch . For example reinvasion of Phragmites australis from the surrounding landscape into wetlands is common, as is the encroachment of trees from forests into adjacent meadows . Several studies have shown that exotic species abundance increases closer to forest edges, where disturbance and exotic propagule supply is high . It is, therefore, critical to evaluate and manage edges of restoration projects as they face unique pressures that can jeopardize native assemblages.Our results highlight the importance of both sustained inundation of central zones and active management of transition and upland zones of vernal pools to reduce invasion. Collinge et al. have similarly emphasized the role of both abiotic and biotic filters in creating and sustaining restored native communities that are resistant to exotic invasion . Biotic filters that can decrease susceptibility to reinvasion include adaptive management strategies, such as planting with competitive native species and active control of exotic competitors through an array of long-term weed management techniques . In vernal pools, drying cannabis strategically planting suites of species at different elevation zones within pools can also increase native establishment and persistence. For example, in our studies, E. macrostachya, J. mexicanus, and J. phaeocephalus were able to dominate the central zone, while Carex praegracilis, E. macrostachya, Distichlis spicata, J. mexicanus, and E. triticoides performed well in the transition zone, and Stipa pulchra, Cyperus eragrostis, and Hordeum brachyantherum were able to establish and persist in the upland zone despite exotic invasion, so these species can be the foci of zonal planting palettes for future local restoration projects. Although intensive hand-weeding did not create resistance in the edges of the pools and may not be sustainable in the long run due to time and resource constraints, feasible long-term weeding strategies may focus more on large-scale contexts. For example, the upland and surrounding unrestored grassland matrix probably accounted for the exotic invasion of the transition and upland zones of the pools, so large-scale grassland management techniques such as grazing and prescribed fire disturbance may reduce exotic species dominance in both the grassland and the edges of the vernal pools . Even periodic reductions of exotic species could help to sustain greater native abundance in the edge zones. Overall, our studies evaluating the trajectories of plant assemblages post-implementation suggest that active management of restored habitats should persist beyond the implementation phase, which means projects need to be budgeted with long-term monitoring and adaptive management plans. Although 5 years of intensive restoration efforts can successfully reestablish native assemblages, our studies showed that native cover and richness decreased significantly in older pools. Other studies of restored wetlands similarly showed that restored wetlands initially achieving high native plant diversity can subsequently experience a decline in native diversity and an increase in exotic diversity 5–11 years post-implementation . Our long-term monitoring dataset provides unique insight into plant community trajectories over time by showing that, even when central zones of restored vernal pools can remain native-dominated, the drier pool edges exposed to the surrounding exotic grassland matrix can experience reinvasion over time, much like how forest edges and other edge habitats can experience reinvasion when not actively managed . Short-term success can be misleading, and long-term monitoring is important to evaluate the success of restoration and guide adaptive management over time. Identifying drivers of reinvasion can be particularly useful for guiding adaptive management. In our study, the main abiotic variables that correlated with increased exotic diversity and/or decreased native diversity were the amount of edge area, relative elevation, and precipitation. For example, less precipitation during restoration implementation can correlate with higher exotic richness, although a wet year before restoration may promote higher exotic cover and lower native cover in the upland zone, perhaps due to competition from exotics taking advantage of higher winter water resources . Although the precipitation that a restoration site experiences cannot be manipulated, knowing whether it is a particularly wet or dry year at a restoration site can inform management decisions, e.g., resources should be allocated to weeding exotic species out of pool edges during wet years. In addition, the invasion front of vernal pools may be reduced by creating circular pools with less edge area exposed to the surrounding exotic grassland matrix and associated edge effects. Because surrounding invasive grassland populations contribute propagules that invade pool edges, restoration efforts can also prioritize creating or restoring vernal pools in smaller grassland sites with fewer invasive species. For example, vernal pools may be constructed in smaller green spaces within urban areas that are traditionally deemed too small for other habitat restoration projects. However, manipulation of these abiotic environmental variables alone cannot be relied upon to maintain high native cover and low exotic cover, especially in the higher-elevation transition and upland zones that are more hospitable to generalist species. These edge zones experienced an increase in exotic diversity and/or a decrease in native diversity over time, possibly due to the overwhelming propagule pressure from the surrounding unrestored grassland. These propagules likely take advantage of the higher-elevation edge zones of the vernal pools that, when not seeded with native species, provide hospitable open niche space for generalist grasses and forbs to inhabit . Other studies have shown that abiotic manipulation can lead to incomplete restoration, especially in hospitable environments that are easily colonized by exotic species . Sengl et al. showed that retired farmland passively restored to grassland did not achieve the same native species richness as reference sites and were instead colonized by invasive grasses.

Kay found that Hardinggrass tolerates fire, making it a good candidate for erosion control. However, the California Invasive Plant Council has listed Hardinggrass as an invasive, non-native plant that threatens wildlands. In the 1960s, summer-dormant orchard grass did well in many test plots around the state and became part of perennial grass seeding recommendations. Several other grasses, including smilograss, tall wheatgrass , and mission veldtgrass , were also recommended. Recent releases of summer-dormant tall fescue varieties are currently showing promise as a companion with summer-dormant orchard grass. Except for poor rainfall years, weed management prior to sowing perennial grasses is the greatest factor for successful establishment. Annual grass competition during establishment of perennial grasses can cause complete failures of perennial grass seedings.Native grasses, especially California needlegrass , were tested along with the introduced perennial grasses and are included in the recommendations by Love et al. . Restoration of native grasses has been a recurring objective of range managers on California’s annual rangelands since the 1940s. The goal of restoring grasslands and woodland understories to some presettlement condition has proven to be unrealistic, because not only is there uncertainty about the historical composition and extent of California native grasslands, but restoration failure is common. Rangeland and restoration scientists have tried to restore native grasses but have not found dependable native grass restoration practices for use on land that is steep, rocky, hydroponic rack system or highly eroded. Competition from naturalized annual grasses and forbs remains a major barrier to native grass restoration. Season-long heavy grazing has also resulted in poor stand survival.

Proper grazing of perennial grass stands is discussed in the eighth publication of this series, “Grazing Management.” On arable land, native grasses can be grown for seed and pasture following standard crop production practices. Scientists continue to seek practices to control the annuals and promote native perennials.Annual rangeland soils without legumes are nitrogen deficient . To increase winter forage and total production, nitrogen must be added by a legume or nitrogen fertilization. Phosphorus and sulfur deficiencies are also widespread. In some areas, molybdenum deficiencies are quite common. Deficiencies of potassium, boron, and lime occur on acid soils but are not widespread. Usually these latter deficiencies become evident only after adequate amounts of phosphorus and sulfur have been applied on legume pastures. In the 1950s and 60s, the effects of nitrogen, phosphorus, and sulfur on forage production were estimated on several annual rangeland soil series using greenhouse pot studies as well as field plots . These studies showed that most soil series responded to phosphorus and/or sulfur as well as nitrogen.For about 15 years in the 1950s and 60s, University of California at Davis researchers studied the effect of nitrogen fertilization on range forage production and animal productivity on 28 ranches in 20 counties . When analyzed together, fertilizer effects the first year increased carrying capacity from 38 head days per acre to 92 head days per acre and livestock gains from 60 pounds per acre to 170 pounds per acre. Greater first year benefits were observed where nitrogen plus sulfur or nitrogen plus phosphorus were required than where only nitrogen was needed. Second-year carryover effects measured at 13 locations were much greater where nitrogen was applied with either sulfur or phosphorus than from nitrogen alone .

Table 6 is a comparison of the 1957 costs and returns, reported by Martin and Berry in 1970, with projected costs and returns in 2012. In 2012, fertilizer costs for nitrogen, depending on the formulation, were 2 to 5 times higher than in 1957 and stocker cattle prices were 5 to 6 times higher. In the mid-1980s, nitrogen was again shown to be beneficial in a large-scale study of the effects of fertilization and legumes on beef production at the UC Sierra Foothill Research and Extension Center, northeast of Marysville, California . In this study, nitrogen was applied at 40 and 80 pounds/ acre with and without phosphorus and sulfur. Phosphorus and sulfur were applied at two rates with and without nitrogen, phosphorus at 30 and 60 pounds/acre, and sulfur at 33 and 66 pounds/acre. This study showed that animal weight gains were greater with nitrogen than without and that the greatest gains resulted from application of nitrogen, phosphorus, and sulfur. This study also showed that dry matter digestibility was increased. One of the most important benefits of nitrogen fertilization is that it can substantially increase production during the winter and early spring . This early feed is extremely valuable because it replaces expensive hay or other energy supplements for livestock. For ranchers dependent on annual rangeland for winter and spring feed, the onset of the green season is awaited with great urgency each year. Nitrogen fertilizer can increase winter forage production before the spring flush of growth and effectively replace 2 to 6 weeks of supplemental feeding during the winter. Nitrogen fertilization will also increase spring feed, but this is usually not a forage-short season for the range livestock producer in California.Knowledge of range sites and their forage productivity and response to fertilization is critical in making the decision to fertilize annual rangeland. Productive sites should receive priority for fertilization. Range forage response to fertilization varies with prevailing weather patterns .

During a favorable weather year, above-average forage productivity is further increased by application of nitrogen . Likewise, low productivity during an unfavorable year can be increased by fertilization but not to the levels expected under favorable weather conditions . However, the percentage increase may be greater than in a wet year. To properly assess the response to fertilization on a given range site, the site’s forage productivity and fertilizer response during a favorable, average, and unfavorable weather year should be estimated to allow the decision maker to better assess fertilization benefits and risks over the range of weather patterns characteristic of California’s Mediterranean climate. A favorable year in terms of forage production can result from fall rains coinciding with warm fall temperatures or from extended warm, wet spring weather. An unfavorable year results when the fall rainy season is delayed or when cold fall temperatures occur earlier than normal. Most years are intermediate to these favorable and unfavorable extremes . Table 7 and fig. 12 illustrate the estimated annual forage production for a favorable, average, and unfavorable year on a range site of average productivity in the California annual rangeland. Included are expected and possible productivity improvements based on numerous fertilizer trials. Tables 8 and 9 show the combined results of 54 grazing trials designed to evaluate the effects of nitrogen fertilization over a 15-year period in 20 counties . Factors other than prevailing weather contribute to the inherent productivity of the range site. Those sites that have inherently low productivities may respond to range improvement, but the response may not be great enough to pay for the cost of improvement. Range fertilization frequently produces a 1½-to-2-fold increase in dry matter production. A site normally averaging 1,500 pounds of dry matter per acre will yield an additional 1,500 pounds from nitrogen fertilization and there is a reasonable chance that this improvement is economically feasible. If the average productivity is only 500 pounds per acre, cannabis vertical grow system then the economic feasibility of a 2-fold increase, or 500 additional pounds of forage per acre, is less likely. Range economists often advise ranchers to improve those range sites with the highest potential first. This is good advice except where the lower-potentialsite improvement has strategic value or an exception is known through past research or experiences. Additional benefit from nitrogen fertilization may be achieved by using nitrogen application as a method of manipulating livestock utilization of the range. Although it is not widely practiced, it has been shown that use of underutilized range forage can be increased by applying nitrogen and other fertilizers to that forage . Once the livestock find this area of application, they seek it out and use it to a greater extent than before it was fertilized. Similarly, it has been shown that the application of nitrogen to weed infestations can increase their utilization. If the utilization of medusahead and immature summer annuals such as yellow starthistle and tarweed is increased and grazing is properly timed, it can reduce flowering and seed set of these weeds.Ammonium sulfate , ammonium phosphate sulfate , and urea are most frequently applied on annual rangeland.

Ammonium sulfate is frequently used because sulfur deficiencies are widespread on annual rangeland, and it is less expensive than 16-20-0 containing both sulfur and phosphorus. Where sulfur and/or phosphorus are deficient, application of these nutrients should be considered. When the soil contains adequate levels of phosphorus and sulfur, urea may be used. Nitrate nitrogen tends to leach too rapidly, and it is often lost early in the first year before it can be utilized by the forage plants. Although urea is an inexpensive nitrogen source, volatility losses can reduce its effectiveness if soil pH is greater than 7 and if applied too early in the fall when soil temperatures are still high. To avoid volatilization, rainfall in excess of ¼ inch is necessary for urea soil incorporation, and greater than ½ inch is desired. A worst-case scenario is an early fall rain of less than ¼ inch that breaks down the prills but does not carry the urea into the soil. Chicken manure and other manures can be satisfactory sources of nitrogen where transportation and spreading costs do not prohibit their use. Manures are longer-lasting nitrogen sources because the nitrogen is released slowly as the organic matter decomposes. Soil and tissue testing can help to answer the question of what nutrients to apply in addition to nitrogen. Commercial agricultural testing laboratories can conduct needed soil and plant tissue tests at very low costs.In the 12-to-30-inch rainfall zone, nitrogen is generally applied in the fall to lengthen the green feed period by increasing winter growth. The amount and distribution of rainfall, as well as temperature, are principal factors governing the timing of application. Nitrogen is not profitable in central and southern California, where annual rainfall is less than 12 inches annually, because reduced soil moisture restricts plant growth and response to fertilizers. Research at the Hopland Field Station, where nitrogen was applied monthly from September through January in a 36-inch rainfall zone, showed that the earlier nitrogen was applied in the fall, the greater the winter forage growth . Total forage as measured at the end of the growing season was not affected by the time of application unless the application was made after February. Nitrogen is generally not recommended where rainfall is greater than 30 inches, since leaching losses are high. Denitrification can contribute to nitrogen losses, especially on poorly drained soils that are saturated for extended periods. Winter temperatures averaging much below 50ºF severely limit responses to nitrogen fertilization. Daily mean temperatures below this limit are common in northern California and Oregon during the months of December, January, and February. Therefore, nitrogen should be applied before the first autumn rains when mean temperatures are 50ºF or more. Lack of response in cold weather is mainly a simple restriction of plant growth, but nitrogen-fertilized grass often is less damaged by frost and appears to recover faster than nitrogen-deficient grass. Nitrogen should not be applied to ground covered in snow, as much of the snow may be lost to evaporation along with the applied fertilizer.Generally, a good forage response is gained from applying between 40 and 80 pounds/acre of nitrogen. To apply 80 pounds of nitrogen would require application of approximately 400 pounds of ammonium sulfate or 160 pounds of urea. The variation in recommendations between counties is a reflection of year and range site differences, especially annual variation in amount and distribution of precipitation. How much nitrogen to apply has been a continuing question and the subject of numerous fertilizer trials. Rates of nitrogen up to 200 pounds/acre have been applied and forage or animal yield measured. Production functions for nitrogen fertilization follow the law of diminishing returns. Therefore, beyond a certain level, each additional increment of fertilizer will give less production than the previous increment. On California annual rangelands, this point is commonly in the range of 40 and 80 pounds/ acre, and it will vary within this range due to seasonal and yearly variations in weather.

Many other growth and habitat characteristics of horseweed and hairy fleabane are similar. However, field observations in the Central Valley show that hairy fleabane produces flowers and seeds at least 2 weeks earlier than horseweed.Horseweed and hairy fleabane seem to prefer lesser disturbed soil environments. In the U.S. Midwest and other parts of the world where growers have converted or are converting to reduced-tillage systems, the prevalence of horseweed and hairy fleabane is increasing . It was found that even minimum tillage of the soil in spring or fall effectively controlled horseweed . This explains why these weeds are observed more in undisturbed situations, such as orchard and vineyard berms, field margins, roadsides, and irrigation or ditch banks in California. In Australia, these species are considered the most difficult weeds to control in no-till systems . The longevity of horseweed seeds does not seem to be very long. Seeds stored under dry conditions or in the laboratory had longevity of only 2 to 3 years . Similarly, the seeds of hairy fleabane survived up to three years under field conditions . However, a study reported viable seeds of horseweed were found in the seedbank of a 20-year old pasture despite its absence in the vegetation . The seeds of these species do not seem to have a dormancy requirement to germinate . Once the seeds are mature, they germinate as soon as conditions are favorable. This probably explains why recently dispersed seeds of these species emerge where postharvest irrigation water is applied in certain orchards and vineyards.Very little data exists on crop yield and quality losses caused by horseweed and hairy fleabane. In Michigan,vertical farming supplies it was found that horseweed reduced soybean yields by up to 83 percent . However, horseweed and hairy fleabane can compete directly with young trees and vines for soil nutrients, water, and light.

They can reduce tree and vine vigor, especially in newly planted fields. In walnut orchards in California, for example, heavy competition from these weeds can reduce tree height the first year by a foot or more. In cases such as this, growers must either replant or live with a reduced canopy height, which can make it difficult for harvesting equipment to enter the field without injuring low-hanging branches. Horseweed is also known to be a host plant for the glassy-winged sharp shooter . These weeds can form dense stands that interfere with the distribution of water, particularly in low-volume sprinkler and drip irrigation systems. These weeds also seem to be an aesthetic nuisance both in agroecosystems and natural or man-made landscapes. Horseweed can be a major problem in vineyards. If not adequately controlled, horseweed will grow through the vine canopy, interfering with harvest and other field operations . Horseweed may be particularly troublesome for raisin growers who use a continuous tray harvest system. In this system, green grapes are harvested mechanically and are spread on long sheets of paper to dry. Invariably, some berries are damaged by the harvester and release juice that can coat the berries and make them sticky. At the same time, horseweed seeds shatter on contact with the harvester, and the dislodged seeds may adhere to the surface of the sticky berries. As the berries dry into raisins, the seeds may be enveloped by the folds of raisin skins.Since horseweed and hairy fleabane seeds do not survive for more than a few years under field conditions, controlling plants before they produce new seed is critical for long-term management. Therefore, control tactics should be employed when these weeds are young and more sensitive to chemical and non-chemical controls. As these weeds begin to grow upright, their woody stem makes control very difficult and expensive.

In home gardens and areas with sandier soils, these weeds can be easily uprooted by hand.Preemergent and postemergent herbicides can provide effective control, depending on crop or location used, method of application, rate, application timing, uniformity in soil and weed wetting, and other important factors. Several herbicides used in California are effective on horseweed and hairy fleabane . As with all pesticides, follow all label recommendations closely to achieve desired efficacy and crop safety. Since a large complex of weeds is often present at any given time, applying combinations or sequential treatments of different preemergent and post emergent products is usually needed for the best overall control. For preemergent herbicides to be effective, they need to be applied uniformly to the soil surface before these weeds emerge in late fall through early spring. Control with preemergent herbicides can be reduced if they are applied to soils covered with leaves, weeds, and other debris. Removing debrisfrom the soil surface in an orchard or vineyard before applying preemergent herbicides helps maximize control of horseweed, hairy fleabane, and other weeds. If small weeds are present at the time of application, adding an appropriate post emergent product to the tank can kill those weeds as well. Soil moisture is important for the activation of these herbicides ; timing the application of a preemergent herbicide as close as possible to rainfall or incorporating the herbicide by irrigation is necessary for improved efficacy. Horseweed and hairy fleabane can also be effectively controlled with post emergent herbicides. However, it is extremely important to treat these weeds when they are very young and to apply the appropriate herbicide label rate. Tank-mixing more than one post emergent product often provides the best overall control, especially if other weeds are present. The most consistent control will be achieved when horseweed and hairy fleabane plants are treated prior to the 14-leaf stage. Once they reach the rosette stage, regrowth often occurs following post emergent treatment. Furthermore, bolted plants have woody stems and form dense canopies, making wetting of the entire plant foliage difficult and reducing the effectiveness of control.

In general, applying post emergent herbicides in a spray volume of 30 to 50 gallons per acre provides adequate wetting of the weed foliage necessary for good control. This is especially important where contact-type herbicides are used. Older and larger horseweed and hairy fleabane plants are more tolerant to systemic herbicides , and thus, treating small plants significantly improves control. Repeat applications may be required due to the extended germination period of horseweed and hairy fleabane.In cases where soil tillage is allowed, control can be achieved without the use of herbicides. Various forms of cultivation are available for both annual and perennial cropping systems. Specialized in-row cultivation equipment such as the hoe plow, in-row roto-tiller, spring hoe weeders, and berm rakes are available for certain orchard and vineyard systems that can provide effective control of these and other seedling weeds. As with herbicides, it is important to use mechanical tools when these weeds are small and most easily controlled. Mowing is not generally a viable option for control of horseweed and hairy fleabane. Mowing tends to stimulate additional branching from the crown and only delays seed production. Mowing also hardens off these plants, vertical weed grow making control with post emergent herbicides nearly impossible. Some success has been achieved with repeated applications of propane flaming, but only with plants at the seedling stage. With current and potential air quality issues in the Central Valley, flaming may not be a practical option in the future.Very little information is available on biological control of these two weed species. Since both weeds grow on lesser-disturbed and managed natural ecosystems, their seeds can easily blow into agroecosystems. Therefore, it is important to find methods that prevent the continuous influx of new seeds from the natural ecosystems. The bacterium Pseudomonas syringae pv. tagetis has been reported to affect these weeds , but this has not yet been developed as a large scale bio-control agent. Similarly, certain stem borers and leaf-eating caterpillars have been observed to damage these plants, but very little information is available on the success of these insects in controlling these weeds.Glyphosate-resistant horseweed was first discovered in Delaware in 2000 . Since then it has spread to 16 states in the United States and has also been reported from Brazil, China, Spain, and the Czech Republic . Rapid seed dispersal, the expansive use of glyphosate, and the lack of tillage are major factors contributing to the quick invasion of glyphosate-resistant horseweed in the eastern United States . In other parts of the United States, glyphosate-resistant horseweed has been reported where glyphosateresistant crops have been used in conjunction with no-till production systems . In California, glyphosate-resistant horseweed has been reported in orchards, vineyards, roadsides, and canal banks . Worldwide, including several regions of the United States, horseweed has developed resistance to several different herbicides, such as glyphosate, paraquat, and atrazine . Similarly, glyphosate-resistant hairy fleabane has recently been reported from Spain and South Africa . Confirmed cases of glyphosate-resistant horseweed and hairy fleabane were reported in California in 2005 and 2007, respectively. In California, it was observed that the foliage of horseweed or hairy fleabane would initially show symptoms of injury to glyphosate, but the plants would recover in a few weeks and survive .

Even within the same population, portions of the population were controlled while others would survive the glyphosate application . Such observations are characteristic signs of herbicide resistance. Relying on a single herbicide or combination of herbicides year after year increases the likelihood of selection for resistant populations. Rotating other effective products or using tank mixes of products where possible helps prevent or delay herbicide resistance. For detailed information on herbicide resistance management, refer to the Prather et al. 2000.In order to use straw bales as a growing medium, they must first be prepared for plant use. This preconditioning process is a form of composting. During preconditioning the bales will become hot, and the pH will change as decomposition occurs. It is important to complete the initial compost process prior to planting into the bale or plants may be injured. Microorganisms will attempt to break down the straw bales as soon as the bales are moistened. During this process nutrients—primarily sources of nitrogen—will be tied up by the microbes as they decompose the straw. As a result, plants growing in root-zone environments high in carbon, such as straw bales, may not have essential nutrients available for growth, even if fertilizer is applied, until the straw has sufficiently decomposed.For optimal composting, a ratio of carbon to nitrogen of 30:1 should be present; however, on their own, straw bales have ratios ranging from 40:1 to 100:1. As a gardener adds fertilizer containing nitrogen, the ratio approaches the ideal. Active composting will then begin. This composting process generates carbon dioxide and a substantial amount of heat. A fresh, 3-string straw bale can exceed 140°F during conditioning. Older, seasoned bales may not exceed 100°F , but should still be preconditioned before use. Once the preconditioning is complete, nutrients will no longer be sequestered in large amounts and the bale will remain cool enough to plant.Select clean, weed-free straw bales to minimize future weeding. Straw bales are usually available at farm supply dealers or directly from local farms. 2-String or 3-string straw bales may be used. Place bales with the baling twine parallel to the ground. The twine will help to hold the bale together as the season progresses and the bale decomposes . The preconditioning process begins when the bale is moistened. High nitrogen levels are maintained initially by adding fertilizer. Midway through the conditioning process, nitrogen fertilizer inputs are tapered off as the bales continue to compost. Tables 1 and 2 provide two common preconditioning schedules. The process should take approximately 2 weeks to complete for either schedule. Throughout the conditioning process, bales should be kept wet. A finger inserted in the side of the bale should feel hot and damp. It is best to add water slowly to each bale to minimize runoff and to ensure that the fertilizer applied to the surface is moved into the bale. In Europe straw bales were originally preconditioned using solid, granular fertilizers; however, this led to salinity problems in some crops as roots came into direct contact with fertilizer granules. Wilson found that using water-soluble fertilizer sources eliminated this problem.

The majority of exported alfalfa is grown in the western states. Exporters in these states have expressed concern that their overseas customers may not accept the presence of a genetically modified crop. Export consumer preference may also be highly dependent on price. At a minimum, buyers will need to initially differentiate transgenic hay from non-transgenic hay in their export lots. It is likely that the tools and management practices to achieve this will be in place prior to commercialization. For example, sensitive tests to detect the presence of the RR gene in hay and seed are currently being developed. Full approval by government agencies for animal feed and food in the United States and major export markets is currently being sought. The protein responsible for Roundup tolerance has already been approved for feed and food use in other crops in the primary export countries. Roundup Ready alfalfa will not be commercialized until regulatory and safety approval is obtained in the United States and Japan, according to Forage Genetics International and Monsanto. The Japan Feed Trade Association stated in July 2002 that it had no concerns about RR alfalfa, since biotechnology-enhanced canola, soybeans, corn, and cottonseed have been used successfully for feed in that country.Processing tomatoes are an important cash crop to annual agricultural systems in the Central Valley of California. California processing tomatoes have an annual farm gate value of $1.17 billion and are currently the 10th most valuable agricultural commodity produced in the state . In 2020, California produced 11.4 million tons of tomatoes across 230,000 acres, making up over 95% of US tomato production . California is also important on the international market, vertical grow rack system producing about 30% of the world’s processing tomatoes . The San Joaquin and Sacramento Valleys are the two major tomato growing regions in California, with five counties comprising the majority of the production acreage .

The California tomato industry is based on grower-processor contracts in which variety, amount, and often management are agreed upon before planting. Tomatoes typically are transplanted from March until July and harvested from July until October. Tomatoes are mostly planted in single or double plant lines on 60-inch, 66- inch, or 80-inch beds. The industry has widely adopted drip irrigation technology in recent decades, replacing furrow flood irrigation. Tomatoes are mechanically harvested when about 90% of the fruit are red and transported directly to processing facilities. With advances in genetics, management, and equipment, California processing tomato fields produce 50 tons of fruit per acre on average . The California tomato industry is highly specialized and utilizes many aspects of ‘custom farming’ in which a sub-contractor provides a specific service to the grower or processor. Tomatoes are mechanically transplanted, often by a third-party transplanting company or processor that may serve multiple growers and whose equipment may be used in many different fields each season. Tomato harvest follows a similar scheme, with harvesting companies or processors owning and operating harvest equipment, harvesting many fields across the state each year. California tomato growers must manage a variety of pests, including several weed species. Major weeds include black nightshade and hairy night shade , field bindweed , and small seeded broadleaves . Conventionally grown tomatoes utilize a combination of pre-emergence and post emergence herbicides along with cultivation and hand weeding for effective weed control. Before planting, a preplant incorporated herbicide is usually applied to the bed surface and incorporated with tillage equipment during final bed shaping. Common PPI or pre-emergence herbicides used in tomato include trifluralin , rimsulfuron , pendimethalin , S-metolochlor , and metribuzin . Later in the season, common post-emergence herbicides include clethodim , halosulfuron , metribuzin, rimsulfuron, sethoxydim , and carfentrazone . Integrated weed management control practices include crop rotation, use of transplants, drip irrigation, and cultivation . Broomrapes belong to the Orobanche and Phelipanche genera in the Orobanchaeceae family . Broomrapes are obligate parasites, lacking chlorophyll, thus gaining all of their nutrients from parasitized host plants .

Of the numerous broomrape species, seven are economically important to agricultural crops globally . These include crenate broomrape , nodding broomrape , sunflower broomrape , foetid broomrape , small broomrape , Egyptian broomrape , and branched broomrape . These broomrapes parasitize plants from the Apiaceae, Asteraceae, Brassicaceae, Fabaceae, and Solanaceae families including crops such as carrot, sunflower, rapeseed, faba bean, and tomato . Broomrapes cause economic damage to agricultural crops by reducing yield, with reproductive tissue disproportionately affected . In Chile, tomato growers report up to 80% crop loss in fields infested with branched broomrape , while growers in Sudan have reported total crop failure . Yield losses from broomrape infestations are thought to amount to $200 million annually in Turkey . Broomrape population density has increased in many near eastern and north African countries alongside production of broomrape-sensitive crops, threatening food supply in this region . Parasitic plants, including broomrapes, threaten the food security of communities around the globe, and research must be conducted to develop management strategies to reduce yield and economic losses . Branched broomrape is a parasitic plant native to the Mediterranean region of Eurasia. It is a holoparasite that parasitizes a host plant’s root system resulting in loss of vigor, yield reduction, and even death to the host . In the United States, there are four species of weedy broomrapes known to parasitize economically important agricultural crops: small broomrape, Louisiana broomrape , Egyptian broomrape, and branched broomrape . In the past several years, branched broomrape and Egyptian broomrape have been reported in California, including Yolo, Solano, and San Joaquin counties . In California, branched broomrape is “A” classified, being “an organism of known economic importance subject to California State enforced action involving eradication, quarantine regulation,containment, rejection, or other holding action,” while Egyptian broomrape is classified as a “Qlisted” noxious weed .

A field reported to be infested with an “A-listed” pest such as branched broomrape will be evaluated by the local county agriculture commissioner, quarantined, and that season’s crop destructed. For at least two years following this discovery, a hold order is placed on the field and only approved non-host rotational crops may be planted. Broomrape has been discovered in conventional, intensely managed fields, suggesting that conventional weed control practices and currently registered herbicides do not provide adequate broomrape control. Currently there are no proven management practices to selectively control branched broomrape in tomato, making this parasitic weed a serious threat to the California processing tomato industry. Branched broomrape was first discovered in California in 1903 in Butte County, followed by discoveries in Alameda, Colusa, Sacramento, San Benito, Santa Clara, San Joaquin, Ventura, and Yolo Counties . After a severe infestation was discovered in the Sacramento Valley in 1959, an intense industry wide eradication effort began at a cost of $1.5 million funded by a marketing order program . From 1973-1982, field scouting combined with fumigation with methyl bromide reduced broomrape seed banks and eradication was thought to have been successful . Branched broomrape is considered to be one of the most common and destructive broomrape species, infesting 2.6 million hectares of crops across Asia, North Africa, and the Mediterranean . Branched broomrape’s reemergence in California is extremely concerning to the viability of the California processing tomato industry for several reasons. California’s Mediterranean climate is similar to branched broomrape’s native range,agronomic practices make the proliferation and spread of broomrape’s minute seeds in and among fields highly likely, while broomrape’s phenological development make it inaccessible to conventional weed control practices and infestations difficult to detect. California’s regulatory environment make soil disinfetation via fumigation difficult and costly and there are no registered herbicides for broomrape control. Broomrape control strategies should focus on preattachment or very early during their lifecycles, when they are most vulnerable and before yield loss occurs . Broomrape’s unique phenology, specifically how it develops below the soil surface for 2/3 of its lifecycle, makes it unavailable to many conventional weed management techniques such as cultivation, post emergent herbicides, hand rogueing, etc. In addition, vertical farming racks rapid progression from emergence to flowering and relatively small stature make scouting for the parasite in tomato fields extremely difficult. Broomrape seeds are extremely small . Their small size results in limited seed carbohydrate reserve and broomrape species have evolved mechanisms to ensure successful host attachment. Broomrapes require several specific conditions for germination: a stratification period, sufficient soil moisture, and detection of specific root exudates .

Broomrape respond to a group of hormones known as strigolactones which include orobanchol, didehydroorobanchol, and solanacol . The detection of these exudates ensures the seed is within an acceptable distance to a host plant so that the broomrape radicle can intercept a host root and begin to form a haustorium. A haustorium is a modified rootstructure that connects parasitic plants to the host plant’s root vascular system, allowing the broomrape to become a sink for water and nutrients . After sufficient nutrients have accumulated, the broomrape will form a swollen nodule known as a tubercle to store nutrients and water . As the parasite matures, shoots will form from this tubercle, emerge above the soil surface, develop flowers that selfpollinate, and produce seed. Egyptian broomrape is the most limiting factor in tomato production in Israel and many neighboring countries accounting for 30% of total losses caused by all agronomic constraints and resulting in annual losses of up to $5 million . In Ethiopia, as of 2009, state sponsored farms had given up growing processing tomatoes in historically fertile regions because of broomrape infestations . In northern Israel, increasing infestations of broomrape over the last 30 years caused many growers to abandon tomato in lieu of less profitable non-host crops . Chile has historically faced challenges with broomrape in processing tomatoes , and the parasite has become increasingly widespread in that country. Researchers in Israel have developed a decision support system, named PICKIT, to manage Egyptian broomrape in processing tomatoes . The PICKIT system relies on a growing degree day based model to inform precise applications of targeted chemical applications. The PICKIT system has various herbicide programs related to different infestation levels and relies on pre-plant incorporated treatments , chemigation treatments , and foliar treatments. The PICKIT system utilizes two acetolactate synthase herbicides to control broomrape; a sulfonylurea applied preplant in conjuction with low dose applications of an imidazolinone. These herbicides include sulfosulfuron and imazapic . These applications are made according to the GDD model to target specific broomrape development stages, specifically when it is a nutrient sink on the tomato plant, resulting in rapid translocation of herbicide from the host to the parasite. In 2016, commercial tomato growers in Israel deployed the PICKIT system and achieved 95% Egyptian broomrape control in 33 fields . Israeli researchers have partnered with Chilean researchers to adapt the PICKIT system to Chilean processing tomato growing conditions. Chile, like California, has infestations of branched broomrape Branched broomrape has been found in several counties in California, including two of the top five producing counties . While currently an “A-list” quarantine pest requiring crop destruction, there is a high likelihood this pest will become widespread enough to require management programs like any other weed. The PICKIT system developed in Israel could provide similar management in California. However, because there are differences between the Israeli and California processing tomato systems and broomrape species , the PICKIT program must be evaluated and calibrated for use in California cropping systems. Imazapic is registered in the southern United States for use as an early post-emergence herbicide in peanuts but is not registered in California for use on any crops. Sulfosulfuron is registered in many states for use as a selective systemic herbicide on broadleaf weeds in wheat and is registered in California for non-crop use but not in tomato . In order for these herbicides to potentially be registered under an emergency use authorization for broomrape control or an indemnified label under California production conditions, there must be research on their performance and crop safety. The overall goal of this study was to determine if there was potential to adapt the PICKIT decision support system for branched broomrape control in California processing tomatoes and to provide herbicide registration support data needed to register PICKIT herbicides for special use in California. To evaluate the PICKIT system under California conditions, a series of crop safety and efficacy field experiments were conducted in 2019 and 2020.

Floodwaters are generally maintained at 10-20 cm for the entire season. California rice cultivars are temperate japonica inbred lines, with sufficient vigor to quickly elongate and escape deep floodwaters . Water seeding was adopted in the region in the 1920’s to suppress competitive grass weeds , and has remained the preferred method of rice cultivation in California, even as herbicides have been widely available for decades . Although the WS rice cropping system is optimized for the region, it is not without disadvantages. Water seeding encourages higher seeding rates that can incur higher production costs, because floating seedlings are subject to wind drift and predation, both of which may result in reduced or patchy stands at lower seeding rates. Surface-rooted rice is also prone to lodging. Irrigation water usage is also of concern , as California is regularly beset by drought and irregular rainy seasons exacerbated by climate change. The near-exclusive use of permanently-flooded rice culture has also resulted in a small spectrum of well-adapted and competitive grass species , as well as aquatic broad leaves and sedges . As the permanently-flooded cropping system essentially precludes cultural weed management practices such as cultivation, and as large farm size and high labor costs discourage hand-weeding, herbicides are the sole means of weed control outside of water management for most California growers . Although effective herbicides have been available for California rice since the 1960’s, the nearly exclusive use of water seeding has meant that the number of registered active ingredients remains low, amid pesticide contamination concerns and California’s stringent regulatory structure . This limited herbicide palette restricts herbicide rotation. Since rice is largely grown year after year in the region, vertical grow room design the combined effects of a water-seeded monoculture, and extensive use of limited available herbicides on a small weed spectrum, have resulted in widespread cases of herbicide resistance .

Cultural methods for weed and resistance management in California rice are generally limited to modifications of the dominant WS system . For example, with the “stale seedbed” method rice fields are prepared for planting as usual, but are flushed with water prior to seeding to promote weed germination . Nonselective herbicides are typically used as a burndown treatment on emerged weeds , and fields are then flooded and air-seeded as usual. This method can be a useful strategy to manage weeds that are resistant to registered rice herbicides, by introducing novel nonselective herbicides without known local resistance . However, implementing a stale seedbed can delay rice planting and shorten the growing season, potentially depressing yields . Stale-seedbed can be followed by drill seeding to shorten the delay between burndown treatment and rice planting. In DS systems, rice is dry-drilled to 1.25 – 2 cm, and fields are flush irrigated intermittently as the stand develops and herbicides are applied, then flooded for the remainder of the season 30-40 days after seeding . This method discourages aquatic weeds and algae , however in this system the rice often emerges synchronously with grass weeds , reducing the stand’s ability to compete with weeds. This also limits management of resistant weeds to the short preplant burndown window. However, if rice seed is sown to depths exceeding 2 cm, it might emerge later than early-germinating grasses , thus allowing cultural or chemical weed management practices to be used safely on emerged weeds without injuring the rice . This would lengthen the stale-seedbed burndown window, allowing more weeds to be managed by the burndown treatment. As California rice cultivars are bred for water seeding, they have suitable vigor to emerge through water depths of up to 20 cm . This high vigor may make California rice cultivars suitable for drill seeding to depths greater than 2 cm.

If planting vigorous rice deeply can permit delayed, but even rice stand emergence, it should be possible to combine drill seeding with a stale seedbed as an integrated approach to herbicide resistance management. This “stale-drill” method could permit the use of a novel mode of action in a post plant-burndown treatment, which would safely manage key herbicide resistant weeds prior to stand emergence, without crop injury or delayed planting. Studies under controlled conditions comparing several California rice cultivars’ responses to burial depth indicated varying levels of vigor between cultivars . The cultivar ‘M-209’ was found to have the greatest vigor of those tested, in terms of below-soil elongation, emergence, and early season development. The purpose of this study was to compare stand establishment and yield components of M-209 and the most commonly planted cultivar, ‘M-206’, when seeded at two different depths. In addition, herbicide programs featuring a PPB application were evaluated for optimized late-season weed control.Studies were conducted in a split-split-plot design, with planting depth as the main plots, cultivar as the subplots, and herbicide treatment as the sub-subplots, with three replicates each year . Main plots were 16 x 18 meters, and were surrounded by 2.2-meter wide levees to allow independent flush-irrigation and flooding. Planting depths in main plots were either 3 or 6 cm. Within the main plots, cultivars ‘M-206’ and ‘M-209’ were planted on approximately half of the plot area each, separated by a 1.5 m unplanted buffer strip. M-206 is the most commonly planted cultivar in California , grown on roughly half of the planted area, with a heading time of 86 days . M-209 is a newer, higher-vigor cultivar that with a heading time of about 92 days . Rice was dry-drilled at a rate of 121 kg ha-1, using a mechanical seed drill with 17.8 cm row spacing. Planting dates were 28 May 2018 and 19 June 2019 .Flush-irrigation for main plots was done by powered pumps. Main plots were flushed immediately after planting, and water was allowed to infiltrate the dry soil.

Subsequent flushes were applied to each main plot independently, as the soil dried and cracks appeared. After final herbicides treatments were applied, the entire field was flooded to 10 cm average water depth for the remainder of the season. Harvest dates for 2018 and 2019 were 20 October and 29 October, respectively.Herbicide programs were evaluated for PPB efficacy, and differences of control for later-emerging weeds. Sub-subplots of herbicide treatments were applied in 3 m x 6 m zones . Three herbicide treatments plus an untreated control were used . Herbicides were applied with a 6 m boom sprayer with six 8003XR flat-fan nozzles , CO2-pressurized and calibrated for 187 L ha-1 carrier volume. At the date of first observed rice emergence, treated plots received a post plant burndown application of glyphosate at 870 g a.e. ha-1 + 2 % w/v ammonium sulfate . Follow-up early-postemergence and mid-post emergence treatments were applied at 3- leaf and 4-leaf rice stages, respectively. EPOST treatments consisted of bispyribac at 37 g a.i. ha-1 + 0.4% v/v organosilicone surfactant , applied alone or with a tankmix partner of pendimethalin at 1070 g a.i. ha-1 or clomazone at550 g a.i. ha-1. MPOST treatments were cyhalofop + 2.5% v/v crop oil concentrate.The study site weed seedbank was previously described in Brim-DeForest et al. and BrimDeForest et al. . Weed control evaluations measured the early-season efficacy of PPB treatments in this program, clone rack as well as the contributions of PPB treatments to overall control. The potential for later applications of pre-emergent herbicides to enhance control of lateremerging weeds was also investigated. Weed responses to herbicides and treatment timing differences imposed by rice planting depth were measured. Weed density in each plot after PPB treatment was estimated 20 days after planting by counting plants in 30 cm x 30 cm quadrat samples, with three averaged subsamples per plot. Follow-up weed density counts were performed at 45 and 70 DAP, following the same methodology. Echinochloa spp. and sedges were grouped in their respective genera for quadrat counts.Rice growth and development in response to herbicide program and planting depth were measured throughout the season. Of particular interest were crop responses to PPB applications of glyphosate, as well as the effects of planting depth and weediness on crop development and yield components. Date of rice emergence was determined by visual estimation, and defined as >10%of rice plants visible at the soil surface, and was used to time PPB treatment.

Rice stand density was recorded at 21 days after planting by counting plants in 30 cm x 30 cm quadrats, with three subsamples averaged per plot. Due to different maturation rates of the cultivars used in this study, tiller density was recorded at 90 DAP and 110 DAP by counting tillers in 30 cm x 30 cm quadrats, with three samples per plot. Time to 50% heading was estimated visually, and plant heights were recorded with a meter-stick at 120 DAP. Prior to field harvest, ten panicles per plot were randomly selected, hand-harvested, and dried for three days at 50°C. Grain yield per panicle and 1000-grain weight were measured, and adjusted to 14% moisture content. Filled and total florets per panicle were measured, and percentage of unfilled florets was calculated. Whole plots were harvested and yields measured with a small-plot combine with a swath width of 2.3 m, and were adjusted to 14% moisture content.All data –with the exception of time-to-heading– were subjected to ANOVA and linear regression analyses using the agricolae and emmeans packages in R , and JMP® 14Pro , using planting depth, cultivar, and herbicide treatment as fixed effects, and replicates as random effects. Significant year-by-depth and year-by-treatment and interactions for all data were observed; therefore, data were re-analyzed separately by year, using the same fixed and random effects as described above. In both years, no differences were observed between rice planting depths, cultivars planted, or among applied herbicide treatments for weed count data, therefore data for planting depth, cultivar, and treated plots were pooled and re-analyzed as treatment versus UTC . Similarly, in both years, no differences were observed between herbicide treatments for rice stand and yield components, therefore treated-plot data were pooled and re-analyzed as treatment versus UTC . Pooled data met assumptions of homogeneity and normality of variance, and were untransformed for analysis.Rice became visible at the soil surface by 7 DAP in 2018, and 6 DAP in 2019, by which time grass and sedge seedlings were very dense in all plots. At date of emergence either year, M-209 had slightly greater emergence than M-206 at both planting depths. Likewise, rice planted to 3 cm was slightly taller than rice planted to 6 cm, regardless of cultivar. Nevertheless, at DOE there were no differences in emerged seedling heights between cultivars or planting depths either year, and stands in all plots were even. In both years, glyphosate PPB was applied at DOE. Rice firstleaf tips exposed to the PPB treatment died off within a few days, however plants developed normally and exhibited no stunting, chlorosis, or other injury symptoms . Comparing pooled herbicide treatments with UTC plots, rice stand reductions were observed by 21 DAP in 2018 . Averaged across planting depths and cultivars, rice plants m-2 were reduced by 46% in UTC plots in 2018 , and were eventually reduced to zero. In 2019, no stand reductions were observed in UTC at 21 DAP, however significant reductions in all other growth and yield components were observed in UTC plots. Rice stand development in treated plots was affected by cultivar and planting depth both years. In 2018 stand density for M-206 and M-209 planted at a 6 cm depth was reduced by 15.4% and 5.2% , respectively, relative to the 3 cm planting depth. However, stand density was not affected by cultivar or planting depth in 2019. Increased tillering in M-206 compensated for stand reductions in the 6 cm planting depth in 2018; M-206 tillering decreased only 3.2 % between the 3 cm and 6 cm planting depths. For either cultivar, tiller density decreased slightly at 6 cm planting depth in 2018, and increased slightly in 2019. Cultivar differences in tillers plant-1 were only observed in 2018, averaging 2.3 and 1.9 tillers for M-206 and M-209, respectively. Time to heading was affected by cultivar in 2018, and by both cultivar and planting depth in 2019 . Time to 50% heading in 2018 was 75 DAP and 83 DAP for M-206 and M-209, respectively. In 2019, T50 for M-206 was 76 DAP for both plating depths.

Stale-seedbed can be followed by drill seeding to shorten the delay between burndown treatment and rice planting. Drill seeding rice typically involves sowing seed to 1.25-2 cm and flush irrigating fields for the first few weeks as the rice stand develops and herbicides are applied, before flooding for the remainder of the season . This method discourages aquatic weeds and algae, but tends to favor grasses . Furthermore, as the crop is typically sown fairly shallowly, it emerges synchronously with competitive grasses reducing the stand’s ability to compete and further limiting available herbicides. However, if rice is drilled to depths greater than 2 cm, the stand should emerge later than the majority of grasses. This may allow novel weed management practices to be used without stand injury . We hypothesized that planting California rice cultivars below the zone of active weed germination and emergence would delay rice emergence, yet not result in reduced rice stand. This would allow us to combine drill seeding with a stale seedbed as an integrated approach to weed management. This “stale-drill” method would permit the use of a novel mode of action in a post plant-burndown treatment, which would safely manage weeds prior to stand emergence, without injury or delayed planting. CHAPTER ONE details field trials conducted in 2016-2017. We explored the feasibility of staledrill planting, by planting cv. M-206 to depths up to 5.1 cm and evaluating stand establishment and herbicide programs. Aquatic broadleaf weeds and algae were suppressed by water management, and were not present in either study year. We applied glyphosate at 870 g a.e. ha as a PPB treatment just prior to rice emergence, either alone or in conjunction with other herbicides. Treatment delays had mixed effects on weed control. Glyphosate PPB was more effective at controlling Echinochloa spp. in 2017, vertical farming supplies reducing density by 30%, 48%, and 73% at 1.3 cm, 2.5 cm, and 5.1 cm depths, respectively. The greatest overall weed control either year was found with glyphosate + pendimethalin followed by penoxsulam + cyhalofop with rice seeded to 1.3 cm depth.

Planting rice deeper than 1.3 cm delayed emergence by 3 to 4 days in both study years. We found that rice stand and yield components were more strongly affected by planting depth in 2017 than in 2016, possibly owing to cool weather immediately after seeding. Yields in 2017 were reduced in deeper plantings by up to 72%. CHAPTER TWO outlines research conducted in glasshouses, with the aim of elucidating relative vigor of four California rice cultivars. Two experiments were conducted to evaluate rice cultivars for traits that would facilitate the stale-drill cropping methodology. Cultivars M-105, M-205, ‘M- 206’, and M-209 were evaluated for differences in germination, elongation, emergence, and early season morphology. M-205 and M-209 were found to have greater rates of total below-soil elongation, and greater rates of mesocotyl and coleoptile elongation overall, across depths. M-205 and M-209 were also found to have higher rates of emergence across depths. Differences between cultivars in above ground growth parameters of emerged seedlings were only found for rice planted at 0 cm, 6.4 cm, and 7.6 cm planting depths. Based on observed below- and above-soil growth and development, M-205 and M-209 exhibited greater vigor overall, as well as high levels of emergence from depths greater than 2 cm. CHAPTER THREE describes research conducted in the field in 2018-2019. Rice cultivars M-206 and M-209 were drill seeded to 3 cm and 6 cm depths. A PPB application of glyphosate at 870 g a.e. ha-1 was applied 6-7 days after planting at rice emergence, which controlled >50% of grass and sedge weeds. Aquatic broadleaf weeds and algae were suppressed by water management, and were not present in either study year. Glyphosate PPB caused rice first-leaf dieback, but no other symptoms developed. Planting depth and cultivar did not affect date of emergence either year. Deeper seeding reduced M-206 and M-209 stands by 15.4% and 5.2%, respectively, in 2018, but not in 2019. Increased tillering compensated for stand reductions in 2018.

Panicle yield components were largely unaffected by planting depth in 2018, however florets panicle-1 and filled grains panicle-1 were slightly greater for both cultivars seeded at 6 cm, compared to 3 cm planting depth. In 2019, M-209 suffered reductions in florets panicle-1 and grain filling when planted to 6 cm depth. Grain yields were not affected by planting depth in either study year. M-206 and M-209 grain yields were 10.2 T ha-1 and 12.2 T ha-1 respectively, in 2018, and 9.4 T ha-1 and 9.1 T ha-1 respectively, in 2019. This body of research has identified high-vigor California rice cultivars that are suitable for planting to depths up to 6 cm. In doing so, we identified critical rice vigor traits that may aid breeders in selection for lines that can rapidly escape deep seeding. It also serves as a successful proof-of-concept for the stale-drill method as an alternative stand establishment method in mechanized rice production. Finally, it establishes that using stale-drill permits the safe use of a PPB treatment with a non-selective herbicide at stand emergence. Proper water management and scouting are essential to ensure that PPB treatments do not injure emerging rice to the extent that weak or reduced stands result. However, by way of permitting the use of novel herbicidal modes of action, this method may be a useful rotational strategy in fields with difficult-to-control weeds, including herbicide-resistant populations or weedy rice.The California rice [Oryza sativa L.] growing region comprises approximately 200 000 ha in the Sacramento Valley. The rice cropping system is almost exclusively water-seeded , wherein pre-germinated seed is sown by aircraft into flooded fields. Seeds sink to the soil surface and peg down roots, emerging from the water after several days. Floodwaters are generally kept to 10 to 20 cm depth for the entire season. Water seeding was widely adopted in the region in the 1920s as a means to suppress competitive grass weeds , and has been the predominant method of rice cultivation in California ever since . Continuous use of water seeding has resulted in a small spectrum of weed species that are well-adapted to the system, and are very competitive with rice .

Water seeding conditions encourage aquatic broadleaf weeds such as arrowheads , ducksalad [Heteranthera limosa Willd.], resdstems , and Monochoria spp., and the sedges rice field bulrush [Schoenoplectus mucronatus Palla], tall flats edge and small flower umbrella sedge . In addition, grass ecotypes that are able to escape flooding depths of up to 20 cm, such as barnyard grass [Echinochloa crus-galli P. Beauv.] , early watergrass [E. oryzoides Fritsch], late watergrass [E. oryzicola Vasinger] , and bearded sprangletop [Leptochloa fusca Kunth ssp. fascicularis N. Snow] have become an important weed management issue in California rice. As the permanently-flooded cropping system effectively precludes the use of most other cultural weed management practices, for most growers herbicides are the sole means of weed control outside of water management .Although effective herbicides have been available for California rice since the 1960’s, the nearly exclusive use of the water-seeded system has meant that the number of registered active ingredients remains small, amid water contamination concerns and California’s stringent regulatory structure . To date, there are 13 registered active ingredients for water seeded rice in California, weed rack across nine modes of action . Most MOAs have only one registered A.I. . This limited palette restricts herbicide rotation. Since California’s rice acreage is largely planted back to rice each year, the combined effects of water seeded monoculture, limited available herbicides, and extensive use of individual MOAs on a small weed spectrum has resulted in widespread cases of herbicide resistance in the region . Herbicide resistance has been a major biologic and economic issue in rice for decades . The lack of diversity of registered herbicide A.I.’s and modes of action means that once resistance to a particular MOA arises, it can spread rapidly within and among fields as there may be few alternative herbicides to control the resistant populations. For example, L. fusca populations resistant to clomazone have only three other effective herbicides available , and two of those three, cyhalofop and thiobencarb, are subject to long water-holding restrictions after application which may reduce their utility for some growers. Efforts to combat herbicide resistance in California are also hampered by the fact that rice herbicides are more costly in California than in much of the world. Therefore, many growers are burdened with potentially unsustainable herbicide costs in order to control resistant weeds in their fields. Most cultural methods for weed and resistance management in California are modifications of the dominant water seeded system . One such method used by some growers is a stale seedbed. In this method, rice seedbeds are prepared as usual and flushed with water to promote weed germination.

Non-selective herbicides are used as a burn down treatment , and afterward the fields are flooded and seeded as usual. This method can be a useful strategy to manage weeds that are resistant to current rice herbicides, as well as reducing weed seed banks. However, due to the time needed to reflood and seed fields afterwards, stale seedbed use can delay rice planting, shortening the growing season and potentially depressing yields . Another common rice cropping system in mechanized rice is drill seeding . Drill seeding rice typically involves drill seeding dry seed to 1.25-2 cm and flush-irrigating fields for the first few weeks as the rice stand develops and herbicides are applied, before flooding for the remainder of the season . This method discourages aquatic weeds and algae, but tends to favor grasses . Furthermore, as the seed is typically sown to fairly shallow depths, it emerges synchronously with competitive grasses . However, if rice is drilled to depths greater than 2 cm, the rice should emerge later than the majority of grasses and sedges. This may allow novel weed management practices to be used without causing injury to the emerging rice . Although older semidwarf rice cultivars tended to have lower emergence rates from deep plantings , higher vigor semidwarf cultivars have been produced in recent years . For example, California rice cultivars are bred for water-seeding, and thus have suitable vigor to emerge through water depths of up to 20 cm . This high vigor may make California rice varieties suitable for drill seeding to depths greater than 2 cm.If rice cultivars can emerge quickly and evenly from deeper plantings, it may be possible to combine a stale seedbed with drill seeding. This “stale-drill” method could permit the use of modes of herbicidal action not registered for use in water-seeded rice. This would allow growers to safely manage herbicide resistant weeds and reduce seed banks prior to rice stand emergence, without injuring rice, delaying planting, or shortening the season. If used in rotation with water seeding, stale-drill can also vary the weed spectrum year over year, reducing the tendency of a small number of species to dominate. In this way, the stale-drill method might be a useful tool for herbicide resistance management in mechanized rice production worldwide. The purpose of this study is to test the hypothesis that drilling rice below the zone of active weed germination will delay rice stand emergence sufficiently to allow a safe application of a non-selective post plant-burndown herbicide treatment.Echinochloa spp. were the dominant weeds present in both years, followed by Leptochloa fusca ssp. fascicularis and sedges. Cyperus difformis and C. eragrostis were the only sedges present in 2016; no sedges were present in 2017. No broadleaf species were present in either year. Treatment timing differences due to rice planting depth had mixed effects on weed control, however, overall weed control was greatest with treatment 5 either year, regardless of rice planting depth. In both years, UTC, T1, and T2 plots were very weedy at all planting depths. Weed population density varied between years. Echinochloa pressure was greater in 2017 than in 2016, with 2017 UTC plots roughly 3.75-fold weedier than 2016 UTC plots. Echinochloa plant density generally decreased with more comprehensive herbicide treatments in both years , although decreases were more consistent in 2016. In 2016 glyphosate alone reduced Echinochloa spp. density from UTC by 40%, 19%, and 6% in 1.3 cm, 2.5 cm, and 5.1 cm riceplanting depths, respectively, whereas glyphosate f.b. pendimethalin reduced Echinochloa spp. density by 72%, 36%, and 17% over the same depths.

It was hypothesized that, as the water treatment pH increased, there would be greater removal of herbicide from the soil in the rinsate. As pH of the solution increased, the equilibrium of the weak acid herbicide would be pushed towards the anionic herbicide form resulting in lower sorption to the soil and greater removal in the rinsate. However, the opposite trend occurred for two of the herbicides . As water treatment pH increased, the concentration of saflufenacil and penoxsulam decreased in the aqueous solution extracted from the soil. Saflufenacil removal in the rinsate was greatest at pH 5 with about 78% and lowest at pH 8 with about 64%. At pH 5, about 35% of the penoxsulam was removal from soil and this decreased to about 22% removal at pH 8 . Indaziflam was below the detection limit of the instrumentation in all rinsate samples, regardless of pH.The results of the EC water treatments show that, as EC increased, herbicide removal decreased slightly . The effect of ionic strength on ionizable pesticide adsorption to soil has been well documented12; the common trend is that as ionic strength increases, the pesticide adsorption also increases . These data support that trend as well. The greatest amount of saflufenacil and penoxsulam was removed from soil in the 0.5 dS m-1 water solution rinse; about 70% of saflufenacil was removed from soil and about 25% of penoxsulam was removed. Meanwhile, in the 1.5 dS m-1 and 3.5 dS m-1 solutions, approximately 65% of saflufenacil and 22% of penoxsulam was removed . Indaziflam was below the detection limit of the instrumentation in all rinsate samples regardless of ionic strength of the rinse solution.Indaziflam was below the detection limit in all samples; however, it is not clear if this is due to strong sorption to soil or to degradation processes.

While indaziflam is considered moderately mobile to mobile in soil14, vertical farming racks it does have a higher Koc range than saflufenacil or penoxsulam23 meaning indaziflam would be more strongly sorbed to soil than the other herbicides in this study. Indaziflam has been reported to undergo photolysis in aqueous solutions rather quickly 14; samples were stored in the dark for much of the duration of the experiment. A brief follow-up experiment confirmed the laboratory lights did not cause photolysis of the chemical in aqueous solution under the conditions of the experiments . Saflufenacil dissipates relatively quickly in the environment23. The herbicide has biotic and abiotic degradation pathways but the most relevant pathway to this study would be hydrolysis in alkaline water13. The data set shows a significant decrease in herbicide removal from soil from pH 5 to pH 6 and 8 . The pH 7 data point was not statistically different from the other pH water treatments. There have been differing reports on penoxsulam hydrolysis. The Environmental Protection Agency states that penoxsulam is stable under hydrolysis conditions15 while Jabusch and Tjeerdema report triazolopyrimidine sulfonamide herbicides do undergo hydrolysis and the rate is dependent on pH24. There have been studies completed on two other herbicides in the TSA class which support pH dependent hydrolysis rates25-26. Given that the experimental samples were held at field capacity for seven days in this study, pH dependent hydrolysis could explain why penoxsulam concentrations were decreasing from 34% removal from soil at pH 5 to 22% removal at pH 8 .Adsorption mechanisms of pesticides are difficult to define because of the complex interactions between the soil surface, soil solution, and pesticide. Additionally, it is likely more than one adsorption mechanism occurs.

There are several mechanisms by which weak acid pesticide adsorption could be positively influenced by ionic strength – cations could displace hydrogen atoms from the soil surface resulting in a slight pH decrease that would favor a neutral pesticide form, more cations could be available to bridge the anionic form of the pesticide to the negatively charged soil surface, or cations could bond with the anionic pesticide resulting in a neutral form. A recent study on the adsorption-desorption properties of penoxsulam narrowed down the possible sorption mechanisms to H-bonding, cation bridging, and surface complexation with transition metals. The data set presented here supports the cation bridging mechanism. As ionic strength of the water treatment was increased, cation concentration increased resulting in the greater likelihood to bridge the anionic form of penoxsulam to the negatively charged soil surface. Figure 1.3 shows no statistical significance between ECw 1.5 dS m-1 and ECw 3.5 dS m-1 , this likely indicates most of the available binding sites of the soil were occupied close to ECw value 1.5 dS m-1 . Due to the similarity in size and ionizable functional group to penoxsulam, it is likely that saflufenacil is undergoing the same phenomena. The water treatments representing different irrigation water quality parameters did have a slight effect on saflufenacil and penoxsulam sorption to soil. The pH treatments indicated that both herbicides likely experience pH-dependent hydrolysis; saflufenacil and penoxsulam showed a decreasing trend in herbicide removal with increasing pH, the opposite of what the hypothesized pH effect would be. This indicates that even if irrigation water has relatively high pH, it is unlikely to substantially change the availability or movement of saflufenacil orpenoxsulam in California orchard soils. Results from the ECw treatments showed that flushing soil with a solution with moderate ionic strength could help saflufenacil and penoxsulam bind to soil versus low ionic strength. While there were statistically significant differences between water treatments, the overall effect on herbicide dissipation was minimal; the observed difference between the highest and lowest ECw treatment was only about 10% for each herbicide.

In the United States almonds are a $6 billion commodity grown solely in California making almonds the second highest grossing commodity in the state behind only dairy products . As of 2020 there were more than 500,000 bearing hectares of almond trees planted in California which produced 1.3 billion kilograms of almonds . Almonds are harvested by mechanically shaking the trees, sweeping the almonds into windrows, and picking the nuts up from the orchard floor. Preharvest herbicide programs and mowing are used to control vegetation that would otherwise reduce harvest efficiency . Glyphosate has been registered in almonds since the early 1990s and glufosinate has been registered since the early 2000s ; these are commonly used herbicides for preharvest orchard preparations because of their broad spectrum weed control and relatively short preharvest interval , three and 14 days, respectively. In 2018, over one million kilograms of glyphosate and nearly 300,000 kilograms of glufosinate-ammonium were applied in almond orchards . Because of the harvesting process, there is ample opportunity for the almond hulls, shells, and kernels to be in close contact with herbicide-treated soil. The majority of California’s almond crop, about two-thirds, is exported and generated more than $4.9 billion in 2019 . Of the exports, 22% were shipped in shell and 78% were shipped shelled . Asia is the largest aggregate market for in shell almonds while the majority of shelled almond shipments go to European markets . Exported shipments of almonds are subject to pesticide residue testing and must be at or below a maximum concentration set by the region’s food safety authority.The maximum residue limit for glyphosate and glufosinate in almonds differ by definition as well as concentration between the European Union and the US. In the United States, both glyphosate and glufosinate MRLs, which are commonly called tolerances, are defined to include the parent compound as well as its primary metabolites . For clarity these MRLs will be referred to as “total glyphosate” or “total glufosinate” if the concentrations of the metabolites are to be summed with the concentration of the parent compound. The US MRL for glyphosate in almond hulls is 25 mg kg-1 and 1 mg kg-1 for kernels. There is not a separate US MRL for in shell almonds because the residue in inshell almonds is determined by shelling the almonds and measuring the residue in only the kernels. The US MRL for total glufosinate in almond hulls and kernels is 0.5 mg kg-1 . In the European Union, the MRL for glyphosate is 0.1 mg kg-1 in almond kernels . The EU MRL for glufosinate includes its metabolites; the MRL for total glufosinate is 0.1 mg kg-1 . Glyphosate is registered in the EU until 2022 . A recent review completed by the European Food Safety Authority recommended that the MRL for glyphosate be reduced to 0.05 mg kg-1 and an optional total glyphosate MRL for the summation of glyphosate and its primary metabolites, AMPA and N-acetyl-glyphosate, set to 0.2 mg kg-1 . Hence, it is anticipated that in upcoming years glyphosate MRLs will be reduced, vertical grow rack and it is a possibility that the chemical may not be re-registered. According to statute, if at any time thesafety of a current MRL is reconsidered, the MRL can be reduced to the lowest limit of analytical detection which is 0.01 mg kg-1 .

Because of the importance of the European markets to the California almond industry and the importance of glyphosate and glufosinate to preharvest preparations, lab and field studies were conducted to evaluate the herbicide transfer from soil to almonds during harvest. The objectives were to determine if glyphosate and glufosinate residues can transfer to almonds from soil particles or directly sprayed almonds, whether increasing the PHI could substantially reduce the risk of herbicide in or on almond fractions and quantify the concentration of soil-bound herbicide in almond samples.This experiment was conducted to determine glyphosate transfer from directly-treated almonds to non-treated almonds. This was intended to mimic a situation where a small number of almonds fall to the ground very early and could conceivably be directly sprayed with preharvest treatments and then contaminate the later-harvested crop during harvest and handling steps. Two almonds were directly treated with 0.8325 MBq [14C]-glyphosate by using a microsyringe to dot the stock solution over the entire almond including the inside of the split hull and exposed shell. The two treated almonds were tumbled with nine non-treated almonds using the apparatus and methods described earlier. The almonds were tumbled using a rock tumbler for 15 minutes and let rest for 15 minutes. Before analysis the treated almonds were removed from the bottle, and the untreated almonds were dissected and analyzed for [14C]- glyphosate. This experiment was replicated four times.The whole almonds from each replicate from both soil transfer experiments and the almond-to-almond transfer experiment were separated for three different analyses: whole almond rinse, herbicide adsorption to almond fractions, and a surface swipe after a post-harvest mimicking process. All samples were analyzed using a liquid scintillation counter . The data were corrected for the background levels of radiation in the scintillation counter. The rinsate of whole almonds was used to determine how much [14C]-herbicide was loosely associated with the surface of the almonds. Three whole almonds were rinsed with water using gentle inverted shaking. The rinsate was collected into glass scintillation vials and evaporated using a vacuum evaporation system at 30°C . Once the samples were evaporated to near dryness, 10 mL of Ultima Gold™ was added to each vial. The samples were analyzed using the liquid scintillation counter. To determine how much herbicide was adsorbed to the almond fractions, three almonds were dissected into their hull, shell, and kernel components. Each component was homogenized using a mortar and pestle and liquid nitrogen. Approximately 500 mg of each homogenized almond fraction was collected into a combustion cone and combusted using a sample oxidizer . The combustion product, [14CO2], was collected in 20 mL of scintillation cocktail composed of 10 mL CarboSorb E® and 10 mL Permafluor® . Glass scintillation vials containing the [14C]-samples were analyzed using the liquid scintillation counter. The remaining three almonds went towards a post-harvest mimicking process. The almond hulls were discarded, and the shells were opened by hand cracking through a plastic barrier then discarded. The plastic was swiped using a filter paper and the swipe was added to a glass scintillation vial with 10 mL Ultima Gold™. The swipes were analyzed using the scintillation counter. The kernels were collected, homogenized and combusted, and the combustion product was mixed with scintillant and analyzed using the scintillation counter as described above.

This one application will provide 4 to 6 years of adequate sulfur nutrition to the new pasture plants. Visible symptoms of sulfur deficiency include stunting and yellow color, although these symptoms also commonly indicate nitrogen deficiency. If you suspect sulfur deficiency after pasture establishment, cut the top 4 to 6 inches off of leaves at early bloom and submit a plant tissue sample to a lab for analysis. If grass tissue results indicate a sulfur level of less than 0.10 to 0.15 percent, you may have a sulfur deficiency. Common solutions are broadcast applications of soluble sulfur fertilizers such as ammonium sulfate or gypsum.The overriding characteristic common to newly established, dryland plant species is their low seedling vigor and slow growth and maturation. Typically, dryland perennial seedlings are so slow to get started that even several months after seedling their slim, vertical stalks are difficult to see. Since perennial seedlings mature slowly and are particularly susceptible to stress, a grower may not consider the stand to be “established” until it is 3 years old. Potential causes of pasture damage or loss may include lack of moisture and consumption by any number of animals, including cattle, deer, rabbits, ground squirrels, mice, and insects such as grasshoppers. Proper timing of cultural practices, seedling methods, and weed control help improve soil moisture conditions, but grazing must be light and controlled during pasture establishment to avoid excessive seedling losses. Try not to allow grazing in the year of establishment, indoor weed growing accessories at least until the seedlings have completed their growth for the first growing season. Timingwill vary depending on elevation and site conditions, but this usually means no grazing before July 1.

Under favorable growing conditions, the seeded plants will have developed numerous leaves and produced a seed head. After the plants produce a seedhead and go dormant , livestock can graze them down to 3 to 4 inches in height. If growing conditions are poor and the plants do not produce a seedhead, do not allow grazing at all. Regardless of growing conditions, many people merely plan not to graze a newly established pasture in its first year, just to be on the safe side. Proper grazing management is hard to determine during that first year. Often, the greatest benefit to the pasture from grazing is that grazing animals remove weeds such as annual mustards and grasses. Consider any grazing during the first year to be a prescribed clean-up operation rather than an extensive feeding on perennial seedlings. The key is to avoid grazing either too early in the summer, too close to the ground, or in muddy conditions. Grazing in late fall or winter should be avoided if muddy conditions exist, since the pasture will have developed very little sod by then to stabilize the soil and prevent soil compaction or erosion. Although livestock grazing can be controlled during seedling establishment, it is often impossible to control grazing by wildlife. Small plantings usually are the most susceptible to wildlife damage since it only takes a few animals to completely defoliate a small stand. In areas with large numbers of deer, rabbits, ground squirrels, or elk, you can seed areas of five or more acres at a time to reduce the chance of a complete loss of stand from wildlife grazing, although some areas of your planting may still be severely damaged. Along with wildlife, insects such as grasshoppers, Mormon crickets, and black grass bugs can cause significant damage to new seedlings. During a year with high insect populations, you may have to apply some sort of control. In most cases, insecticides provide the best control for insects feeding on new seedlings, since a large insect population can destroy a stand in a matter of a few days.

You will have to choose the most appropriate insecticide to use based on the particular insect pest and local site conditions, so you will do best to consult an agricultural specialist in the area before you apply a treatment. The second season after seedling, your management efforts should still focus on pasture stand establishment and you should continue to follow similar grazing guidelines to those you used the first year. Try to delay grazing until the plants have had the opportunity to complete their full growth for the season. Once drought conditions and cool temperatures have forced the plants into dormancy, graze them to a height of 3 to 4 inches and avoid grazing in muddy conditions.If growing conditions are favorable during the first two years, plants generally are well established by the third spring and you can proceed to manage the field as an established perennial grass pasture. If the first two years are marked by drought conditions, allow a third year of restricted grazing. This timeline is most applicable to introduced species such as crested or intermediate wheat grasses that have good seedling vigor and grazing tolerance. Native species that grow slowly and are sensitive to grazing may need three to five years to become completely established.Be cautious and conservative when you manage livestock grazing on dryland pasture, since desirable, dryland plants are quick to be degraded and slow to recover. Do not start a problem that may persist for years, just in order to get a little extra grazing in one year. Be especially careful when you graze livestock during drought cycles that persist beyond a single growing season. The combined stress of drought and heavy grazing will significantly diminish plant vigor. Under severe conditions, improper grazing can lead to the loss of desired plant species, which will then be replaced by weeds. Weeds make pasture rejuvenation difficult and often lead to permanent changes in vegetation. Historical practice indicates that the best approach is to vary the season of use and to leave half of the forage growth ungrazed. For example, forage used in the spring this year should be grazed later in the growing season next year.

When grazing in late spring and early summer, leaving half of the current year’s growth is a conservative practice that preserves the plants’ energy reserves in their roots and stems. If grazing is delayed until late summer or fall, pastures can be grazed down to a 3- to 4-inch stubble height without causing harm. In practice, these recommendations are best suited to producers who have enough pastures to permit a rotation that grazes some fields early one year and late the next year.But if you only have a single pasture to work with, it is best to defer grazing until early summer in order to prevent weed invasion and allow the plants to recover their energy reserves. If the area receives ample precipitation, a single-unit pasture can occasionally be grazed in early spring, but always make sure to leave half of the current year’s growth and stop the grazing before soil moisture is depleted. When wheat grass pastures are grazed in early summer, it may be possible to graze them again lightly in the fall or early winter. If you do allow fall or early winter grazing, begin after the onset of winter dormancy and stop before the initiation of spring growth . Depending on what type of livestock are grazing, you may need to supplement their feed with hay in order to provide adequate nutrition during fall and winter grazing periods. Early spring grazing usually is not appropriate for degraded ranges or areas that are susceptible to invasion by annual weeds. In field trials conducted on Siskiyou County pastures that had high annual weed pressure, early spring grazing resulted in a more extensive invasion of undesirable annuals than in pastures subjected to late spring or summer grazing . This research suggest that canopy removal in early spring allows greater exposure to sunlight and seed-to-soil contact to encourage the establishment of annual weeds that out-compete later maturing perennials. For this reason, it is probably best to avoid early spring grazing.Even if you do not graze your pastures, vertical grow rack system you sometimes have to remove plant cover using non-grazing management practices to prevent insect and disease problems and fire hazard concerns. The decision whether to mow or burn depends on how you want the pasture to look as well as several site characteristics. If unmanaged, perennial grasses create large amounts of dry, dead grass , posing a fire hazard. You can leave some plant material intact to help prevent invasion by non-native annuals and weeds, but if you leave too much it can lead to insect and fire problems. When practical, try to mow and bale excess forage and so reduce the accumulation of thatch and accelerate its decomposition. The best time to mow is after perennial grasses produce seed. You may also want to use controlled burning to remove accumulated thatch. Burning is a risky endeavor, though, and must be coordinated with the local fire department or the California Department of Forestry and Fire Protection . The best time to burn is after completion of perennial grass growth, but the exact timing of the burn depends on permit restrictions as well as site characteristics and other vegetation growing on the site. The influence of soil properties on herbicide efficacy has been widely studied as well as the influence of spray water quality on herbicide performance. However, limited studies on the effects of irrigation water quality on herbicide dissipation have been completed. This study was conducted to evaluate the effects of water pH and salinity on the dissipation of saflufenacil, indaziflam, and penoxsulam in two representative California orchard soils.The experimental protocol is a modified version of the method published by Sheppard et al.. The experiment was a completely randomized design with each herbicide being tested in both soil types at every water treatment and replicated three times. The amount of soil used in this experiment was determined by the bulk density of the soil and the assumption of a 25 cm2 spray area and a 2 mm soil depth. Each loam experimental unit contained 5.4 g of soil and each sand replicate contained 6.1 g of soil. Soil was first treated with herbicide by weighing appropriate amounts of each soil into a weigh boat, pipetting 1 mL of herbicide solution onto the soil, homogenizing by vigorousmixing, then letting the mixture sit for 24 hours until completely dry. The treated soil was then transferred into a 50 mL centrifuge tube equipped with a 0.22 µm Nylon filter . Soil was brought to field capacity by adding 1.220 mL of water treatment to loam soil or 0.780 mL of water treatment to sand soil, covered with parafilm, and left in the dark, at room temperature for seven days. After the resting period, the parafilm was removed and the samples were centrifuged at 6000 m s-1 for 15 minutes using a Sorvall Legend XTR centrifuge . After the initial centrifugation, an additional 1 mL of the respective water treatment was added to each sample then samples were centrifuged again at 6000 m s-1 for 15 minutes. This process was repeated once more for a total of two 1 mL water treatment aliquots washed over every sample after the field capacity water was removed. A separate pilot study completed to establish the number of water treatment washes needed to remove the unbound herbicide from the sample indicated that two 1 mL washes was adequate for the purpose of the experiment . The centrifuge filter was removed and discarded while all water from initial incubation plus the two 1 mL aliquots were collected from the centrifuge tube and filtered using a 0.22 µm Nylon syringe filter. The filtered solution was collected in an HPLC vial and analyzed using high performance liquid chromatography .Analyses were performed with an Agilent C-18 Poroshell 120 column in an HPLC system equipped with a diode array detector. Mobile phase A consisted of ultrapure water and mobile phase B consisted of acetonitrile with 0.1% formic acid. Chromatography was accomplished using an isocratic elution of 60% mobile phase A and 40% mobile phase B. The method run time was 9 minutes. All samples were observed at 270, 268, and 205 nm which corresponded to the absorbance of saflufenacil, indaziflam, and penoxsulam, respectively. The approximate retention time of saflufenacil, indaziflam, and penoxsulam were 4.9, 2.5, and 2.6 minutes, respectively . Samples were background corrected and converted into units of percent removal from soil using 5-point calibration curves .

Expansion of intermodal and inland port capabilities can significantly lower transportation costs for commodity import and export flows, helping to make global markets more cost competitive, accelerating regional economic development, and attracting business. By extending the gates of container ports inland, inland port systems enable shippers to efficiently serve new logistics pathways supporting online business divisions and e-commerce. Being able to serve customers with next-day, same-day, or even one-hour parcel deliveries is highly valuable to businesses, and many have reorganized their supply chains into multichannel configurations by replacing regional distribution centers with smaller, forward distribution centers in urban areas. Many of these warehouses need to be replenished with multiple incoming truckloads each day, in addition to generating many outgoing trips for local deliveries. Such fulfillment centers are increasingly co-located with manufacturing centers and intermodal ports, leading to more numerous and larger freight clusters around intermodal rail heads. Three commodities, “mixed freight,” “plastics and rubber,” and “other foodstuffs,” appear in the top ten commodities in Georgia for both ton-miles and value. Mixed freight is a commodity group suggesting the cargo consists of a variety of different types of products. It is the most common commodity arriving at distribution centers as well as many retail businesses and restaurants because the commodity can include certain food items, hardware, office supplies, clothing, and much more. Because distribution centers often handle a variety of goods to serve their customers, the generalized nature of the mixed freight commodity make it a useful classification and reduce administrative burden, compared with using multiple specific product classifications. While not all mixed freight movements can be unequivocally associated with distribution centers, vertical cannabis freight flows for the commodity are more likely to be observed along intermodal freight systems in drayage movements between intermodal terminals and fulfillment centers, and beyond in delivery movements to customers and points of sale.

Because of its expected on-road behavior, the commodity is more likely to be one that could technically achieve high penetration of BE truck technology.The frequent proximity of forward distribution centers, intermodal ports, and population centers improve electrification prospects for vehicles on freight vocations connecting these locations by shortening typical trip distances and encouraging a “out-and-back” tour cycle, where trucks begin and end their routes at the same location, making charging equipment siting more straightforward. It is hypothesized that trips to and from intermodal ports could have a relatively high number of operational characteristics that make these flows high value opportunities for investment in BE deployments, especially as intermodal flows continue to grow. High utilization and miles traveled typically improve the economics of BEVs. Increasing trip frequencies could represent increasing electrification benefits, so long as BE technology can adequately fulfill service demands within the constraints of battery capacity and charging requirements. Exploring these parametric relationships and testing these hypotheses was central in the design of the use-case study.Container drayage is typically conducted using Class 8 combination tractor trailer day cab units. For this use-case, we assume that the fleet is a small privately owned and operated third-party logistics operation consisting of three MY 2008 Class 8 combination trucks, all performing similar drive cycles on the same route. The trucks are assumed to travel from ARP to the distribution center with a full 20-foot shipping container of payload. Upon arrival, the full container is unloaded on-chassis at a staging area or delivery bay. The truck then picks up an empty container chassis and returns to ARP. The total distance of the tour on public roads is 122.2 miles. The vehicles have been operating on this vocation since their acquisition.

The owner-operator is planning to evolve their fleet and is seeking to understand how the energy use and economic implications of fleet management decisions will affect their business. They have decided to replace their vehicles with new MY 2023 trucks and want to understand electrification potential for their operation. To quantify the pros and cons of fleet electrification compared to the purchase of new traditional diesel trucks, we analyze both onroad and upstream energy consumption and emissions for each technology and fuel type for this use-case. We also quantify fuel, maintenance, and capital costs of both purchasing scenarios. MOVES is the federal regulatory model for quantifying on-road emissions and energy consumption for any use-case. MOVES essentially calculates the second-by-second power demand for a vehicle in units of vehicle specific power , or in the case of heavy-duty vehicles, scaled tractive power .For this analysis, road grade impacts on energy consumption are not considered. This area of northern Georgia does possess considerable elevation changes and the presence of grade on truck routes could significantly improve or hinder electrification process. Route segments with high percentages of downgrade are opportunities for energy savings and charge regeneration via regenerative braking systems. Routes with steep upslopes increase energy demand on the driving cycle. Given that downgrades never recover all of the energy lost moving uphill, routes with significant grace can limit the feasibility of some routes for BE MHDV applications. Grade effects impact outcomes on a case-by-case basis and warrant inclusion in subsequent studies but are out of scope here. In the TCOST tool, which will be discussed in the next section, energy demand effects of road grade are captured by the fuel consumption user input which informs the model’s energy use assumptions.

To calculate VSP for every second of the vehicle’s driving cycle, a driving cycle with 1-hz speed and acceleration data is required. To capture the energy consumption effects of evolving driver behavior across different road types on this tour, a composite driving cycle was created using various standard regulatory cycles for heavy duty trucks with some modifications. In this manner, the generated driving cycle was crafted to be as realistic as possible until telematic device deployment can provide second-by-second data. The driving cycle is one-way between ARP and the distribution center. Its profile is depicted in Figure 6, which is color-coded to show how each segment of the trip was combined. The composite driving cycle was manufactured using various heavy heavy-duty truck cycles made available by Georgia Tech through the U.S. EPA and state regulatory agencies. The beginning of Segment 5, which is the leg of the trip on GA 140 between the I-75 exit ramp and the distribution center access road , is a modified version of a U.S. EPA HHD truck creep cycle used for characterization for truck emissions in California. The total travel time for this one-way driving cycle is 104.3 minutes. For simplification, we assumed a truck on this use-case would execute this driving cycle with a full container load before executing it again in reverse with an empty container as the return trip.Energy consumption for the driving cycle was 461.58 kWh for the MY 2023 truck in 2022. Assuming a ten metric ton payload, this equates to 1.324 ton-miles per kWh for the MY 2023 truck. Fuel consumption was 11.34 gallons. BEVs have higher curb weights than vehicles with traditional power trains because of the added weight of their battery packs. For weight-constrained shipments, studies have found electrification of freight trucks will require a maximum payload reduction anywhere from 1.25 to 2.0 or more tons to accommodate the increased weight of the electric power train.Reducing the tonnage of cargo per truckload can negatively affect profit margins and potentially disrupt supply chains and the effects of electrification on the ton-mile capabilities of a fleet must be considered for comprehensive analysis. In this example, we assume the payload is constrained by volume rather than tonnage such that an increased curb weight will not necessitate a decreased payload and should not have any effect on the quantity of goods delivered. More refined analyses can be performed if actual payload data can be collected for individual use cases. Electrification of this use-case is technically achievable. Many new electric Class 8 combination tractors on the market have battery capacities of 500 kWh or more. However, grow racks nameplate capacity is not representative of available charge, as BEV systems will typically prevent batteries from depleting below a certain threshold of total capacity to preserve battery health and longevity. Assuming a 550-kWh battery, the driving cycle could be completed so long as at least 84% of capacity was actually available.

The primary implementation challenge is operational. Designing charging schedules that are symbiotic with delivery schedules and do not cause unacceptable amounts of downtime is critical to the success of BE technology on this vocation. To be able to transition to BE trucks entirely, the vehicles would need to have an opportunity to charge after each one-way trip on the route, which might necessitate the acquisition of multiple chargers and garage locations near each terminus. To evaluate the financial aspect of BE truck purchases as compared to traditional ICE truck purchases, a series of assumptions guided by real-world conditions observed today and projected into the future were constructed. Purchase prices for Class 8 BE MHDVs were collected from PG&E’s vehicle catalogue. Diesel truck purchase prices were collected from OEM specification sheets and websites, as well as from California HVIP. For this use-case example, a new MY 2023 Class 8 diesel truck was estimated to cost $107,433 and a comparable BE option was estimated to cost $300,000. In Georgia, new vehicle purchases are subject to a 6.6% title ad-valorem tax . Additionally, all new Class 8 vehicles are subject to a 12% federal excise tax at the time of purchase. Diesel and electricity price projections were collected from EIA and are shown in Figure 9 and Figure 10. Maintenance costs per mile were gathered from AFLEET and California HVIP. All financial assumptions are displayed in Table 6.Using the parameter values in Table 6, the total cost of ownership of purchasing new BE trucks is compared to that of new diesel trucks. It was assumed the fleet manager would opt to pay a 10% down payment at the point of sale for the new vehicles and that they would finance the capital cost of the vehicles over a 72-month period at a 5% interest rate. Based on the composite driving cycle constructed for this use case, we assumed that a typical day’s operation would be about 140 miles round trip for 250 workdays per year, and that the average fuel economy was 5.38 miles per gallon. The new vehicles were assumed to have a 20- year lifespan, and retired vehicles were assumed to have no real resale or salvage value. With these assumptions, the total cost of ownership was modeled, including purchase price and financing, operation cost, and maintenance cost. All future cash flows were discounted using a 5% discount rate. BE powertrains are more efficient than ICE powertrains. CARB has found that heavy duty electric trucks have energy efficiency ratios ranging from 3.5 to more than 7 when compared to diesel trucks, depending on operational speed. The efficiency ratio curve produced by CARB is reproduced in Figure 11. The average speed on the composite driving cycle is 32.8 mph. By using the regression equation provided by CARB, the average speed equates to an efficiency ratio of 3.73. Based on the ICE efficiency calculated at 5.38 mpg, the BE efficiency is found to be 20.05 mpge, or 0.52 miles per kWh.Electrifying this use-case would save the fleet $3,732.41 per vehicle, if operations could be designed to accommodate the technology. This includes the cost of two Level 2 charging systems, which could in theory be deployed near either end point of the route to allow for charging as needed after each one-way trip. Of course, other real-world considerations, like acquiring property for a second depot to install the charger on, may also increase costs for the BE truck pathway. Overall, the break even point for the BE truck would not be until its 20th year of operation. Performing more than one round trip per day, leading to a greater number of miles travelled, would improve the economics of electrification on this route because the bulk of the savings are in per-mile operating cost and maintenance cost. If charging schedules can be designed to accommodate delivery needs, and the demand for deliveries is adequate,increasing the freight activity in this freight operation would make electrification much more attractive. Finally, BEVs do not have tailpipe emissions.