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 .