California Agriculture

We conducted a 5-year study on the impact of grazing on stream-channel bare ground and erosion, and a 3-year study of cattle-trail erosion on intermittent stream channels draining grazed oak-woodland watersheds. While the concentration of cattle along stream banks during the dry season resulted in a significant increase in bare ground, we were unable to detect stream-bank erosion resulting from any of the grazing treatments applied. However, we did find that cattle trails are an important mode of sediment transport into stream channels. While cattle trails are common on grazed rangeland, excessive trailing often indicates that stock watering points are too far apart.

Spring-fed wetlands perform many important functions within oak-woodland landscapes, and livestock grazing modifies these functions. We used 10-year (long-term) and 3-year (paired-plot) experiments to better understand grazing management effects. We studied spring ecosystem responses in plant composition, diversity and cover; channel morphology; water quality; aquatic insects; and greenhouse gases. Lightly and moderately grazed wetlands exhibited lower insect family richness than ungrazed springs. Plant cover was maintained for the first 7 years of grazing, and plant diversity was not significantly affected. At the same time, removal of grazing decreased emissions of the greenhouse gas methane, and increased nitrate levels in spring waters. The results reveal important management tradeoffs relative to key response variables. In general, light cattle grazing at springs appears to be desirable from an ecosystem function perspective.

We examined the efficacy of using transparency-tube measurements to estimate turbidity, total suspended solids (TSS) and particulate nitrogen and phosphorus concentrations in several California waterways. Just as lowering a black-and-white disk (Secchi disk) into a lake provides a convenient way to measure its water clarity, a transparency tube offers a practical alternative for measuring water clarity and suspended solids concentrations in California streams and waterways. While transparency relationships with turbidity and TSS are strongest within a given sampling location, these relationships are relatively robust across a wide range of water bodies displaying contrasting conditions. However, transparency-tube measurements appear to have limited value in predicting particulate nutrient concentrations, even at a given sampling site. The low cost, ease of use and excellent repeatability of measurement make the transparency tube a potentially valuable tool for anyone interested in monitoring water quality, including farmers, ranchers, citizen volunteer groups, schools and local governments seeking to get involved in watershed monitoring programs.

The herbicide clopyralid (Transline) is commonly applied by air to control yellow starthistle, a noxious weed, in California. In laboratory studies, clopyralid toxicity in Fowler’s toad was low, indicating a wide safety margin when used under field conditions. In addition, monitoring of clopyralid drift following aerial application demonstrated that 98-foot (30-meter) buffers between treatment areas and water sources provided adequate drift protection for an adjacent stream and vernal pools. Nevertheless, to ensure that movement of the herbicide to water sources is minimized, it is important to prevent application error, particularly accidental encroachment into established buffer zones. This study demonstrated that drift potential for clopyralid was minimal even with an aerial application and a slight downwind breeze toward sensitive aquatic sites. It is also the first report demonstrating a high tolerance to clopyralid in larval toads.

Many of the dairies in California’s Central Valley use a water flush system for manure handling; the manure water is eventually mixed with freshwater and applied to cropland during irrigation. Good performance during irrigation applications is important due to the nutrients in the manure water. This project evaluated alternative management techniques (furrow torpedoes, surge irrigation and shortening furrow lengths) for improving irrigation practices on dairies. All three techniques reduced the amount of water required for irrigation. The project also investigated the impact of changing the timing of manure-water additions to the fresh irrigation water. Delaying the addition of manure water until the advancing fresh irrigation water had reached approximately 80% of the distance down the field improved nutrient-application uniformity and reduced nutrient applications.

In the first evaluation of its kind, we found that the UC Cooperative Extension (UCCE) 5-day degree-day forecast for cotton-planting conditions performed well in Bakersfield and Fresno when compared with the actual, observed temperatures from 1998 to 2002. In most cases, the forecast provided timely advice during the critical cotton-planting period. On average, only 7% of the forecasts failed to predict unfavorable conditions. Better-than-expected weather occurred 9% of the time when unfavorable conditions were forecast. On average during the 22 planting days of March (beginning March 10, the first allowable planting date in the San Joaquin Valley), 2.5 days (11%) were incorrectly forecast to have better-than-unfavorable planting conditions. In April, the cotton-planting forecasts were more reliable, with only 1 day out of 30 (3%), on average, that may have required replanting because of unpredicted, unfavorable conditions.

California kiwifruit is one of several commodities with a federal marketing order covering both conventional and organic products. Organic kiwifruit handlers were asked for their views on marketing issues for organic kiwifruit and how they differ from those for conventional kiwifruit. Organically produced kiwifruit accounted for 6.1% of total 2001-2002 California kiwifruit production. There are several differences between organic and conventional kiwifruit. The average size of organic kiwifruit is smaller than conventional kiwifruit; sales tend to occur later in the marketing year; there are more intermediaries (middlemen) in the marketing channel; and a larger proportion of organic product is packed in smaller shipping containers. The traditional price premium for organic product is decreasing as organic production increases, and it is not unusual for organically produced kiwifruit to be sold as conventional fruit in conventional marketing channels. Product appearance is becoming more important to consumers of organic fruit, who are now less willing to pay premium prices for cosmetically challenged product.