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Open Access Publications from the University of California

Volume 64, Issue 3, 2010

Issue cover


California communities deal with conflict and adjustment at the urban-agricultural edge

About 2.5 million agricultural acres are located adjacent or in close proximity to nonfarm residences in California, leading to widespread farm-residential conflicts. This exploratory study compared high- and low-conflict edges in four crop-growing communities in two counties. (A separate analysis of San Diego County in a sidebar compares two edge situations involving animal and nursery operations.) We present tentative generalizations about conflict variations, sources and solutions. High conflict levels were largely due to residents’ unfamiliarity with agricultural activities, although conflict levels were also related to specific farming practices. We also pose questions to guide further and more systematic research on the edge issue in California agriculture.

A new method is used to evaluate the strategic value of Fresno County farmland

Fresno County is a rich agricultural area that faces rapid urbanization and farmland conversion. The county is participating in a strategic, multi-county planning initiative aimed at making sustainable and regionally cohesive land-use decisions. To inform this effort, we conducted a farmland conservation assessment and identified strategic farmlands for prioritization in future conservation efforts. We identified environmental and human predictor variables that affect the viability of existing farmland, used a geographic information system (GIS) to integrate them, and created a countywide strategic farmland conservation map. We compared our analysis to status quo methods of prioritization and found that with our model the spatial output of highly valued farmland was shifted, narrowed and located adjacent to some of the county’s most urbanized areas. These findings are influencing growth policies and farmland conservation planning in Fresno County.

Mitigation techniques reduce sediment in runoff from furrow-irrigated cropland

Irrigation tailwater can transport sediments and sediment-associated agricultural pollutants to nearby waterways. To help protect the biota of surface waters, we evaluated the use of polyacrylamide (PAM, a synthetic material that flocculates sedi-ments when added to water), vegetated ditches and sediment traps to mitigate sediment losses from furrow-irrigated fields. In a 2-year study, liquid PAM injected into irrigation source water most effectively reduced suspended-sediment concentrations in runoff from different soil types. Dry tablet and granule PAM formulations were also effective, as long as their placement in the furrows promoted their dissolution in irrigation water. Vegetated ditches resulted in intermediate reductions in suspended sediments in tailwater. The sediment traps were limited in their effectiveness by insufficient holding time for fine-grained particulates to settle out of the runoff.

Dry-season soil water repellency affects Tahoe Basin infiltration rates

Lake Tahoe’s declining clarity makes the identification of runoff and erosion sources and evaluation of control measures vitally important. We treated relatively undisturbed, native, forested sites of 10% to 15% slope with surfactant and used a rain-fall simulator to investigate the effects of repellency. We compared infiltration measurements made by the simulator and a mini-disk infiltrometer (MDI). Runoff was produced by all plots with untreated water, but only two of 12 plots with surfactant. At volcanic soil sites, infiltration rates using surfactant exceeded those with water by only 20% when there was little litter cover, but with substantial litter the infiltration rates increased threefold. Similarly, at the granitic soil sites surfactant-enhanced infiltration rates were four times greater with scant litter, and eight times greater with substantial litter cover. Postsimulation soil moisture content and wetting depths were greater with the surfactant treatment. Excavations under surfactant treatments revealed that discontinuities in the soil’s hydrophobic organic layer resulted in preferential infiltration zones in the mineral soils below.

Survey examines the adoption of perceived best management practices for almond nutrition

Fertilizer use in California agriculture has been under recent scrutiny regarding its impacts on air, surface water and groundwater quality. In June 2007, we surveyed almond growers to assess their plant nutrition practices, identify opportunities for improvement, and target research and extension needs. The majority of respondents, particularly those with large almond acreages, used fertigation to apply nitrogen; applied nitrogen coincident with periods of maximal plant demand; and collected annual tissue samples for analysis. While the survey results suggested broad compliance with the best-available management practices and are likely to indicate good nutrient-use efficiency, they also suggested that growers are uncertain about current practices to monitor orchard nutrient status and would value additional information to enable greater precision in fertilization rates and timing.

Distinctive symptoms differentiate four common types of berry shrivel disorder in grape

There are several causes of shriveled fruit in vineyards, including sunburn, dehydration, bunchstem necrosis (BSN), and a recently described sugar accumulation disorder (SAD). Due to the similarities in fruit appearance these disorders are often confused with one another, but they can easily be distinguished by the location and/or composition of the shriveled fruit and by the condition of the rachis. Sunburn is typically exhibited only on berries that are exposed to direct sunlight, and BSN is typified by necrotic rachis tissue, with shriveled berries distal to the necrotic tissue. SAD berries exhibit low sugar content as well as concentration, whereas late season dehydration berries, as well as BSN berries, typically have normal to above normal sugar concentration. SAD berries exhibit lower berry weight, pH, and anthocyanins, as well as differences in many nitrogenous compounds compared to normally-developing fruit. In one location, SAD is expressed at the whole-vine level, but none of the commonly known pathogenic organisms (phytoplasmas, closteroviruses, fanleaf viruses, nepovirusesm, and fleck complex viruses) were found to be associated with SAD.