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A field experiment was conducted during the 2003 growing season to evaluate the effect of multiple application rates of biosolids material on Sudan grass yield. Growers in the Mohave Valley region of the state have been using biosolids for the past several years principally as a source of nitrogen (N) and secondarily as a soil amendment. Mineralization rates vary widely based on environmental factors, in particular temperature and soil moisture. Little research been conducted in this particular growing region to refine recommended application rates. The objective of this study was to compare the typical agronomic rate that is currently recommended to several other rates and determine the effects on Sudan grass yield. Results showed that the current recommended application rates produced the greatest yield. However, due to space limitations and logistics, the study was laid out in large treated blocks and was not replicated. As such, definitive conclusions from results are difficult to draw.

4 pp. / Summer cover crops can add nitrogen to the soil, build up and maintain soil organic matter, suppress pest populations, mitigate soil erosion, and reduce nutrient leaching when they are used in Arizona vegetable systems. However, careful management is required since cover crops can modify the availability of soil nitrogen and other critical nutrients. The ratio between carbon to nitrogen (C:N) in decomposing cover crop biomass is a critical indicator of the overall process of breakdown and eventual release of nutrients. This article introduces five cover crops that could improve vegetable systems in Arizona. The mixtures of a legume and a non-legume cover crop species can also be planted to obtain desired C:N ratios to optimize the benefits of cover crops.

Field and lab experiments were conducted to determine the efficacy of sudangrass (Sorghum X drumondii (Nees ex Steud.) Millsp. & Chase) cover crop management techniques and soil solarization on important agricultural weeds and pathogens in organic strawberry production in Central California. Lab experiments assessed the time needed to kill weed seeds at temperatures typically achieved during soil solarization (40°C, 45°C, 50°C, 55°C, and 60°C) in California. Seeds tested included little mallow, redstem filaree, bristly oxtongue, annual sowthistle, common purslane, nettleleaf goosefoot, and redroot pigweed. Efficacy of simulated solarization temperatures differed between different species. Cool-season annuals annual sowthistle and bristly oxtongue were more susceptible to heat treatments than warm-season annuals common purslane, redroot pigweed and nettleleaf goosefoot. Hard seeded weed species little mallow and redstem filaree were the least susceptible to heat treatments. Annual sowthistle, bristly oxtongue and nettleleaf goosefoot were affected at all temperatures. Redroot pigweed and little mallow were not affected by temperatures below 40°C. Common purslane was not affected by temperature below 45°C and redstem filaree was not affect by any temperatures tested. Hours of exposure and percent mortality of weed seeds were used to create thermal death models for weed seeds. Field experiments were conducted at the Cal Poly Organic Farm in San Luis Obispo, CA testing the effects of soil solarization and sudangrass residues on weeds, Verticillium dahliae populations, plant health, and yields in organic strawberry production. Using a split plot design, sudangrass was grown, mowed and then developed into two treatments: surface mulch or incorporated into the soil. The sudangrass treatments and a control were tested with and without soil solarization (n=4). Maximum soil temperatures in solarized treatments were 53°C at a soil depth of 5 cm and 42°C at a soil depth of 15 cm. Solarization reduced weed biomass between 49.8 and 95.2% during the first 3.5 months after tarp removal (p=0.03), reduced Verticillium dahliae populations by 80.7% (p=0.01), reduced plant mortality by 54.9% (pV. dahliae populations (p=0.33) or yields (p=0.25). However, mulched treatments reduced weed biomass between 45.0 and 61.3% (p=0.03) compared to other sudangrass treatments. Results indicate solarization can be used in central coast organic strawberry production to reduce hand-weeding, disease incidence, and increase yields.