California Agriculture

Use of cover crops and compost increased soil quality in irrigated, intensive production of lettuce and broccoli in the Salinas Valley. These methods had the beneficial impacts of increasing soil microbial biomass, increasing total soil carbon and nitrogen, reducing surface bulk density and decreasing the potential for groundwater pollution as a result of nitrate leaching below the root zone. These soil benefits did not lead to lower yields and occasionally resulted in fewer weeds and lower lettuce corky root disease. Although surface minimum tillage reduced yields, it led to reduced potential for nitrate leaching below the root zone. Use of conventional tillage, cover crops, and compost produced high vegetable yields and acceptable net economic returns over a 2-year period, but broccoli was more profitable than lettuce under this regime. Understanding the trade-offs of various costs and benefits will help growers choose management practices that optimize economic and environmental benefits.