Land Use History, Biodiversity and Environmental Quality
A land use transect from intensive agriculture to upland grazed grasslands in the Central Coast region of California points out large changes in soil microbial communities and soil nutrient dynamics on the same soil parent material in relation to land use. This comparison of different land use types on the same soil parent material, has allowed us to relate soil resource availability to microbial community composition and vegetation management. A farmscape study in Yolo County is showing how smaller-scale features such as hedgerows and riparian corridors affect farm-level productivity, nutrient cycling, and economic profitability, which will allow analysis of tradeoffs for land use decision making. These projects are focusing on how different land use types affect plant carbon inputs, soil microbial composition, activity, and depth distribution, and ultimately soil carbon sequestration.
Soil Biology in Restored Perennial Grassland
When non-native annual grasslands in California are re-vegetated with native California perennial bunchgrasses, changes in soil ecology are relatively minor. Although tillage is used to reduce the seed bank of annual plants initially, this has little longer-term effect on soil microbial biomass and activity. The soil microbial community composition of the restored sites, however, bear more resemblance to that of annual grassland than relict perennial grassland, indicating slower recovery of soil vs. vegetation to the management transition.
Mycorrhizae and Roots
The role of arbuscular mycorrhizae for plant nutrient uptake, soil nutrient retention and soil biology is being studied in tomato, using a mutant with reduced colonization. Organic farming systems are the focus of this work. The genetics of root architecture and deep water use by lettuce has also been studied, and showed that wild lettuce is a potential source of germplasm for breeding lettuce with lower water input requirements.
Nitrogen and Carbon Cycling in Organic Vegetable Production
Nitrogen transformations, soil microbial community composition, and other soil aspects of soil ecology are altered by organic production. Nitrification, ammonia-oxidizing bacteria, and rhizosphere effects are being studied to better understand cycling and retention of nitrogen in organic tomato production systems, in comparison with conventional production. In addition, an on-farm project monitored the successful transition to organic production on two vegetable farms in the Salinas Valley, California, and demonstrated sufficient plant N uptake with little loss of inorganic N.
Tillage and Organic Matter Management
Tillage and organic matter management have short- and long-term effects on soil microbial processes and soil quality parameters, as well as on yield, soilborne disease, weeds, and economics. Minimum tillage and no-tillage have been studied in California vegetable systems for their effects on soil food webs and soil carbon sequestration.