Mowing cover crop on semi-permanent beds

Recently, California farmers have developed increased interest in alternative tillage and organic matter management practices, especially for intensive vegetable production, which is known to deplete soil organic matter (SOM). Sustainability issues, as well as the growing organic production industry, have prompted us to conduct several on-farm projects to assess the effects of tillage depth and intensity, and cover crops and compost for vegetable production in the Salinas Valley of coastal California.

Intensive year-round production for crops such as lettuce, broccoli, and celery occurs in the Salinas Valley is characterized by:

A mild climate and high inputs of irrigation and fertilizers, allowing the production of two or three crops per year. Large nitrate (NO₃^--N) leaching and denitrification losses; nitrate exceeds the public health standard (10 mg N L-1) in nearly half of the wells in the upper aquifer. Little return of organic matter to the soil after harvest of vegetables, but use of cover crops and compost has recently increased. Frequent tillage, ranging from single passes with cultivators for weed control, to disking, subsoiling and leveling a field between crops.

Participatory research with farmers on commercial fields provides an in situ opportunity to study management options, because results are:

• Typical ecological responses by the populations and communities of organisms within the actual agroecosystem, as compared to research station experiments that often cannot replicate the abiotic and biotic environment of real farms.
• Valuable directly to farmers who are stakeholders in the design and management of experiments.

Several recent projects in the Salinas Valley have emphasized on-farm research:

• Short-term responses to a single tillage event
• Soil food webs in legume-vegetable rotations with different tillage regimes Minimum tillage, cover crops, and compost
• On-farm comparison of three methods of reduced tillage