Objective:
Objective 1: Develop cover crop management practices to optimize efficient nitrogen release for vegetable production. Objective 2: Determine whether cover crops can be integrated with season-extending high tunnels to maximize production and profit potential of high-value crop production. Objective 3: Determine rhizosphere communities on tomato plants grown in hairy vetch and rye cover crops. Objective 4: Breed and evaluate new cultivars of (a) hairy vetch for use as a cover crop, (b) tall, large-seeded vegetable soybean cultivars for small farmers, and (c) grain type soybeans with enhanced crop residue production to reduce soil erosion. Objective 5: Develop low-input, no-tillage cover cropping systems for date palm orchards of southeast California and for sugar apple orchards of subtropical Florida.

Approach:
Several approaches for improving management and our understanding of cover crops that will contribute to production of high-value crops are addressed in this project. Important advances have been made in the past decade by the investigators of this project toward developing no-tillage, cover crop-based systems for horticultural crop production. Hairy vetch is a winter annual cover crop that has become a foundation for these systems, however, there are several refinements that will improve system performance. Although hairy vetch can release high quantities of nitrogen for succeeding crops, it may release this nitrogen too fast and result in nitrogen losses to groundwater or atmosphere similar to losses associated with fertilizer nitrogen. We propose to test whether a mixture of hairy vetch and rye in combination with killing by rolling rather than mowing and judicious use of overhead irrigation will manage nitrogen release to parallel that of crop uptake and thereby minimize losses (Objective 1). Many local growers are moving production of high-value crops into high tunnels, but are ignoring the need for rotations to build soil fertility and avoid diseases. We propose to adopt a system for tomato production using mobile high tunnels in association with adding legume cover crops to the rotation, adding compost amendments, and using a UV-B filtered covering to improve production, build soil fertility, and minimize crop pathogens and pests (Objective 2). Hairy vetch appears to stimulate growth of crops such as tomato by mechanisms other than simply providing nitrogen. We will address the hypothesis that a vetch cover crop creates favorable microbial populations in the vegetable crop rhizosphere that stimulate crop growth and delay senescence (Objective 3). Hairy vetch can only be killed effectively by mechanical operations such as mowing or rolling during flowering, however, vetch tends to flower later than is optimal for planting many crops. A breeding program has been initiated to combine traits for early flowering that are linked to poor winter-survival in current early cultivars with traits for winter-hardiness found in later maturing lines (Objective 4). In addition, continued development of new soybean lines as part of this objective also will contribute to the needs of high-value producers (edible soybeans) and soil conservation (high residue-producing grain soybeans). Finally, the Lead Scientist of this project will continue work initiated by invitation to develop cover crop systems for high-value crop orchards, date palm in southern California and sugar apple in subtropical Florida (Objective 5). We expect to develop cost-effective sustainable, integrated cropping systems using cover crops for use in American Agriculture.