2002-2004 Specialty Crops Research Program
University of California

Principal Investigators: Eric Brennan, Michael Cahn, Steve Fennimore, Howard Ferris, Richard Smith and Laura Tourte

Project title: Effect of cover crop variety and seeding rate, and supplemental fertilization on yield, weed management, nitrate leaching, soil quality, and profitability of organic cool-season vegetable production on the Central Coast

Organic farming is one of the fastest growing agricultural sectors on the Central Coast. Cover crops are important in organic systems and affect crop yield, soil quality, nutrient cycling, nitrate leaching, and pest and disease management. The impacts of cover crops on nitrate leaching, and weed and soil fertility management in organic vegetable production systems in the Central Coast have received little attention. To address this lack of information, we propose a 2.5-year study on the USDA organic research plot in Salinas that is farmed by a commercial organic farmer. We expect that this research will help farmers (1) to better understand and reduce weed management costs, (2) to minimize supplemental fertilizer inputs, and (3) to reduce nitrate leaching in organic cool season vegetable systems on the Central Coast.

The annual rotation will include a winter cover crop treatment followed by a summer celery crop. Winter cover crops treatments include a bare winter fallow (control), or one of three cover crops (rye, legume/rye mix, mustard). The cover crops will be planted at the standard rate (1x) and high rate (3x), and subsequent celery crops will be fertilized at a low rate (112 kg nitrogen/hectare) and a high rate (224 kg nitrogen/hectare). A randomized complete block design with four replications will be used.
We hypothesize (1) that the higher cover crop seeding rates will increase cover crop biomass production, reduce weed biomass and seed production, and reduce nitrate leaching, (2) that nitrate leaching will be highest in the bare fallow followed by the legume/rye mixture, (3), that celery following the legume/rye cover crop will be less reliant on supplemental fertilizers, (4) that abundance of bacterial and fungal feeding nematodes will be correlated with cover crop biomass production.

The objectives are (1) to determine the effects of the cover crop and fertilizer treatments on cover crop and weed shoot biomass production, weed seed bank dynamics, nitrate leaching and water use during the winter, (2) to determine the effects of the cover crop and fertilizer treatments on yield, soil nitrogen dynamics, weed management, and nematodes during the subsequent vegetable crop, (3) to determine the effects of the cover crop and fertilizer treatments on production costs (material input, equipment, labor) and profitability of the subsequent vegetable crop, and (4) to demonstrate the effects of the cover crop and fertilizer treatments to farmers on the Central Coast.

The results will be delivered to farmers at biannual field days, presentations at UC Cooperative Extension meetings, and in UC Cooperative Extension publications. The study will be described in detail on the UC “Optimizing Soil Management for Cool Season Vegetables” web site. Project impact will be assessed through a cover cropping survey of Central Coast farms at the beginning and end of the project.