Tuesday, 8 November 2005
11

Maintaining Agroecosystem Health in an Organic Strawberry/Vegetable Rotation System (Part 4): The First Four Years.

Joji Muramoto1, Stephen R. Gliessman1, Steven T. Koike2, Carol Shennan1, Dan Schmida3, Robert Stephens4, and Sean L. Swezey1. (1) UC Santa Cruz, 1156 High St., Santa Cruz, CA 95064, (2) UC-Cooperative Extension, 1432 Abbott Street, Salinas, CA 93901, (3) Sandpiper Farms, P.O.Box 3597, Freedom, CA 95019, (4) Elkhorn Ranch, P.O.Box 270, Moss Landing, CA 95039

Continued growth of organic strawberry and vegetable production in California faces two challenges: soil-borne disease management without use of synthetic chemical fumigants, and fertility management to optimize fertility input use while ensuring protection of vulnerable habitats. The goal of this project is to demonstrate effects of diverse organic strawberry/vegetable rotations and integrated ecological practices on agroecosystem health. In 2001, we initiated a replicated on-farm trial at Moss Landing, California with number of years between strawberry crops as main plot (5 levels) and strawberry cultivar as sub-plot (2 levels). Ecological practices such as biofumigation with broccoli residues and mustard incorporation, compost application, use of vegetables that do not host Verticillium dahliae (spinach and broccoli) as rotational crops, and choosing strawberry cultivars that are less sensitive to disease are used in integrated manner. While the main treatment effects will be tested after the fifth year, soil health indicators (Verticillium dahliae propagule number, soil inorganic N, and other physicochemical indicators) and agroecosystem health indicators (yield, disease incidence, and nutrient budgets) will be monitored during all five years. In the first three years, strawberries, vegetables and cover crops had moderate yields and no major disease problems. No significant differences were found between any treatments in yields of any crops during the period. The N monitoring in organic strawberries suggested: 1) the maximum N-loss during the rainy season reached 214 kg/ha, and 2) pre-plant plastic mulch application and adjusting basal/supplemental N rates can significantly reduce N-loss during the rainy season while maintaining fruit yield. Broccoli residue incorporations consistently reduced Verticillium dahliae propagule number in soils, whereas mustard incorporations did not. Further a major weed (Capsella bursa-pastoris) of the plot hosts Verticillium dahliae, suggesting weed management is integrated with soil-borne disease management. Results from the fourth year will also be presented.

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