OFRF project funding was awarded in Fall 2003. A final report describing project results was submitted in September 2005. A project summary was issued in OFRF's Information Bulletin No. 15.

Investigator: Joji Muramoto, Center for Agroecology and Sustainable Food Systems, University of California, Santa Cruz
Project location: California Central Coast

Organic strawberry/vegetable rotation experiment at Elkhorn Ranch, Moss Landing, California. Each plot consists of four beds of which middle two beds (between red lines) are used for sampling. A broken line indicates a border between sub-plots. The green area marks forty strawberry plants for fruit harvest data sampling.

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 the main plot treatment (5 levels) and strawberry cultivar as sub-plots (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 an 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-1, 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.

A strawberry plot right after a storm. Water in furrows contained ~10 mg kg-1 of nitrate N, suggesting surface runoff can be a major path for losing nitrate to the environment.