The continued expansion of organic strawberry and vegetable production in California faces two key challenges: managing soil-borne diseases without synthetic chemical fumigants, and optimizing fertility management to balance input use with the protection of vulnerable habitats.

This project aimed to demonstrate the effects of diverse organic strawberry/vegetable rotations and integrated ecological practices on the overall health of the agroecosystem.

In 2001, a replicated on-farm trial was initiated in Moss Landing, California. The main treatment was the number of years between strawberry crops (five levels), with strawberry cultivar as sub-plots (two levels).  Ecological practices used included biofumigation with broccoli residues and mustard incorporation, compost application, using rotational crops that do not host Verticillium dahliae (spinach and broccoli), and selecting strawberry cultivars less susceptible to disease.

While the main treatment effects were assessed 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) were monitored throughout the five years.

During the first three years, strawberries, vegetables, and cover crops showed moderate yields and no significant disease issues. No significant yield differences were observed between any treatments during this period. Nitrogen monitoring in organic strawberries suggested: 1) the maximum nitrogen loss during the rainy season reached 214 kg ha-1, and 2) pre-plant plastic mulch application and adjusting basal/supplemental nitrogen rates can significantly reduce nitrogen loss during the rainy season while maintaining fruit yield.

Incorporating broccoli residue consistently reduced Verticillium dahliae propagule numbers in soils, whereas mustard incorporation did not. Furthermore, a major weed in the plot (Capsella bursa-pastoris) hosts Verticillium dahliae, indicating that weed management should be integrated with soil-borne disease management.