While research on cover cropping and compost application have surged in the past decade, organic growers are still struggling to maintain sufficient levels of available nitrogen (N) in vegetable cropping systems. Especially in semiarid regions like California, relying on N mineralization from banked reserves in soil organic matter has not provided enough N to support high crop yields competitive with conventional systems; an additional source of labile N may be needed during the season. A number of new soluble injectable OMRI-approved fertilizer products are now available but have not been independently evaluated, leaving growers uncertain about efficacy. We will use plots managed organically for 26 years as part of a long term cropping systems trial at UC Davis’s Russell Ranch facility to compare N uptake, fruit yields, and profitability of three representative types of organic liquid fertilizers (fish emulsion, compost tea, and microbial/amino acid injectables) via fertigation in organic tomatoes. In addition to the field experiment, we will perform incubations with the soils fertilized with the three products to evaluate whether they can not only enhance soil available N levels during the growing season, but also can stimulate and/or enhance nutrient cycling from organic matter of N, P, and K. We will work with a grower collaborator to interpret and articulate results so they are effectively communicated to growers. Findings will be disseminated widely via fact sheets, presentations at organic farming conferences, and outreach articles posted to the web, and in a field day and soil health workshop.
