CAL-Collaborative Organic Research and Extension Network: On-farm Research to Improve Strawberry/Vegetable Rotation Systems in Coastal California

CAL-CORE is a network of researchers, farmers, extension professionals, industry and non-profit organizations dedicated to furthering research into organic strawberry and vegetable production in coastal California. Formed 9 years ago, we have worked on a variety of fertility, pest and disease management issues facing organic growers.  Currently, our main effort centers on vegetable/strawberry rotations and different options for fertility and disease management. In a replicated field trial we compare treatments across a range of sustainability criteria: crop yield, nitrogen cycling and losses, greenhouse gas emissions, disease incidence, biocontrol of insect pests, soil carbon pools, and economics. Ultimately a full life cycle analysis for each rotation system will be developed to assess their overall environmental foot print. Main treatments are 2 versus 4 year rotations with different crop combinations believed to be either suppressive of a major soil borne disease (Verticillium wilt), or more profitable but more conducive to disease.  Superimposed on the rotations are fertility treatments (legume/cereal cover crop only, legume/cereal cover crop + compost + additional fertility amendments, cereal cover crop + mustard seed meal, or untreated control) and in the two legume/cereal cover cropped treatments Anaerobic Soil Disinfestation (ASD, a promising option for controlling a range of soil borne diseases) is used for disease management prior to planting strawberries. Six network farmers also chose a sub-set of these treatments to test on their farms and compare to their own management practices. The study is in year 4 and all treatments at all locations are now planted to strawberries. Preliminary data on system productivity, nitrogen cycling greenhouse gas emissions, soil carbon, plant disease and biocontrol of cabbage aphids will be presented. Findings to date demonstrate: good production levels in all treatments, modest control of strawberrry disease in year 2 of the 2 year rotation in the ASD treated plots; greater soil C loss in the bare fallow treatments and following strawberries; significant biological control of cabbage aphid on broccoli by syrphid fly larvae; low levels of greenhouse gaas emission in general but increased rates following cover crop incorporation.  This project will provide farmers with tools to improve their production systems, meet water quality regulations, and quantify climate-related impacts of these intensive organic systems.