“Choosing and Managing Cover Crops to Improve Weed Management in Reduced Tillage Organic Vegetable Production”.

Reduced tillage can improve soil quality and reduce fossil fuel use.  However, weeds are a substantial challenge facing farmers interested in adopting organic reduced tillage.  A weed management tool for organic reduced tillage comes from growing cover crops over winter and then converting them into mulch.  Improving our understanding of cover cropping in reduced tillage organic farming is necessary to improve its accessibility and adoption.  With the goal to explore potential factors influencing weeds in cover crops, we examined ten annual cover crops (cereals, legumes, and blends) in western WA along with termination time (“early” or “late”) and termination method (roller crimper or flail mower).  We measured how soil nitrate, light penetration through mulch, and cover crop biomass might influence weed density in cover crop mulch in addition to how these factors differ among cover crop varieties.  The goal is to predict which cover crops are likely to be effective in the management of specific weeds in western Washington.  Our first year results indicate that rolling was more effective at limiting weed cover than was flail-mowing (p<0.001), whereas termination time did not influence weed cover.  Cover crop biomass production differed among cover crop treatments, with cereals the most productive.  Results from our light data suggest that although cover crops effectively block light over the season, weeds still grow through mulch.  Soil nitrate was not influential in explaining weed density.  There were few differences in specific weed species or annuals/perennials dicots/monocots among cover crop treatments.  Application of these results will help farmers determine which cover crops to use in combination with reduced tillage to improve weed management.