Decomposition Rates and Nutrient Release of Three Legume Cover Crops in an Organic Farm System.

Cover crops act as green manure adding nutrients to the soil. For green manure crops to be effective N sources for organic farming systems, their N release must be in synchrony with crop N demand. In this study, we assessed the decomposition rates and chemical composition of three cover crops (soybean, red clover, and white clover) in a certified organic field. Cover crop biomass samples were taken and air dried in the fall and spring, respectively. Litterbags containing 4g of air dried plant material were buried at a depth of 15 cm in the soil in December and March, simulating fall termination and spring termination of cover crops. Considering that temperatures in the first 8 weeks following fall burial were low and soil was frozen, the nine extraction times for the fall treatment were 0, 12, 16, 20, 24, 28, 32, 40, 48 weeks after burial. For the spring treatment, samples were extracted every four weeks beginning on February 27. Soil samples from each block were taken at the same time. Extracted litterbags were oven-dried and samples were analyzed for biomass fractions (soluble, hemicellulose, cellulose, and lignin) and total C and N content. From the initial analysis results, soybean contains most N and has the most mass-lost. We hypothesize that: (1) the three target crops will have different performances according to their chemical properties; (2) soybean will contribute the most N into soil; and (3) most N will be released in earliest stage of decomposition.