Cover crops act as green manure adding organic matter to agricultural-soils. For legume green manures to be an effective nitrogen (N) source for organic farming systems, their N release must be in synchrony with crop N demand. The objectives of this study were 1) determine the decomposition rates of three common cover crops (white clover, (Trifolium repens,L ) red clover (Trifolium pratense L.) and soybean (Glycine max L) in order to determine when most N was released and its synchrony with subsequent corn crop uptake; 2) we focused on the effect of cover crops on soil N levels. This study was conducted in a certified organic field, near Mead, NE. We assessed the decomposition rates and chemical composition of three cover crops with different incorporation time (fall and spring). Cover crop samples were taken and air dried in fall and spring. Litterbags containing plant samples were buried at a depth of 15 cm in December, 2011 and March, 2012. The nine extraction times for fall treatment were 0, 12, 16, 20, 24, 28, 32, 40, 48 weeks after burial. For spring treatment, samples were dug up every four weeks. Soil samples from each experimental unit 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. As conclusion, decomposition rates of five treatments follow the order: white clover incorporated in spring\u3e red clover incorporated in spring\u3e white clover incorporated in fall\u3e red clover incorporated in fall\u3e soybean incorporated in fall. Mass loss, nutrient content, and litter quality were all changed mostly in the first 0-3 months, which indicates that early stage of cover crops incorporation is critical to cover crop management. To describe the decomposition process, asymptotic models are more appropriate. Cover crops killed in spring have a better synchrony with corn uptake curve. After growing season, soil following red clover had greater level of soil nitrate-N.
Advisor: James R. Brandl
