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Evaluating Termination Methods of Four Winter Annual Leguminous Cover Crops for Optimizing Nitrogen Synchrony.

Brown, Matthew Issac. 2012. North Carolina State University, M.Sc.

Abstract

In agroecosystems, synchronizing availability of legume nitrogen (N) to cash crop need is essential to efficiently utilize cover crops as a fertility source. Winter annual legume cover crop termination can be achieved through both tillage and non-tillage methods. However, the chosen approach may affect legume decomposition rate and consequent N mineralization by impacting availability to decomposer soil microorganisms. We predict that termination method in combination with biomass nitrogen content will govern rates of mineralization. Our objective is to evaluate various legume species and termination methods to determine nitrogen release rates in corn following winter annual legumes. In this study, four leguminous winter cover crop species, Austr ian winter pea, hairy vetch, and balansa and crimson clovers, were terminated using a roller-crimper, flail mower, disk, or an herbicide. Bi-weekly inorganic soil tests and Plant Root Simulator ion resin probes were used to measure plant available NO3- -and NH4 . Cover crop biomass, total carbon, and total nitrogen were measured for each species prior to termination. Mineralized nitrogen was most available from Austrian winter pea and hair y vetch across all termination methods at six to ten weeks after kill. Disked hairy vetch contributed the greatest plant available nitrogen amongst all 16 combinations. Biomass contributions of cover crops ranged from 2.4 Mg ha-1 to 9.7 Mg ha-1 in crimson clover and balansa clover, respectively. Crimson clover, Austria n winter pea, and hairy vetch averaged greater than 7 Mg ha-1 over three years. Balansa clover was the lowest contributor of both biomass and biomass nitrogen (2.4 Mg ha-1 and 40.3 kg ha-1, respectively). Hairy vetch had the greatest overall average biomass nitrogen of 226.4 kg ha-1, while Austrian winter pea averaged 188.71 kg ha-1 and crimson clover averaged 181.1 kg ha-1 . Corn yield was not consistent with inorganic and PRS™ probe measurements of nitrogen. Results show though termination technique in combination with cover crop species does influence nitrogen contributions from winter annual leguminous cover crops.