The Influence of Termination Techniques On Plant Available Nitrogen Mineralized From Winter Annual Leguminous Cover Crops.

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 a variety of means, including tillage and non-tillage methods. However, the chosen approach may affect legume decomposition rate and consequently N mineralization by impacting availability to decomposer soil microorganisms. We predict that termination method in combination with biomass nitrogen content will govern this mineralization rate. Our objective is to evaluate a range of 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 including Austrian 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 under Austrian winter pea and hairy vetch across all terminations at six weeks after kill.  Rolled hairy vetch contributed the greatest plant available nitrogen amongst all 16 combinations.  Biomass contributions of crimson clover were higher (7,528 kg ha^-1) than hairy vetch (6,555 kg ha^-1) and Austrian winter pea (5,813 kg ha^-1), which both contributed similar amounts of biomass to the system.  Balansa clover was the lowest contributor of biomass at 4,880 kg ha^-1.  Austrian winter pea and hairy vetch had the highest total nitrogen content (216 and 191 kg ha^-1, respectively), followed by crimson clover (177 kg ha^-1), and balansa clover (108 kg ha^-1).  Results thus far demonstrate that termination technique in combination with cover crop species does influence nitrogen contributions from winter annual leguminous cover crops.