Fixation and Release of Nitrogen From Novel Cover Crops for Use in Reduced Tillage Organic Corn Production in North Carolina.

Organic corn production is challenged by nitrogen (N) limitations and weed pressures. The common practice of incorporating legume cover crops for N supply to a following corn crop often leads to early N release with a resulting lack of crop-N synchrony, while cultivation to manage weeds often reduces organic matter and increases erosion. We hypothesized that a roller-crimper tool can be used to provide adequate N to a corn crop by roll-killing proceeding legume cover crops and leaving material as a surface mulch, and that legume cover crop species/cultivars will differ in the amount of N contributed and timing of delivery. Several recently developed early flowering species of winter annual legumes could be used in this system, as rolling is most effective at cover crop maturity. Fourteen winter annual legumes were planted at two sites in North Carolina in fall of 2008. Covers were roll-killed on 3 dates in spring 2009 and corn planted into the mulch. Rolled cover crop tissue was collected and analyzed for total biomass, total N, and C:N ratio. Percent N derived from the atmosphere through nitrogen fixation was determined at the optimal kill date for each legume using the ¹⁵N natural abundance stable isotope method. Mulch decomposition and N mineralization was determined for Vicia villosa and Trifolium incarnatum using Plant Root Simulator (PRS) ion resin probes to determine NH4+ and NO3- flux, combined with periodic soil sampling. Results showed vast differences in biomass production of legume species, with 4 hairy vetch (Vicia villosa) and 4 crimson clover (Trifolium incarnatum) species having significantly greater biomass than other species.  Nitrogen availability following cover crop roll-down was significantly greater for hairy vetch than for crimson clover, as determined by PRS probes.