Measured Sustainable N Benefits of Cover Crop By Fall-Applied Poultry Litter Management Schemes in a Corn Production System.

Cover crops have the potential to increase sustainability of corn (Zea mays) production systems by reducing nutrient losses.  However, their ability to conserve nutrients from composted animal manure in addition to their ability to fix atmospheric N₂ deserve further attention.  This research focused on the fertilizer N equivalency of cover crops and fall-applied poultry (Gallus domesticus) litter (PL) in a minimum till corn production system. The experimental design was a randomized complete block in a 4² factorial arrangement of treatments involving 4 replications. Cover crop treatments included rye (Secale cereale), hairy vetch (Vicia villosa) and a rye + vetch combination with and without 2000 kg ha^-1 fall-applied PL. Five N rates from 0 to 224 kg N ha^-1 of broadcast ammonium nitrate were included to provide a fertilizer N equivalency index for the PL-cover crop treatments. Above-ground cover crop biomass and C and N content were measured in the fall and spring using a 0.14 m² subplot and immediately prior to termination using 4 replicates of a 0.25 m² subplot. Natural abundance ¹⁵N levels were determined on final cover crop harvest to estimate the contribution of biological N₂-fixation. Soil NO₃^- and NH₄⁺ were measured from corn planting through 30 days. Corn dry matter yield, N content, total plant N, grain yield and grain N content were determined and used to calculate fertilizer N equivalency of treatments. Results from 2014 showed a combination of vetch and PL provided the greatest cover crop residue N  (113 kg N ha^-1) while rye provided the least (26 kg N  ha^-1). Based on grain N yield in 2013, vetch and PL provided the equivalent of 29 kg N ha^-1, while rye resulted in a net loss of 12 kg N ha^-1. Grain N yield in 2014 showed that vetch and PL provided 85 kg N ha^-1 (almost 3 times the 2013 value), while a rye cover crop was equivalent to 8 kg N ha^-1 and all treatments resulted in a positive value.  Complete results will include two fully replicated years of data and will thoroughly explore the dynamics of organic N sources in a minimum till corn production system.