Organic Supplemental Nitrogen Sources for Field Corn Production after a Hairy Vetch Cover Crop

Abstract

Legume cover crops and organic amendments in combination could meet corn (Zea mays L.) nitrogen (N) needs while optimizing phosphorus (P) inputs. In a 2‐yr field study, we characterized the N‐mineralization dynamics and impacts on corn grain yield of feather meal (FM), poultry litter (PL), pelletized PL (PPL), and a PPL‐FM blend (PFMB) with or without a hairy vetch (Vicia villosa Roth) cover crop. The four amendments, which differed substantially in chemical and laboratory N‐release characteristics, provided corn yield benefits only when vetch biomass was low. In 2010, vetch produced 4630 kg biomass ha−1 and increased corn grain yield from 8.7 to 13.3 Mg ha−1 compared with a no‐vetch treatment. Vetch alone supplied sufficient N to achieve maximum corn yield as determined using an ammonium nitrate fertilizer response curve embedded within the organic amendment experiment. In 2009, vetch produced only 1551 kg ha−1 and provided no benefit to corn yield. Three of the organic amendments (all but PPL) increased corn yield by 1.8 to 2.3 Mg ha−1 whether vetch was present or not. Phosphorus inputs from amendments were similar to, or lower than, P removal in corn grain harvest, indicating that amendments would not result in soil P accumulation at these application rates. Amendment costs differed substantially such that economic returns using PL would be considerably greater than with PPL, PFMB, or FM. Results show that considering legume cover crop biomass is critical to determining organic amendment applications. Impact of organic amendments on corn grain yield depends on vetch biomass production. Organic amendments did not increase corn yield when vetch biomass was >4500 kg ha−1. Vetch provided no benefit to corn yield when biomass was <1600 kg ha−1. Organic amendments increased corn yield when vetch biomass was <1600 kg ha−1. Amendments applied at 45 kg N ha−1 did not raise concerns about residual P.