|Spargo, John - Pennsylvania State University|
|Ackroyd, Victoria - North Carolina State University|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2016
Publication Date: 7/14/2016
Citation: Spargo, J.T., Cavigelli, M.A., Mirsky, S.B., Meisinger, J.J., Ackroyd, V. 2016. Organic supplemental nitrogen sources for field corn production after a hairy vetch cover crop. Agronomy Journal. 108:1992-2002.
Interpretive Summary: Adequate information on managing legume cover crops and animal byproducts to balance nitrogen and phosphorus inputs and outputs in organic systems is lacking for many areas of the United States, especially the Mid-Atlantic region. We conducted a two-year field study to test the hypothesis that supplementing hairy vetch with animal byproduct amendments approved for use in organic systems would: 1) increase corn grain yield, biomass, and nitrogen uptake compared to relying solely on a legume cover crop while 2) balancing phosphorus input and removal rates and minimizing end of season soil nitrogen. Results show that the benefits of integrating a legume cover crop and four different animal byproducts depend strongly on the performance of the cover crop. In one year when hairy vetch produced a lot of biomass, neither organic amendments or mineral fertilizers increased corn yield further, indicating that vetch alone can meet all of corn’s nitrogen needs. In a different year, poor vetch performance due to a winter kill event resulted in no benefit from vetch. Organic amendments that year increased corn grain yield but did not raise concerns of soil P buildup or residual soil N at applied rates. While field performance of the four organic amendments was very similar, costs differed substantially such that economic returns to poultry litter would be substantially greater than to pelletized poultry litter, a pelletized poultry litter-feather meal blend, or feather meal. These results will be of interest to organic and conventional farmers who use a hairy vetch cover crop, and to policy makers and government agencies concerned about balancing production and environmental issues in agriculture.
Technical Abstract: The combined use of legume cover crops and animal byproduct organic amendments could provide agronomic and environmental benefits to organic farmers by increasing corn grain yield while optimizing N and P inputs. To test this hypothesis we conducted a two-year field study and a laboratory soil incubation in Beltsville, MD, to characterize the N-mineralization dynamics of four animal byproduct N sources approved for use in organic systems (feather meal, FM; poultry litter, PL; pelletized poultry litter, PPL; and poultry litter-feather meal blend, PFMB) and determine their impact on corn grain yield when applied in the presence or absence of a hairy vetch cover crop. Results show that the benefit of integrating a hairy vetch cover crop with animal byproducts (applied to supply 45 kg N ha-1) is strongly dependent on the success of the legume cover crop. In 2010, vetch, which produced a biomass of 4630 kg ha-1, contributed 106 kg N ha-1, and increased corn N uptake by 76%, biomass by 26%, and grain yield by 53% compared to a no vetch treatment. None of the organic amendments (or ammonium nitrate applied at up to 270 kg N ha-1 in an associated conventional N fertilizer response curve) increased yield further. These results indicate that vetch alone supplied sufficient N to achieve maximum corn grain yield. By contrast, in 2009, vetch production was very low (1551 kg ha-1) due to a winter kill event and vetch provided no benefit to soil N availability or corn N uptake, biomass or grain yield. The four organic amendments—despite substantially different chemical and N release characteristics—increased corn grain biomass and N uptake by an average of 31 and 20%, respectively, whether vetch was present or not in 2009. With the exception of PPL, the organic amendments increased corn grain yield by an average of 27%. In all organic amendment treatments, P inputs were similar to or lower than P removal in corn grain harvest and residual soil N was very low, indicating that these application rates are environmentally sustainable. While field performance of the four organic amendments was very similar, costs differed substantially such that economic returns to PL would be substantially greater than for PPL, PFMB and FM.