Location: Forage and Livestock Production ResearchTitle: Incorporation and harvest management of hairy vetch-based green manure influence nitrous oxide emissions Author
Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2019
Publication Date: N/A
Interpretive Summary: Legumes cultivated as green manure are major source of nitrous oxide (N2O) emissions after termination and soil incorporation. Therefore, management options are needed to mitigate N2O emissions of legume green manures. One potential management technique to limit N2O emissions from legume green manure residues would be removal of aboveground biomass for use as forage prior to soil incorporation. Such a decision on biomass harvesting can be developed based on total biomass N, potential biomass N mineralization rates, and the expected N requirements for following recipient crops. The harvested legume biomass could lower the risk of forage shortage for cattle in dry years, which are common in the southern great plains. This study reports findings from a field experiment where fall planted hairy vetch (HV) was either harvested or incorporated in the soil prior to planting of crabgrass grown for hay crops in early May. Fluxes of N2O were measured at 27 dates during a 2-month study period. Two-month cumulative emission of N2O from HV incorporated plots was three times those of HV harvested plots. However, crabgrass biomass yields, N concentrations and biomass N uptake were decreased significantly by harvesting HV. In conclusion, the results suggested that whereas removal of HV biomass for use as forage may significantly reduce N2O emissions, quantity and quality of the following recipient crop may be constrained.
Technical Abstract: In this study, we measured nitrous oxide (N2O) emissions from plots of fall-planted hairy vetch (HV, Vicia villosa) grown as a green nitrogen (N) source for following summer forage crabgrass (Digitaria sanguinalis). Two treatments were compared: (i) HV grown solely as green manure where all biomass was incorporated by tillage, and (ii) harvesting of aboveground HV biomass prior to planting of crabgrass. Fluxes of N2O were measured with closed chamber systems on 27 dates during a 2-month growth period of crabgrass after termination of HV in early-May. At termination, average aboveground biomass of HV was 4.6 Mg ha-1 with 146 kg N ha-1 content. The N2O emissions were as high as 66 g N2O-N ha-1 day-1 on one day after HV incorporation, but reached close to zero within a week. Emissions of N2O increased with subsequent rainfall and irrigation events from both treatments but emission peaks were not observed during rapid growth of crabgrass. Two-month cumulative emission of N2O (mean ± standard error, n = 4) from HV incorporated plots (921 ± 120 g N2O-N ha-1) was three times (P < 0.05) of HV harvested plots (326 ± 30 g N2O-N ha-1). However, crabgrass biomass yields, N concentrations and biomass N uptake were decreased significantly by harvesting HV. In conclusion, the results suggested that whereas removal of HV biomass for use as forage may significantly reduce N2O emissions, quantity and quality of the following recipient crop may be constrained.