Nitrous oxide emissions as influenced by legume cover crops and nitrogen fertilization
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2018, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply. In this study, we measured nitrous oxide (N2O) fluxes from plots of fall-planted hairy vetch (HV, Vicia villosa) and spring-planted broadleaf vetch (BLV, Vicia narbonensis) grown as nitrogen (N) sources for following summer forage crabgrass (Digitaria sanguinalis). Comparisons also included 60kgha1 inorganic N fertilizer for crabgrass at planting (60-N) and a control without N fertilizer. Each treatment had six replicated plots across the slope. Fluxes were measured with closed chamber systems during the period between spring growth of cover crops and first-cut of crabgrass in mid-July. HV had strong stand and aboveground biomass had 185 50kgNha1 (mean standard error, n = 6) at termination. However, BLV did not establish well and aboveground biomass had only 35 15kgNha1. Ratio vegetation index of crabgrass measured as proxy of biomass growth was highest in HV treatment. However, total aboveground biomass of crabgrass was statistically similar to 60-N plots. Fluxes of N2O were low prior to termination of cover crops but were as high as 8.2kg N2Oha1day1 from HV plots after termination. The fluxes were enhanced by large rainfall events recorded after biomass incorporation. Rainfall enhanced N2O fluxes were also observed in other treatments, but their magnitudes were much smaller. The high N2O fluxes from HV plots contributed to emissions of 30.3 12.4kgN2Oha1 within 30days of biomass incorporation. Emissions were only 2.0 0.7, 3.4 1.3 and 1.0 0.4kg N2Oha1 from BLV, 60-N and control plots, respectively.
