Cover crop effects on nitrous oxide emissions from no-till cropland in Maryland

Authors: SEDGHI, NATHAN - University Of Maryland; Cavigelli, Michel; WEIL, RAY - University Of Maryland

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2024
Publication Date: 1/10/2024
Citation: Sedghi, N., Cavigelli, M.A., Weil, R.R. 2024. Cover crop effects on nitrous oxide emissions from no-till cropland in Maryland. Science of the Total Environment. Article e169991. https://doi.org/10.1016/j.scitotenv.2024.169991.
DOI: https://doi.org/10.1016/j.scitotenv.2024.169991

Interpretive Summary: While cover crops reduce nitrate leaching after cash crop harvest, their impact on emissions of nitrous oxide, an important greenhouse gas, are mixed. An ARS researcher with University of Maryland colleagues measured direct and estimated indirect emissions of nitrous oxide in two field experiments conducted on both a sandy and a silty soil. One experiment compared emissions during and after a radish-crimson clover-rye cover crop mix compared to a no cover and a radish only treatment. The other compared the impacts of cover crop planting date on emissions. Researchers found that nitrous oxide emissions were almost eight times greater at the silty than the sandy sites due to greater soil moisture retention. Greater nitrous oxide emissions followed radish winter-kill when radish biomass was high. Indirect nitrous oxide emissions were decreased about 7% by planting cover crops and by about 70% by planting cover crops early. On the silty soil, nitrous oxide emissions following fertilizer application were more than eight times greater than all previous nitrous oxide emissions, indicating that nitrogen fertilizers were a much more important source of nitrous oxide than cover crops . Results suggest that management to mitigate nitrous oxide emissions should consider soil texture and nitrogen fertilizer applications; cover crop management might be a secondary consideration. These results will be of interest to NRCS and other agencies working to reduce greenhouse gas emissions from agriculture.

Technical Abstract: Cover crops reduce nitrate leached after cash crop harvest, but effects on nitrous oxide (N2O) emissions are mixed. Cover crops can reduce N2O emissions by reducing levels of mineral nitrogen (N) and water in surface soils during spring. Cover crops can also increase N2O emissions by adding organic substrates, releasing N during decomposition, or increasing soil water content during summer. Winter-killed cover crops can increase organic matter and soluble N during periods of typically low microbial activity. We hypothesized that planting a cover crop mix of radish (Raphanus sativus)-crimson clover (Trifolium incarnatum)-rye (Secale cereale) would increase direct N2O emissions relative to no cover crop, and result in lower direct and indirect N2O emissions than planting radish alone. We also hypothesized that extending the cover crop growing season, by planting earlier and killing later, would increase direct N2O emissions during winter, decrease direct N2O emissions during summer, and decrease indirect N2O emissions. To address these hypotheses, we conducted two field experiments (on sandy and silty soils) over four site-years. We measured cover crop biomass and N content, soil mineral N concentrations, soil moisture, green canopy cover, soil porewater nitrate, direct N2O emissions, and estimated indirect N2O emissions. Nitrous oxide emissions were ~7.8 times greater at the silty than the sandy sites due to greater soil moisture retention. Greater N2O emissions followed radish winter-kill at site-years with higher radish biomass. Indirect N2O emissions were decreased ~7% by planting cover crops and by ~70% by planting cover crops early. Soil texture had a large effect on N2O emissions, with fertilizer induced emission peaks being 8.2 times greater than all previous N2O emissions combined at a silty site. Results suggest that management to mitigate N2O emissions should consider soil texture and N fertilizer applications; cover crop management might be a secondary consideration.