Soil texture, fertilization, cover crop species and management affect nitrous oxide emissions from no-till cropland.

Cover crops reduce nitrate leached, but effects on nitrous oxide (N2 O) emissions are mixed. Cover crops can reduce N2 O emissions by reducing levels of mineral nitrogen (N) and surface soil moisture during spring. Cover crops can also increase N2 O emissions by adding organic substrates, releasing N during decomposition, or increasing summer soil water content. Winter-killed cover crops can increase soluble organic C and 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 N2 O emissions relative to no cover crop, and result in lower direct and indirect N2 O emissions than planting radish alone. We also hypothesized that extending the cover crop growing season, by planting earlier and killing later, would increase direct N2 O emissions during winter, decrease direct N2 O emissions during summer, and decrease indirect N2 O 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 N2 O emissions, and estimated indirect N2 O emissions. Nitrous oxide emissions were ~ 7.8 times greater at the silty than the sandy sites due to greater soil moisture retention. Site-years with high radish biomass exhibited greater direct N2 O emissions than sites with low radish biomass following winter-kill. Indirect N2 O emissions were decreased ~7 % by planting cover crops and by ~70 % by planting cover crops early. Fertilizer induced emission peaks were 8.2 times greater than all previous N2 O emissions combined at a silty site. Our results suggested that soil texture and fertilization played an important role in direct N2 O emissions, while cover crop species, biomass, and timing played a more important role in NO3 leached, and thus, indirect N2 O emissions.