Nitrous oxide emissions from manured, no-till corn systems

Using dairy manure and legumes in crop rotations can reduce inorganic N inputs for corn ( Zea mays L.), yet these practices can also contribute to nitrous oxide (N 2 O) emissions. In two crop rotations we investigated how different (i) organic and inorganic N amendments and (ii) prior legume crops with broadcast manure influenced direct N 2 O emissions from silt-loam soils planted to no-till corn. We measured N 2 O fluxes from April to December for two years using closed vented chambers from soils planted to corn with no spring residue to compare inorganic N fertilizer (S-UAN) and two liquid dairy manure application methods: surface broadcasted (S-BM) and injected (S-IM). Emissions were also measured to compare the effect of crop residue of perennial forages, a green manure legume, or soybean ( Glycine max L. Merr.) from soils all amended with liquid dairy manure. Nitrous oxide emissions were greatest during the 15–45 days after manure was injected compared to broadcasting, and cumulative N 2 O emissions were larger from S-IM (2.8–2.5 kg ha −1 ) than S-BM (1.4–0.7 kg ha −1 ) and S-UAN (0.3 kg ha −1 ). Cumulative and yield-scaled N 2 O emissions did not differ among the prior legume treatments. A ranking approach based on random forests, identified the most important variable contributing to N 2 O emissions in both comparisons as corn growing degree days, indicative of the asynchrony of spring legume termination and manure application with corn planting and N use; and changing environmental conditions for N mineralization and denitrification.