Soil N 2 O emissions following termination of grass pea and oat cover crop residues with different maturity levels

Background: Although cover crops provide many agronomic and environmental benefits, they may also increase nitrous oxide (N 2 O) emissions after termination. The N 2 O emissions from decomposing biomass of cover crops largely depends on the type of cover and maturity level at termination. Aim: The objective of this study was to quantify N 2 O emissions following soil incorporation of a non‐legume (oat; Avena sativa L.) and a legume (grass pea; Lathyrus sphaericus Retz.) cover crop residues at two different maturity levels. Methods: Oat and grass pea were terminated at vegetative (early‐termination) and reproductive (late‐termination) stages, and stored fresh before soil incorporation (2.5 Mg dry matter ha −1 ) together in late‐May. A treatment with no cover crop was included as the control. The experiment was laid out as completely randomized block design with three replicated plots (2 m × 2 m) in each treatment combination. Finger millet [ Eleusine coracana (L.) Gaertn] seedlings were transplanted as a summer crop. The N 2 O fluxes were measured with a closed chamber with a portable gas analyzer on 25 dates over an experimental period of 98 days. Results: In general, fluxes of N 2 O increased after rainfall or irrigation events and approximated zero during dry periods. Cumulative N 2 O emissions during the 98 days study period were higher ( p < 0.01) from all cover crops treatments than the control. Effects of maturity level at termination on cumulative N 2 O emissions were significant ( p < 0.05) as 30–35% higher emissions were recorded from both cover crops terminated at the reproductive stage than the vegetative stage. Yields of finger millet biomass from oat incorporated plots were 15–19% greater ( p < 0.05) than grass pea incorporated plots, while the yields from control plots were not significantly different from plots receiving cover crop residues. Conclusions: Stage of maturity at termination alone was not a strong predictor of total cumulative N 2 O emissions from decomposing cover crop residues, as maturity level interacted with environment variables ( e.g ., timing of rainfall events).