Soil N2O emissions following termination of grass pea and oat cover crop residues with different maturity levels

• Published in: Journal of plant nutrition and soil science Vol. 183; no. 6; pp. 734 - 744
• Main Authors: Singh, Hardeep, Kandel, Tanka P., Gowda, Prasanna H., Northup, Brian K., Kakani, Vijaya G., Baath, Gurjinder S.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-12-2020
• Subjects: Agricultural practices; Agronomic crops; Agronomy; Avena sativa; Biomass; biomass decomposition; C/N ratio; Cereal crops; Cover crops; Crop residues; Crops; Decomposition; Dry matter; Eleusine coracana; Emissions; finger millet; Fluxes; Gas analyzers; Grass peas; Lathyrus sphaericus; Legumes; Maturity; Millet; N mineralization; Nitrous oxide; Peas; Rainfall; Residues; Seedlings; Soils
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.202000239

Background: Although cover crops provide many agronomic and environmental benefits, they may also increase nitrous oxide (N2O) emissions after termination. The N2O 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 N2O 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 N2O 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 N2O increased after rainfall or irrigation events and approximated zero during dry periods. Cumulative N2O 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 N2O 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 N2O emissions from decomposing cover crop residues, as maturity level interacted with environment variables (e.g., timing of rainfall events).