AUTHOR=Singh Hardeep , Kandel Tanka P. , Gowda Prasanna H. , Northup Brian K. , Kakani Vijaya G. 

TITLE=N2O Emissions From Residues of Oat and Grass Pea Cover Crops Cultivated in the US Southern Great Plains

JOURNAL=Frontiers in Sustainable Food Systems

VOLUME=4

YEAR=2021

URL=https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2020.604934

DOI=10.3389/fsufs.2020.604934

ISSN=2571-581X

ABSTRACT=<p>Grass pea (<italic>Lathyrus sphaericus</italic>) and oat (<italic>Avena sativa</italic>) are potential cover crops for spring periods of summer crop systems in the US Southern Great Plains (SGP). The main objective of this study was to compare nitrous oxide (N<sub>2</sub>O) emissions from residues of grass pea and oat grown as green nitrogen (N) crops. The comparisons included responses from plots cultivated with oat, grass pea, and control (spring-fallowed) plots. Two management options were applied to grass pea: residues retained and aboveground biomass removed for forage. Crabgrass (<italic>Digitaria sanguinalis</italic>) was cultivated as a main summer crop immediately after termination of the cover crops. Fluxes of N<sub>2</sub>O were measured by closed chamber connected to a portable gas analyzer on 23 dates during a 3 month growing period for crabgrass. At termination, oat produced more aboveground biomass than grass pea (2.17 vs. 3.56 Mg ha<sup>−1</sup>), but total N in biomass was similar (102–104 kg ha<sup>−1</sup>) due to greater N concentrations in grass pea than oat (4.80% vs. 2.86% of dry mass). Three month cumulative emissions of N<sub>2</sub>O from grass pea-incorporated plots (0.76 ± 0.11 kg N<sub>2</sub>O-N ha<sup>−1</sup>; mean ± standard error, <italic>n</italic> = 3) were significantly lower than from oat-incorporated plots (1.26 ± 0.14 kg N<sub>2</sub>O-N ha<sup>−1</sup>). Emissions from grass pea plots with harvested biomass (0.48 ± 0.04 kg N<sub>2</sub>O-N ha<sup>−1</sup>) were significantly lower than those from grass pea-incorporated plots. Cumulative N<sub>2</sub>O emissions from control plots were significantly greater than those from grass pea-harvested plots but were similar to the emissions from grass pea-incorporated plots. Yields produced by crabgrass were similar from all cover crop treatments (8.65–10.46 Mg ha<sup>−1</sup>), but yield responses to the control (18.53 Mg ha<sup>−1</sup>) were significantly larger. Nitrogen concentrations in crabgrass were greater in response to oat- and grass pea-incorporated plots (2.86–2.87%) than in grass pea-harvested (1.93%) and control (1.44%) plots. In conclusion, the results indicated that (i) post-incorporation emissions of N<sub>2</sub>O can be greater from a non-legume green N crop than a legume green N crop due to greater biomass productivity of the cereal, and (ii) emissions of N<sub>2</sub>O could be mitigated by removing biomass of the green N crop for use as forage.</p>