Soil N2O emissions following cover‐crop residues application under two soil moisture conditions

Abstract

AbstractCover crops in rotation or intercropped with annual crops are important strategies to increase C and N input in agricultural soils. However, these practices may also enhance soil N2O emissions. The effect on N2O emissions may be dependent upon the biochemical composition of cover crop residues. A 47‐d incubation study was conducted to determine soil N2O emissions following the addition of residues from three summer legume species [pigeon pea (Cajanus cajan L. Millsp.), cowpea (Vigna unguiculata L. Walp.), lablab bean (Lablab purpureus)], one winter legume [vetch (Vicia sativa L.)], one winter monocotyledon [black oat (Avena strigosa Schreb.)], and maize (Zea mays L.) under two water‐filled pore space levels (40 and 70% WFPS). Short‐term peaks of N2O fluxes were observed after the addition of all crop residues, but were much greater under 70 than 40% WFPS (5.2 and 5133 µg N‐N2O kg−1 soil for 40 and 70% WFPS, respectively). Under both WFPS, significantly higher peaks were detected after the application of N‐rich legume residues (7.7 and 3,356 µg N‐N2O kg−1 soil under 40 and 70% WFPS, respectively) than after the application of grass residues (2.8 and 1,777 µg N‐N2O kg−1 soil under 40 and 70% WFPS, respectively). Cumulative soil N2O produced under 70% WFPS was approx. 110 times greater than under 40% WFPS. Soil N2O emissions increased linearly as residue N content increased. Soil N2O emissions also increased linearly as the content of the recalcitrant compounds lignin and polyphenols increased, because residues with high N content also had high lignin and polyphenols content. When the content of C and recalcitrant compounds were expressed on an N basis, soil N2O emission decreased linearly as residue C/N, lignin/N, polyphenol/N, and (lignin + polyphenols)/N ratios increased. Indices that include recalcitrant compounds on N basis may be useful for the selection of cover‐crop species with the least impact on soil N2O emissions. However, our results show that these ratio indices had similar correlation coefficients compared to C/N ratio, indicating that C/N ratio is an efficient index to predict soil N2O emission following cover crop application.