Long-term effects of biochar addition and straw return on N2O fluxes and the related functional gene abundances under wheat-maize rotation system in the North China Plain.

Graphical abstract The cumulative N 2 O emissions of CK, C1, C2, and SR treatments during the maize/wheat growing seasons of 2013–2014 (a) and 2014–2015 (b). Highlights • Low doses of biochar addition increased N 2 O emission. • High doses of biochar addition reduced N 2 O emission. • Biochar increased soil pH and the abundances of ammonia oxidizers and denitrifying genes. • Straw return increased N 2 O emission. • Application of biochar, instead of straw return, is a more optimum agricultural strategy in the wheat-maize system. Abstract To evaluate long-term effects of biochar addition and straw return (SR) on N 2 O fluxes in wheat-maize rotation system, a 2-year field experiment following a 7-year biochar addition and SR was investigated in an intensively managed agricultural soil in the North China Plain (NCP). Four treatments were included: 1) no biochar addition (CK); 2) biochar treatment with 4.5 t ha−1 yr−1 (C1); 3) biochar treatment with 9.0 t ha−1 yr−1 (C2); and 4) all the wheat/maize straw return (SR). The results showed the annual cumulative N 2 O emissions from C1 treatment were increased by 15.9–16.5%, while C2 treatment suppressed the annual cumulative N 2 O emissions by 22.8–26.3%. In comparison, straw return suppressed N 2 O emissions by 13.4–43.6% in the wheat season but increased N 2 O emissions remarkably by 45.3–53.9% in the maize season. Biochar addition enhanced the copies of AOA, AOB, nirK , nirS , and nosZ genes, while straw return decreased the copies of AOB, nirK , nirS , and nosZ genes at the high N 2 O emission period in the maize season. The production of N 2 O in the maize season was mainly driven by the AOB and nosZ genes, and by AOB gene in the wheat season. These results suggest that application of 9.0 t ha−1 yr−1 biochar is a more optimum agricultural strategy for reducing N 2 O emission in the wheat-maize system. [ABSTRACT FROM AUTHOR]