长期玉米秸秆还田对冬小麦-夏玉米种植体系NO排放的影响OA

Agroecosystems are a significant source of nitric oxide(NO)which serves as an air pollutant.There is an urgent need to quantify and control NO emissions from agroecosystems.The NO fluxes were measured in a long-term(since 1990)fertilized winter wheat-maize cropping system for two years(from October 2022 to October 2024).The aims were to quantify the responses of NO emissions to maize stalk incorporation and to identify the major regulatory factors.The field trials included an unfertilized control(CK),chemical fertilizers(NPK),chemical fertilizers combined with maize residues(NPKS).The CK treatment was not fertilized throughout the year.The NPK and NPKS treatments received the same amount of urea,with nitrogen application rates of 165 and 188 kg/hm2 in the winter wheat and maize seasons,respectively.All wheat straw and maize stalk were removed from CK and NPK at harvest.For NPKS,maize stalk(with a nitrogen application rate averaging 40 kg/hm2)was retained at the time of maize harvest while wheat straw was removed at the time of winter wheat harvest.The results showed that the NO fluxes were low in CK,while they always peaked following fertilization in NPK and NPKS.The boundary lines of NO fluxes followed a logistic model and a Gaussian model against soil temperature and water-filled pore space,respectively,and linear models against ammonium and nitrate concentrations.The CK,NPK,and NPKS treatments showed annual NO emissions of 0.18-0.19,0.31-0.81,and 0.65-1.10 kg/hm2,respectively.In the two winter wheat seasons,cumulative NO emissions of NPKS were either 60%lower or 28%higher than those of NPK.In the two maize seasons,cumulative NO emissions of NPKS were 60%-231%higher(P<0.05).Annual NO emissions of NPKS were 37%-113%higher than those of NPK(P<0.05).The enhanced NO emissions mostly occurred in maize seasons,which were attributed to the 20%higher soil organic matter content of NPKS than that of NPK(P<0.05).In maize seasons,the promoting effect of soil organic matter on NO fluxes may be amplified in a warm and humidity environment,while such effect may be weakened or overrode by low temperature and stalk incorporation in winter wheat seasons.With long-term maize stalk incorporation,annual NO emissions from the winter wheat-maize cropping system were significantly enhanced,and mitigation efforts need to focus on the maize season.