Response Of Nitrous Oxide Emission To Long-term Dairy Manure Amendment And Its Mechanism In Agricultural Soils In Guanzhong Plain

Agricultural soils are the largest anthropogenic nitrous oxide?N₂O?source.Soil N₂O is mainly produced via microbial nitrification and denitrification,which are primarily controlled by nitrogen substrates and soil aeration.Organic amendment is one of the traditional farmland managements and is widely used in modern agricultural production.Its effects on N₂O emission and denitrification are not well understood in Guanzhong Plain.The primary aims of this study were to quantify the variations in N₂O emission,evaluate their major controls,and clarify the underlying mechanisms in a winter wheat-summer maize cropping system.The field experiment was based on a long-term localizing fertilization experiment which began in autumn,1990.Four treatments were set up in the field.The control?CK?treatment was unfertilized throughout the years.Three fertilized treatments differed only in the winter wheat season:synthetic fertilizer(NPK,165 kg·N·hm^-2),synthetic fertilizer plus low(NPKML,50+115 kg·N·hm^-2)and high(NPKMH,75+173 kg·N·hm^-2)levels of dairy manure;they were all fertilized with synthetic fertilizer(188 kg·N·hm^-2)in the summer maize season.The N₂O fluxes were measured by using static chambers on an annual basis?October 2015 to September 2016?.The objective was to quantify the effect of manure amendments on N₂O emissions.The potential denitrification and N₂O/?N₂O+N₂?ratio were determined by using acetylene inhibition technique.The objective was to clarify the mechanism of N₂O emission.The results showed that:?1?N₂O fluxes ranged from-0.4 to 922.7 g·?hm²·d?^-1 across the treatments during the experimental period.Emission peaks occured following fertilization in the winter wheat season,and following the fertilization and irrigation in the maize season,with the largest fluxes in NPKMH treatment.?2?The N₂O fluxes were significantly correlated with the NO₃^--N content across the treatments in wheat season?P<0.05?.A significant correlation existed between N₂O fluxes and soil temperature in NPKML treatment on an annual basis?P<0.01?.?3?Differences in cumulative N₂O emissions were not significant?P>0.05?in winter wheat season.While the emissions of NPKML and NPKMH treatments were significant larger than that of NPK treatment?P<0.05?in the maize season.?4?A significant positive correlation existed between accumulative N₂O emission and N application rate in the winter wheat season,indicating that nitrogen input was the major control of N₂O emissions.The accumulative N₂O emission related significantly to soil organic carbon?SOC?content in the summer maize season,indicating that denitrification was the dominant source of N₂O emissions.?5?The annual N₂O emissions and the direct emission factors ranged from 0.25 to 3.75kg·hm^-2 and from 0.42%to 0.80%across the treatments,respectively.?6?The potential denitrification ranged from 1734.6 to 10673.0?g·?kg·h?^-1 and from1305.6 to 5114.4?g·?kg·h?^-1 before and after the maize harvest,respectively.The N₂O/?N₂O+N₂?ranged from 0.14 to 0.44.DOC promoted N₂O emission rate and potential denitrification,and affected N₂O/?N₂O+N₂?ratio.?7?The significant correlation between the measured N₂O fluxes and incubated potential denitrification suggest that denitrification was the major source of N₂O emission from winter-wheat and maize cropping system in Guanzhong Plain.