Study On N₂O And NO Emission Characteristics From Long-term Fertilization Cropland In Guanzhong And Simulating N₂O Emission Dynamics By Model

Nitrous oxide?N₂O?is a potent greenhouse gas and the single greatest ozone-depleting substance.The atmospheric concentration of N₂O has increased by 20%since the preindustrial period.Nitric oxide?NO?is an atmospheric pollutant that participates in the formation of acid rain,photochemical smog,and tropospheric ozone.Agricultural soil is a major source of anthropogenic N₂O and NO,mostly as a result of the usage of nitrogen?N?fertilizers.Soil N₂O and NO are primarily produced by microbial nitrification and denitrification processes.Application of organic materials reduces the usage of chemical fertilizers,promotes soil fertility and grain yield,and regulates N₂O and NO emissions by affecting the activity of soil microbes and availability of C and N substrates.Impact of application of organic materials on N₂O and NO emissions generally displayed large variances in previous studies,mostly due to differences in field management,weather conditions,and monitoring methods.Guanzhong Plain lies on the south edge of Loess Plateau.Application of organic materials is widespread in Guanzhong Plain to protect soils from degredaion.It is necessary to quantify the effect of application of organic materials on N₂O and NO emissions in Guanzhong Plain.The primary aims of this study were to quantify N₂O and NO emissions from winter wheat-summer maize cropping systems following long-term application of dairy manure and crop residues,and to test the ability of NOE model for simulating N₂O emissions.Fild experiments were conducted in a 27a long-term fertilization cropland on the“Chinese National Soil Fertility and Fertilizer Efficiency Monitoring Base of Loessial Soil”.Fertilization regimes include an unfertilized control?CK?and three fertilized treatments:chemical fertilizer?NPK?,chemical fertilizer plus dairy manure?NPKM?,and chemical fertilizer plus crop residues?NPKS?.Soil N₂O and NO fluxes were measured from June 2017to June 2018 using static chambers.NOE is a non-linear and semi-empirical model that simulates N₂O emission through nitrification and denitrification on a daily step.Input parameters include soil temperature,humidity,and carbon and nitrogen substrate concentration.Major results are as follows:?1?N₂O and NO fluxes varied largely from-0.5 to 265.4 and from-1.2 to 70.8 g·?hm²·d?^-1,across the fertilized treatments,with emission peaks following irrigation and fertilization.The highest N₂O and NO fluxes occurred in NPKS and NPKM treatmets,respectively,in summer maize season.N₂O and NO fluxes were low from CK treatment,with the highest values being 11.6 and 7.6 g·?hm²·d?^-1,respectively.?2?Compared with NPK,long-term application of manure has no significant effect on N₂O emissions,but significantly increases NO emissions.Long-term returning straw has a significantly increased N₂O and NO emissions.Annual N₂O emissions from CK,NPK,NPKM and NPKS treatments were 0.21,2.32,2.15 and 4.59 kg·hm^-2,respectively;Annual NO emissions were 0.23,0.80,1.46 and 1.34 kg·hm^-2,respectively.The N₂O annual direct emission factors from NPK,NPKM and NPKS treatment were 0.60%,0.55%and 1.11%,respectively;and the NO annual direct emission factors were 0.16%,0.35%and 0.28%,respectively.?3?Pearson correlation analysis showed that NO flux and N₂O+NO flux in each treatment had a positive correlation with soil temperature.Boundary line analysis showed that N₂O and NO fluxes were significantly related to soil temperature and water content,and the optimal temperatures for N₂O and NO emissions are 20.0?and 26.3?,respectively.When the soil temperature exceeds 20?,the NO/N₂O ratios of NPK,NPKM,and NPKS treatments negatively correlated with water content.This finding suggests that soil temperature and water content regulated the NO/N₂O flux ratio and modified the relative importance of nitrification and denitrification processes.?4?Simulation of NOE model largely presented the seasonal vairations in N₂O emissions across the treatments,with r² ranging from 0.14 to 0.54?P<0.01?.Simulation bias in annual N₂O emissions ranged from-66.7%to 14.4%.Approaches to improve the model were suggested.