Nitrogen Loss Pathways And Flux Analysis On Purple Soil Slope Farmland Under Different Fertilization Treatments

Nitrogen is of great significance to agricultural production.Nitrogen fertilizer can increase grain production and ensure food security.However,the massive use of nitrogen fertilizer in the actual production process has caused serious environmental pollution problems.How to reduce nitrogen pollution in the process of ensuring food production has become a global hot issue.Purple soil,as an important cultivated land in the middle and upper reaches of the Yangtze River in southwestern China,has typical research significance.In this study,through field observation experiments at the Yanting Station of the Chinese Academy of Sciences,nitrogen oxides,ammonia volatilization and runoff after fertilization under different fertilization treatments in purple soil wheat-corn rotation system were observed.High synthetic N,P,K fertilizer（HNPK）,The results were different between synthetic N,P,K fertilizer（NPK）,pig manure with synthetic NPK fertilizer（OMNPK）,crop residues returned with synthetic NPK fertilizer（RSDNPK）,and no fertilization CK treatment.Nitrogen oxide loss,runoff loss and ammonia volatilization combined with crop yields of purple soil slope farmland under different fertilization treatments were screened to optimize the fertilization measures RSDNPK treatment under the combined effect of nitrogen oxide slope nitrogen farmland nitrogen oxide emissions and nitrogen loss.The main findings are as follows:（1）Soil N₂O and NO emission fluxes from cropland of purple soil was-4.16 to94.6μg（N）·m^-2·h^-1,and-10 to 93μg（N）·m^-2·h^-1,during the winter wheat season,the NPK fertilization treatment showed an emission peak on the 12th day after fertilization,which was 39.23μg（N）·m^-2·h^-1,and the average emission rate was13.83μg（N）·m^-2·h^-1HNPK reached its peak emission on the 9th day,which was127.54μg（N）·m^-2·h^-1,and the average emission rate was 18.83μg（N）·m^-2·h^-1 The peak OMNPK emission occurred on the 7th day and reached a peak emission of 62.50μg（N）·m^-2·h^-1,with an average emission rate of 14.03μg（N）·m^-2·h^-1.The RSDNPK reached the 12th day.The peak emission was 78.84μg（N）·m^-2·h^-1,and the average emission rate was 10.08μg（N）·m^-2·h^-1.In the summer maize season,the range of N₂O emission fluxes from CK soil treated with fertilization and control was-4.13～23.1μg（N）·m^-2·h^-1,and the average emission flux was 5.89μg（N）·m^-2·h^-1.The emission fluxes of HNPK,NPK,OMNPK and RSDNPK was-5～2023,-3～167.0,-0.03～3719,-1～1579μg（N）·m^-2·h^-1,during the summer corn season OMNPK treatment reached the peak and maximum emissions on the 2nd and 5th days after fertilization Value,with peak values of 1314 and 3719μg（N）·m^-2·h^-1.HNPK reached its first peak on the second day after fertilization,with a value of 1664μg（N）·m^-2·h^-1,and the maximum emission on the fifth day was 2023μg（N）·m^-2·h^-1.RSDNPK reached its peak on the second day after fertilization,with a value of 1579μg（N）·m^-2·h^-1.There were significant differences in treatment discharge rates between different fertilizations in the wheat and corn seasons.The discharge rate was high in the first two weeks of fertilization,and then the downward trend was obvious.It stabilized about two weeks or so,and no significant emission peak was observed without fertilization.Fertilization is the main driving factor for the peak emission of nitrogen oxides in purple soil.（2）In the rainy season,runoff losses are mainly caused by soil runoff and surface runoff.Among them,soil runoff is the most important way of nitrogen loss.During the research,it was found that nitrate nitrogen is the main form of nitrogen loss.The annual nitrogen loss flux from surface runoff in NPK was 3.8 kg·hm^-2,and the nitrogen loss flux from soil flow was 73.2 kg·hm^-2.The annual loss of nitrogen flux was 77.0 kg·hm^-2,accounting for 27.5%of the annual nitrogen application rate.HNPK annual surface runoff nitrogen loss flux is 17.9 kg·hm^-2,soil midstream nitrogen loss flux is 58.4 kg·hm^-2,annual loss nitrogen flux is 82.1 kg·hm^-2,accounting for the whole 21%of annual nitrogen application.Application of organic fertilizer OMNPK,the annual runoff nitrogen loss flux was 19 kg·hm^-2,the soil nitrogen loss flux was 58.4 kg·hm^-2,and the annual loss nitrogen flux was 77.4kg·hm^-2.It accounts for 22%of the annual nitrogen application.Nitrogen loss flux from surface runoff of RSDNPK with straw return to field was 27.7 kg·hm^-2 nitrogen loss flux from soil midstream was 27.6 kg·hm^-2,and annual nitrogen loss flux was55.3 kg·hm^-2,accounting for 19.3%of the annual nitrogen application rate.（3）There were significant differences in N₂O and NO emissions from different fertilization treatments（P<0.05）.N₂O emissions can be controlled by adjusting the fertilization method.The N₂O content of HNPK,NPK,OMNPK,and RSDNPK treatment was significantly higher than that of CK treatment（P<0.05）.The cumulative annual emissions of N₂O and NO from the soil treated with straw return to the field were 1.44 kg·hm^-2 and 0.015 kg·hm^-2,which were significantly lower than those of NPK and OMNPK,which could effectively reduce nitrogen oxide emissions.Increased nitrogen oxide emissions compared to NPK treatment.The fertilization method had a significant effect on the nitrogen loss from the purple sloping farmland（P<0.05）.The application of straw returning to the field can effectively suppress the emission of nitrogen oxides.（4）The fertilization method had a significant effect on ammonia volatilization of different fertilization treatments in purple soil（P<0.05）.It was found in the study that the ammonia volatilization of winter wheat and summer corn were mainly concentrated in the first two weeks.>CK.The cumulative emission rate of corn seasonal ammonia volatilization was HNPK>NPK>RSDNPK>OMNPK>CK.The NPK ammonia volatilization accumulation was 27kg（N）·hm^-2,accounting for 9.6%of the nitrogen application rate.HNPK increased 1.18 times ammonia emissions,OMNPK and RSDNPK reduced 70%and 56%nitrogen losses caused by ammonia volatilization.（5）In the study of winter wheat and summer corn,OMNPK and RSDNPK have higher crop yields of 8954 and 9224 kg·hm^-2,respectively.Fertilization is the main factor affecting crop yield.We can improve the crop by adjusting the fertilization method.Yield.As the demand for food continues to grow,considering agricultural production and environmental friendliness,and choosing different optimized fertilization methods for sustainable production,the best way to fertilize the annual rotation of purple soil winter wheat and summer corn is to return straw to the field to handle RSDNPK.Compared with NPK fertilization,it increases crop yield by 6%and reduces nitrogen loss by 32%.Compared with OMNPK,it increases yield by 2%and reduces nitrogen loss by 23%.It is a fertilization method that can achieve unified yield and environment.