Study On The Charateristics Of Nitrogen Accumulation And Leaching In Typical Farmland Soil Aggregates Of North China

China is the country with the largest amount of nitrogen fertilizer application in the world.The problem of excessive and unreasonable application of nitrogen fertilizer is very serious,which not only causes the accumulation of nitrogen in the farmland soil,but also causes water pollution such as nonpoint source pollution.Due to the different climate,biology,parent material,rainfall and other factors,as well as the amount of fertilization,fertilization types and irrigation system in different soil type areas of northern China,the research on the accumulation and leaching characteristics of soil nitrogen in typical farmland type areas of northern China under different fertilization and irrigation treatment conditions can provide theoretical basis for scientific application of nitrogen fertilizer and reduction of nitrogen loss in farmland soils in northern China.In this study,four typical farmland soils in the north of china were selected as the research objects: black soil,brown soil,alluvial soil and yellow soil.The indoor simulation method was used to explore the accumulation and leaching characteristics of nitrogen in the typical farmland aggregates in the north of China and the relationship between the characteristics of soil aggregates and the status of soil nitrogen nutrients under different fertilization and leaching treatments.The results show that:No significant effect on the composition of aggregates between different fertilization and leaching intensities.Under different fertilization treatments,the nitrogen content and storage of aggregates in four soil fractions increased significantly and finally stabilized,among which the nitrogen content and storage of aggregates > 0.25 mm increased more(P < 0.05).With the increase of fertilization times,the proportion of inorganic nitrogen reserves in total nitrogen reserves of different soils increased with the increase of fertilization times.The results of the correlation analysis between soil nitrogen storage and soil physical and chemical properties showed that the adsorption characteristics of soil nitrogen may be affected by multiple factors and have no significant correlation with single physical and chemical properties.The difference of nitrogen contribution rate of four kinds of soil aggregates was mainly caused by the change of aggregates.The change of aggregate quantity caused by different fertilization treatments changed the contribution rate of nitrogen of different soil types.Different types of soil have different characteristics of nitrogen absorption and mineralization rate of inorganic nitrogen.Different fertilization strategies should be adopted for different types of soil.With the increase of leaching times,the nitrogen content and storage of aggregates of different grain sizes in black soil,brown soil,alluvial soil and yellow soil first decreased rapidly,then decreased rapidly,and finally tended to be stable.Under different leaching treatments,the soil nitrogen storage showed a decreased trend.Under 10 leaching treatments,the leaching rate of total nitrogen storage in black soil was 36.51%,the leaching rate of nitrate storage was 86.10%,the leaching rate of ammonium storage was 88.14%,and the leaching rate of total nitrogen storage in brown soil was 17.14%.The leaching rate of nitrate nitrogen and ammonium nitrogen was 92.91% and 76.86%,respectively.The leaching rate of the total nitrogen reserves of the alluvial soil is 35.32%,that of the nitrate nitrogen reserves is 91.38%,that of the ammonium nitrogen reserves is 51.31%;that of the total nitrogen reserves of the Yellow soil is 23.69%,that of the nitrate nitrogen reserves is 98.48%,and that of the ammonium nitrogen reserves is 92.64%.Variance analysis showed that different fertilization and leaching times and different soil types significantly affected the accumulation characteristics of soil nitrogen reserves(P < 0.01).There was a significant positive correlation(P < 0.01)between the total nitrogen storage of four soils and the number of 2-1 mm size aggregates,and a significant positive correlation(P < 0.05)between the total nitrogen storage of four soils and the number of 1-0.5 mm size aggregates.There was a significant positive correlation(P < 0.05)between the storage of ammonium nitrogen and the number of 5-2 mm and 2-1 mm size aggregates,and total nitrogen and ammonium nitrogen mainly existed in the size aggregates > 1 mm.There was a significant negative correlation(P < 0.01)between the total nitrogen storage and the number of < 0.25 mm size aggregates,a significant negative correlation(P < 0.05)between the ammonium nitrogen storage and the size of < 0.25 mm size aggregates,and a significant negative correlation(P < 0.01)between the size of < 0.25 mm size aggregates.This indicates that total nitrogen and ammonium nitrogen are mainly present in < 0.25 mm granular aggregates.The stability of soil aggregates was positively correlated with the stability of 5-2 mm and 2-1 mm aggregates(P < 0.01),but negatively correlated with 0.5-0.25 mm and 0.25 mm aggregates(P < 0.01).5-2 mm and 2-1 mm particle size aggregates play an active role in maintaining the stability of soil aggregate structure.Increasing the content of large aggregates in soil can improve the stability of soil aggregates,increase the potential of nitrogen fixation and improve soil fertility.