Effect Of Long-Term Fertilization On Soil Aggregation And Its Carbon And Nitrogen Fractions Under Dryland Winter Wheat Monoculture System

Soil aggregation is one of the most important indicators for soil fertility.Based on a 30-yr fertilization experiment,the effects of yearly continuous fertilization on soil aggregation were explored in a winter wheat monoculture system.Treatments were included as control without treatment CK,nitrogen fertilizer+organic fertilizer NM,nitrogen fertilizer+phosphate fertilizer+organic fertilizer NPM,nitrogen fertilizer+phosphate fertilizer NP,phosphate fertilizer P,nitrogen fertilizer N,organic fertilizer M,long-term bare land BL,phosphate fertilizer+organic fertilizer PM,the amount of nitrogen fertilizer was 120kg/hm~2,organic fertilizer was 75kg/t and phosphorus fertilizer was 26.2kg/hm~2.The main results are as follows:(1)Compared to CK,NP?NM?PM?NPM decreased soil bulk density and increased soil water content and field capacity in the top layers.A negative correlation was found between soil total porosity and bulk density under fertilization treatments.(2)Under different fertilization treatments,the content of soil aggregates in dry farmland was the highest in large aggregates and the lowest in middle aggregates.With the decrease of particle size,the soil aggregate content decreased at first and then increased,and the soil agglomeration effect under NPM fertilization treatment was the best.The geometric mean diameter and average weight diameter of soil aggregates were significantly increased under the treatments of N?NPM and PM.There was no significant difference in the fractal dimension of soil particle volume among different treatments.Combined application of organic fertilizer and chemical fertilizer can improve the stability of soil aggregates and change the degree of soil aggregation.(3)Compared with CK,the contents of soil organic carbon and total nitrogen in NPM?NP?PM and NM treatments increased with the decrease of the particle size of soil aggregates,the contents of total nitrogen and organic carbon in soil aggregates increased at first and then decreased,and their contents were the highest in the middle aggregates.NPM increased the content of particulate organic carbon and particulate organic nitrogen in soil aggregates,especially in medium aggregates,while the effect of only adding phosphate fertilizer was the worst.the content of microbial biomass carbon in soil aggregates treated with NPM was the highest,among which the middle aggregates had the best effect on the accumulation of biomass nitrogen and the worst on aggregates.Under different fertilization treatments,the contribution rate of organic carbon and nitrogen of soil aggregates increased at first and then decreased with the decrease of the particle size of soil aggregates,which was mainly concentrated in the middle aggregates.Among the particle sizes of soil aggregates,the organic carbon enrichment coefficient of large and medium aggregates treated with NM is the largest.Under different fertilization treatments,the ratio of soil carbon to nitrogen decreased with the decrease of soil aggregate size.There was a positive correlation between the content of soil total organic carbon and the content of organic carbon in each particle size agglomeration,among which the content of organic carbon in large and medium aggregates made the greatest contribution to soil total organic carbon.In the relationship between soil total nitrogen and different particle size aggregates,the content of nitrogen in large and medium aggregates was positively correlated with the content of soil total nitrogen,among which the content of nitrogen in large aggregates made the greatest contribution to soil total nitrogen.