Effect Of Long-term Fertilization On Aggregate Distribution And Its Physical Protected Organic Carbon In A Loess Soil

It is important that understanding soil aggregate distribution and its physical protection of organic carbon affected by long-term fertilization,in order to set up rational nutrient management.In this study,35 years long-term experiment was applied to investigate soil aggregate distribution and its physical protection of organic carbon in a loess soil.Five treatments were included,which were control without nutrient input(CK),high and low rates of chemical fertilizers(N1P1 and N2P2),and high and low rates of organic manure(M1 and M2).Soil samples were collected at 0-10 cm and 10-20 cm soil layers and analyzed water stable aggregates and clay fractions(>2 mm,0.25-2 mm,0.053-0.25 mm and <0.053mm),aggregate associated organic carbon.The main results were as follows:Long-term fertilization significantly increased soil organic carbon content and carbon storage at 0-10 cm soil layer,and compared with M1,the soil organic carbon content increased obviously by 18.14% and the carbon storage increased by 8.92% obviously under M2.The carbon storage and carbon sequestration rate under M increased significantly compared with that under NP.However,at 10-20 cm layer,long-term fertilization had little effect on soil organic carbon content and carbon storage except M2 treatment.Long-term fertilization significantly affected aggregate distribution.At 0-10 cm soil layer,Fertilized treatments significantly decreased >2 mm aggregates and <0.053 mm silt clay fraction except N1P1.At 10-20 cm soil layer,N2P2 treatment significantly increased aggregates of 0.053-0.25 mm,but reduced 0.25-2 mm aggregate fraction.Other treatments had no obvious influence relative to CK.Long-term fertilization significantly affected aggregate associated organic carbon content.Content of organic carbon in soil aggregates was higher by about 30% at 0-10 cm soil layer than that at 10-20 cm soil layer.At 0-10 cm soil layer,fertilized treatments significantly increased aggregate associated organic carbon content over CK except N1P1.At 10-20 cm soil layer,NP treatments had no effect on aggregate associated organic carbon content relative to CK,but M treatments significantly increased aggregate associated organic carbon content in > 2 mm fraction.The soil organic carbon partitioning to aggregates' fraction at each soil layer is basically the same with the highest proportion in 0.25-2 mm aggregates and the least in <0.053 mm silt clay fraction.Long-term applications of chemical fertilizers did not significantly affect weight distribution of fractions in macro-aggregates at 0-10 cm soil layer.Applications of M significantly increased light fraction(fine POM)content by 267%-392% and 49%-116%.At 10-20 cm layer,N2P2 and M treatments significantly reduced the light fraction(fine POM)content.Moreover,M2 treatment also increased coarse particulate organic matter(cPOM)mass by 87%.Long-term fertilization had no effect on mineral bound organic carbon(MOC).At 0-10 cm depth,long-term applications of chemical fertilizers had no effect on organic carbon content in all fractions within macro-aggregates and their carbon storage.However,M treatments increased organic carbon content in all fractions within macro-aggregates and significantly increased light fraction organic carbon(fPOC)and micro particulate organic carbon(iPOC)storage by 9-10 times.At 10-20 cm soil layer,long-term applications of chemical fertilizers had no effect on organic carbon content in all fractions within macro-aggregates and their carbon storage except N1P1 which significantly decreased light fraction organic carbon content.Furthermore,long-term applications of chemical fertilizers significantly decreased storage of light fraction organic carbon.Organic manure(M)alone significantly increased fPOC and particulate organic carbon(iPOC)storage within micro aggregates compared to NP.The iPOC showed a significant positive correlation with soil organic carbon.Overall,long-term fertilization significantly affected soil organic carbon content and aggregate associated organic carbon content,especially at surface soil layer.Long-term fertilization significantly affected aggregate distribution,but not aggregate stability as characterized by mean weight diameter or geometric mean diameter.Long-term application of organic manure increased physical protection of organic carbon within macro-aggregates relative to chemical fertilizers,especially the high amount of organic fertilizer(M2),which can significantly improve the particulate organic carbon in micro aggregates within macro-aggregates(iPOM),thus increased the stability of organic carbon in the loess soil.