Soil Carbon Sequestration And Its Driving Factors Under Different Fertilization In Arable Land Of China

Soil organic carbon（SOC）and its fractions play key roles in maintaining and enhancing crop yield and improving soil quality.The SOC is not a homogeneous pool but a dynamic substance of various fractions characterized by different physical and chemical properties,decomposition rates and turnover times.How the processes and mechanisms of carbon（C）sequestration and the characteristics of different C fractions under different fertilization treatments is still unclear.We conducted a meta-analysis to address the effects of various fertilization practices on SOC and its fractions changes in China’s arable topsoil.Furthermore,we determined the effects of long-term NPK and NPKM fertilization on the protection mechanisms to sequester C based on 15 long-term experiments.The main findings were as follows:（1）We conducted a meta-analysis to address the effects of various fertilization practices on SOC changes in China’s arable topsoil.Compared to no fertilizers（CK）,on average,manure had C-retention coefficients of 31%±12%（95%Confidence Interval,CI）and 18%±2%for the experimental duration of≤10 years and>10 years,respectively.When compared to chemical fertilizers（NPK）,manure had C-retention coefficients of 29%±13%and 9%±3%for the experimental duration of≤10 years and>10years,respectively.In addition,compared to CK and NPK,application of manure increased SOC content by 0.23-0.26 and 0.18-0.19 g kg^-1 yr^-1,respectively.（2）We analysed the results of long-term field trials in Chinese croplands to determine the effects of fertilization strategies on SOC stock.The final SOC stock increased by 24～68%and 24～74%under NPKM and M,respectively.And the SOC stock under NPKM in Northeast and Northwest China were significantly higher than those under other treatments.Among the selected variables initial SOC stock was the most important in accounting for differences in SOC stock change rates（SOCr）,followed by soil bulk density,soil total nitrogen content,soil p H,mean annual temperature and precipitation.Fertilization strategy in different regions:it is necessary to increase the livestock manure application in NEC;the regular use of manure with chemical fertilizers is essential for the long-term SOC increase in NWC;in NC,however,with a relatively low SOC state,soils have a greater potential to sequester C,so the M with more C input also served as a pathway for substantial soil C sequestration;moderate manure application is a conducive practice for the SC.（3）We performed a meta-analysis to quantify the effect of fertilization on SOC fractions and investigated effects of climate,managements,soil properties and C inputs in China’s croplands.Manure application can be an effective way for sequestering C in each fraction to restore SOC.Fertilizers applied to soils resulted in significant positive changes in SOC and its fractions with the exception of minerals-associated organic carbon（MOC）,which did not change significantly under NPK relative to CK.NPKM dramatically increased the coarse particulate OC（cf POC,115%）,free particulate OC（ff POC,85%）,intra-microaggregate particulate OC（i POC,121%）and MOC（26%）.The cf POC and i POC are the main SOC fractions that affect SOC changes after fertilization.（4）We determined the effects of long-term NPK and NPKM fertilization on the protection mechanisms to sequester C based on 15 long-term experiments across China.The c POC and i POC were greater in the NPK as compared to CK.And NPKM significantly increased physically-protected C fractions.NPKM mainly increased the coarse particulate OC in subtropical humid SC area and the warm temperate semi-arid NWC area,and the increase of i POC was greater in mid-temperate semi-humid NEC area and warm temperate semi-humid NC area.The main protection mechanisms of SOC under different fertilization treatments:the main protection mechanisms of SOC in SC are unprotected and physical protection;the chemical and biochemical protection are in NEC and NC.The unprotected C fracions are mainly affected by C input,initial SOC and the soil total nitrogen content;while the chemically and biochemically protected C fractions are mainly affected by the soil chemical properties and soil clay particles content.A systematic study on the characteristics and driving factors of SOC sequestration and its stabilization mechanism in typical croplands in China.Identification of the dynamics of SOC fractions and its protection mechanisms under different long-term fertilization strategies will provide a scientific basis for SOC improvements and predicting the evolution of SOC in croplands.