Effect of long-term fertilization on content of total and particulate organic carbon and their depth distribution of a paddy soil: An example of huangnitu from the Tai Lake region,China

Total soil organic carbon(TOC) is a soil carbon storage index and particulate organic carbon(POC) is generally considered as a labile organic carbon pool in response to environmental and management changes.In this paper,variations both of TOC and POC with soil depth under long-term different fertilization practices were studied in a paddy soil.Totally 4 treatments including chemical fertilizer with straw return,chemical fertilizer plus pig manure,chemical fertilizers only and no fertilizer application were set up in this study.The results were as follows: the depth distribution of both TOC and POC fitted best to power function equations.Fertilization significantly affected TOC and POC in topsoil,(among) which TOC and POC in the treatment of chemical fertilizer plus pig manure was the highest.However,POC contents under no fertilization were still higher than both chemical fertilization and chemical plus straw return,and no liner relation was observed between POC content in ploughing layer and mean crop yield.This indicated that POC contents did not mainly stem from the input of crop biomass.This was further supported by the fact that POC content was not in significant correlation with the average yield of the different plots.Meanwhile,there was no significant correlation between POC and the content of coarse particle size fractions,suggesting the properties and construction of POC under different fertilization differed in its ability to contribute to soil aggregation.Thus,the different fertilization practices tended to(affect) not the depth distribution of TOC and POC but the content and proportion of POC in topsoil.The variation of composition and binding ability of POC under these different treatments needs further study.