Abstract: We explored the effects of different organic compounds on soil organic carbon active components under the condition of reduced fertilizer application in purple soil in Sichuan, under purple potato and Solanum tuberdsm rotation system. There were seven treatments, including no fertilization (CK), conventional fertilizer (CF), conventional fertilizer with straw (CFS), reduced 50% fertilizer with microbial organic fertilizer (RFM), reduced 50% fertilizer with earthworm biological compound organic fertilizer (RFV), reduced 50% fertilizer with straw and microbial organic fertilizer (RFSM), reduced 50% fertilizer with straw and earthworm biological compound fertilizer (RFSV). The results showed that the application of organic materials did not affect soil total organic carbon content, but significantly increased microbial biomass carbon (MBC) and the content of labile organic carbon (LOC) by 10.6%-42.6%. The results of three-dimensional fluorescence analysis of soil dissolved organic carbon (DOC) showed that humic acid and furitic acid were the main components of DOC in purple soil. Under the treatments of RFSM and RFSV, the contents of humic acid and furitic acid increased, while tryptophan, tyrosine and soluble microbial metabolites decreased. The three-dimensional fluorescence index increased, indicating that DOC was mainly derived from the metabolic activities of microorganisms. In conclusion, organic fertilizer addition under reduced chemical fertilizer application could increase MBC and LOC content and change the component structure of DOC.

Key words: organic fertilizer, organic carbon, active component, three-dimensional fluorescence.