Abstract:

【Objective】 Based on 3 long-term experiments, temporal and spatial responses of total soil organic carbon (TOC) and labile organic carbon (LOC) in red soil, black soil and grey-desert soil to various long-term fertilizations were discussed.【Method】 Fractionation method of soil organic carbon was applied to determine the contents of LOC and the percentage of LOC to TOC in black soil, grey-desert soil and red soil. 【Result】 Results showed that the content of TOC and LOC and the percentage of LOC to TOC under 16 years of non-fertilization (CK) in grey-desert soil decreased significantly by 11.7%, 34.9% and 5.4 percentage points, respectively. After long-term application of chemical nitrogen fertilizer (N), the content of TOC of the 3 soils kept no significant change throughout the studied period. However, the percentage of LOC to TOC for the 3 soils all decreased significantly. It decreased by 9.5 percentage points in black soil, which was the most of the 3 studied soils. After 16 years application of NP and NPK, the percentage of LOC to TOC in black soil and grey-desert soil decreased significantly. While there was increasing trend for red soil. There was significant increase in the contents of TOC and LOC and the percentage of LOC to TOC under long-term application of chemical fertilizers combinated with manure (NPKM、1.5 NPKM). After long-term application of NPKM, the contents of TOC, LOC and the percentage of LOC to TOC in red soil increased by 80.6%, 146.2% and 7.5 percentage points, respectively, which was the most. For grey-desert soil it was 64.4%, 138.0% and 5.0 percentage points, respectively. For long-term application of NPK with straw return (NPKS), the contents of TOC, LOC and the percentage of LOC to TOC in red soil increased by 21.6%, 59.0% and 7.5 percentage points. However, it was stable in black soil and grey-desert soil. 【Conclusion】 The percentage of LOC to TOC response sensitively to long-term fertilization and could be one of the indicators for the quality of soil organic carbon. Long-term non-fertilization and only chemical nitrogen fertilizers lead to decrease in the contents of total soil organic carbon and the percentage of LOC to TOC in most cases. Long-term application of NPKM could maintain and improve quality and quantity of soil organic carbon. The effect of long-term application of NPKM was better than that of NPKS, and they were both better than that of long-term application of NPK.

Key words: long-term fertilization, organic carbon, labile organic carbon, black soil, grey-desert soil, red soil