Effects of long-term fertilization on labile organic matter and carbon management index(CMI) of the typical soils of China

Effects of long-term fertilization on labile organic matter and carbon management index(CMI) in red soil,grey-desert soil,loessial soil,fluvo-aquic soil,cinnamon soil and black soil were studied in order to assess soil quality.Soil labile organic matter was measured by oxidation of KMnO4 with three fractionations,namely,high labile organic matter(measured by oxidation of 33(mmol/L) KMnO4),middle labile organic matter(measured by oxidation of 167(mmol/L) KMnO4),and low labile organic matter(measured by oxidation of 333(mmol/L) KMnO4).The results indicated that after 10 years long term cultivation with no fertilization(CK),the labile organic matter in soils diminished and CMI decreased by 11.163.6 in different soils,among which loess soil and cinnamon soil decreased the most and black soil the least.Soil labile organic matter also decreased after chemical fertilizer was applied,among which the decrease in fluvo-aquic soil was the most under single application of nitrogen(N),accounting for 31.3%,while it decreased most in red soil under mixed-application of chemical fertilizers(NPK). Soil total organic matter and labile organic matter content in these treatments of fertilizer applied were higher than that in CK and original soils,and there was significant increase in soil(labile) organic matter and CMI under application of manure or co-application of manure and chemical fertilizers,with the most increase of CMI in red soil(91.4) and the least increase in fluvo-aquic soil(4.6).The change amplitudes of soil labile organic matter content and CMI were lager than that of soil total organic matter,with the largest change for CMI,which suggested that CMI was the best index to assess influence of fertilization and cultivation on soil quality.The fractionation of soil labile organic matter showed that high labile organic matter in red soil,high and middle labile organic matter in loess soil and grey-desert soil,and middle labile organic matter in fluvo-aquic soil were main parts among labile organic matter.There were apparent effects of long-term fertilization on labile organic matter fractionations in red soil and grey-desert soil,while its effects were less in loess soil and fluvo-aquic soil.