Soil Labile Organic Carbon Fractions and Carbon Management Index in Response to Different Fertilization under Organic Maize Farming System

Organic farming has been known to improve soil quality by enhancing soil organic carbon (SOC) contents. The labile organic carbon (LOC) pools and carbon management index (CMI) are commonly used as very sensitive indicators of changes in SOC and assessment of soil quality. This study was conducted to investigate the effect of organic farming practices on soil quality by LOC fractions and CMI analysis in a 6-year field experiment. Four treatments were included: compost (COM), green manure (GM), inorganic fertilizer (NPK), and no fertilization (NF). This study was designed to explore changes in SOC concentrations, soil labile organic C fractions (microbial biomass C (MBC), water and hot water-extractable C (WEC, HWEC), particulate organic C (POC), light fraction organic C (LFOC) and permanganate oxidizable C (POXC)) and CMI within the bulk soil under organic corn cultivation condition. Organic fertilization significantly increased SOC concentrations and stocks by 10 -55% compared to NPK and NF, especially, compost treatment. All labile carbon fractions were higher in COM and GM compared to NPK and NP, except MBC content. Among the LOC fractions, POC showed the highest proportion (32 -87%) on total SOC. The CMI varied from 0.87 to 2.77, organic fertilized treatments increased by 1.7 -3.2 times over NPK. These results showed that POC and POXC could be used as a rapid and informative indicator to assess soil quality and SOC changes. Hence, organic farming management could therefore contribute to improved nutrient cycling services and higher soil quality.