Soil organic carbon pools after seven years of manures and mineral fertilizers application in a rice-wheat rotation

Abstract

A long-term experiment under a rice-wheat system, which represents an alternate flooding (reducing) and upland (oxidation) conditions, was used to evaluate the effect of organic manures and mineral fertilization on various organic carbon pools in soil. Application of mineral fertilizers alone increased the dissolved organic carbon (DOC), microbial biomass carbon (MBC), light fraction carbon (LFC), and heavy fraction carbon (HFC) by a factor of 1.4–2.4 compared with control. On the other hand, application of farmyard manure, press mud and green manure along with mineral fertilizers enhanced DOC content by 73.0, 93.9, and 56.5%, respectively, over mineral fertilizer only (N150P75K75Zn25) treatment. The increments in MBC due to corresponding treatments over mineral fertilizers were 73.7, 79.6 and 30.2%, respectively. A maximum increase of 2.5- to 3.4-fold was observed in LFC due to combined application of organic manures and mineral fertilizers over control. Notably, the HFC constituted the major proportion (about 83.3%) of the total soil carbon. The increase in surface soil carbon accounted for 24.9, 28.3 and 7.0% of the carbon added through farmyard manure, press mud and green manure, respectively.