Organic matter fractions and soil carbon sequestration after 15-years of integrated nutrient management and tillage systems in an annual double cropping system in northern India

Abstract

Labile soil organic carbon pools are valuable indicators of soil quality, early changes in soil total organic carbon (TOC) stocks, and (hence) changes in soil carbon sequestration pools and dynamics induced by changes in soil tillage and nutrient management practices. To improve the soil carbon sequestration in northern India, we have examined effects of tillage, crop residues and nutrient management treatments applied in a 15-year experiment on TOC and the following fractions: soil organic carbon (SOC), particulate organic carbon (POC), total nitrogen (TN), water soluble carbon (WSC), light fraction organic carbon (LFOC), dissolved organic carbon (DOC) microbial biomass carbon and (MBC). The tillage crop residue practices were ZT without residue (T1), ZT with 4 tha-1 residue retained (T2), ZT with 6 tha-1 residue retained (T3), PRB without residue (T4), PRB with 4 tha-1 residue retained (T5), PRB with 6 tha-1 residue retained (T6), and conventional tillage (T7) was combined with the following nutrient management treatments: control (no manure and fertilizer) (F1), 100% RDN as CF (F2), 75% RDN as CF+25% RDN as FYM (F3), 75% RDN as CF+25% RDN as GM/SPM (F4), 50% RDN as CF+50% RDN as FYM (F5), 50% RDN as CF+50% RDN as GM/SPM (F6) and1/3rd N as CF+1/3rd N as FYM+1/3rd N as GM/SPM (F7). After 15 years, T3 treatment resulted in significantly increased 66.1%, 63.9%, 57.9%, 50.9%, 39.4%, 38.3%, 37.3% and 32% LFOC, TOC, SOC, PON, TN, LFON, DOC and POC, over T7 treatment and WSC 39.6% in surface soil and 37.4% in subsurface soil. Out of the four C fractions, LFOC and KMnO4 C were the most sensitive indicators of changes in TOC induced by the soil tillage and nutrient management practices. Under RWCS, TOC contents were similar in F6, F7 and F3 plots, and significantly higher than those in F1 plots (by 50.4% 48.3%, and 43.3% respectively). Manure addition further enhanced TOC contents, which were highest following the F5 treatment (21.37 gkg−1). LFOC were also significantly higher following the treatments including organic amendment than following applications solely of chemical fertilizers, except that the F5, F6 and F7 treatments resulted in similar LFOC contents. Application solely of chemical fertilizers had no significant effects on LFOC and KMnO4C fractions compared with unfertilized control plots. Nevertheless, application of F5 or F6 significantly increased contents of POC and MBC relative to F1 (by 49.6%and 40.9% or70.2% and 63.4%, respectively). These results demonstrated that conservation agriculture that integrates application of nutrient management, tillage and crop residue is crucial for improving soil health and sustainability of farming systems in northern India.