Author(s):

RK Naresh, Arvind Kumar, S Bhaskar, SS Dhaliwal, Vivek, Satendra Kumar, Sunil Kumar and RK Gupta

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) and1/3^rd N as CF+1/3^rd N as FYM+1/3^rd 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.

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