Potential of Crop Residue and Fertilizer on Enrichment of Carbon Pools in Upland Soils of Subtropical India

In the investigation, the effect of variable crop residues and inorganic fertilizers on soil organic carbon (SOC) dynamics and its management indices was assessed in upland rice–lentil system. Treatments comprised of 4 levels of residue incorporation [residue removal, only rice residue (R), only lentil residue (L) and both rice + lentil (RL) residue] and 3 levels of fertilizer rate in lentil crop (0, 50, 100 % of RDF) fitted in split-plot design. After 7 years of continuous cropping, residue incorporation significantly ( P ≤ 0.05) increased the very labile (C frac 1 ), labile (C frac 2 ) and less labile (C frac 3 ) fractions of the total organic carbon (TOC) over residue removal, and the quantitative increase in C-fractions with residue incorporation followed the order C frac 2 > C frac 3 > C frac 1 > C frac 4 . However, the enrichment in different C-fractions and TOC was almost similar to the incorporation of either rice (R) or lentil (L) residue. Likewise, incorporation of both crop residues (RL) marginally increased in TOC and its fractions over single crop residue (R or L), but failed to bring significant changes, which indicates lower C-stabilization rate of additional crop residues. Substantial depletion in all the C-fractions was observed with zero fertilization in rabi season lentil crop and greatly restricted the buildup of C frac 1 . The quality indicators like lability index and carbon management index were improved with residue incorporation and effect restricted to surface depth (0–0.20 m) only. Thus, the findings suggest incorporation of minimum one crop residue, and optimal recommended fertilization in rabi crop would be helpful in economically managing the SOC in rice–lentil rotation of subtropical India.