Soil organic carbon stocks and fractions in different orchards of eastern plateau and hill region of India

Soil organic carbon (SOC) plays an important role in soil fertility and productivity. It occurs in soil in labile and non-labile forms that help in maintaining the soil health. An investigation was undertaken to evaluate the dynamics of total soil organic carbon (Ctot), oxidisable organic carbon (Coc), very labile carbon (C frac1), labile carbon (C frac2), less labile carbon (C frac3), non-labile carbon (C frac4), microbial biomass carbon (Cmic) and SOC sequestration in a 6-year-old fruit orchards. The mango, guava and litchi orchards caused an enrichment of Ctot by 17.2, 12.6 and 11 %, respectively, over the control. The mango orchard registered highest significant increase of 20.7, 13.5 and 17.4 % in C frac1, C frac2 and C frac4, respectively, over control. There is greater accumulation of all the C fractions in the surface soil (0–0.30 m). The maximum total active carbon pool was 36.2 Mg C ha−1 in mango orchard and resulted in 1.2 times higher than control. The passive pool of carbon constituted about 42.4 % of Ctot and registered maximum in the mango orchard. The maximum Cmic was 370 mg C kg−1 in guava orchard and constituted 4.2 % of Ctot. The carbon management index registered 1.2 (mango orchard)- and 1.13 (guava and litchi orchard)-fold increase over control. The mango orchard registered highest carbon build rate of 1.53 Mg C ha−1 year−1 and resulted in 17.3 % carbon build-up over control. Among the carbon fractions, C frac1 was highly correlated (r = 0.567**) with Cmic.