Soil Degradation Effect on Soil Productivity, Carbon Pools and Soil Enzyme Activity

Land degradation is one of the major causes of decline in soil productivity. However, the quantitative relationship between degradation and productivity is not fully understood in soils of India. Thus, an experiment was conducted under a range of native soil organic carbon (SOC) levels in two soil types (Inceptisol and Alfisol) of subtropical India. The SOC content under the treatments was 1.61%, 1.01% and 0.77% in Inceptisol and 0.36%, 0.25% and 0.21% in Alfisol under C₁ (undepleted soil), C₂ (low depletion) and C₃ (medium depletion) treatments respectively. Soybean was grown under each SOC level, with four management practices, viz. (1) control, (2) recommended dose of fertilizers (RDF) + 10 Mg farmyard manure (FYM) ha^-1, (3) 20 Mg FYM ha^-1 and (4) 150% RDF, in three replicates in a factorial completely randomized design. Results indicated significant and positive effect of both SOC and management treatment on plant biomass yield, labile (KMnO₄ oxidizable) carbon, soil microbial biomass carbon (SMBC), dehydrogenase activity, soil bulk density (BD) and penetration resistance (PR). The plant biomass reduced by 45% and 29% under C₃ (compared to C₁) in Inceptisol and Alfisol respectively. The effect of SOC depletion was conspicuous in Inceptisol. The labile C reduced by 47% and 16% under C₃ in Inceptisol and Alfisol respectively. SMBC showed a corresponding decrease of 33% and 29%. The soil physical properties, viz. BD and PR showed conspicuous effect of SOC depletion. PR increased by 324% and 75% for Inceptisol and Alfisol respectively.