Soil carbon sequestration rate, microbial biomass and mineralizable carbon and their interrelationship with system productivity under different cropping systems in an Inceptisol

Predominant crops under intensive cropping system grown either solely or in rotation with other crops tends to deplete soil nutrients necessary to boost soil productivity in Telangana state. As these crops are exhaustive, non-leguminous in nature and may lead to fast soil degradation. Therefore, a major agricultural research priority is needed to quantify soil microbial biomass carbon (SMBC) and soil mineralizable carbon (SMC) and sustain soil and crop productivity through Carbon Sequestration Rate (CSR) by including legume component in the cropping systems (CSs). The present study was undertaken to investigate the effect of CSs on CSR, SMBC and SMC in the ongoing long-term field trial. This field investigation was initiated during 2017 and undertaken in 2019-2020 at an experimental farm of College of Agriculture, Rajendranagar, Hyderabad, India. The results indicated the improvement in soil organic carbon (SOC) over the initial status due to the effect of efficient CSs. Significantly higher build-up of SOC was noted in the cropping sequence viz., CS₅: Maize + Pigeon pea (1:3) (1.25 Mg ha^-1) and CS₄: Pigeon pea + Greengram (1:3) - Sesame (1.22 Mg ha^-1). During the study, it was also observed that in one of the CSs i.e., CS₁₀: Bhendi - Marigold - Beetroot (6.77 Mg ha^-1) and CS1: Rice - maize (7.24 Mg ha^-1) showed the negative impact on the level of SOC stock fell below the initial value (7.53 Mg ha^-1) after third year of trial. Higher SMBC (240.62 mg kg^-1) and SMC (42.53 mg CO₂- C kg^-1) were pronounced under CS₄ and CS₃, followed by other legume-based cropping systems. However, the higher CSR was recorded in CS₅ (0.42 Mg ha^-1 yr^-1) and CS₄ (0.41 Mg ha^-1 yr^-1). Significantly highest system equivalent yield (40818 kg ha^-1) was under CS₁₀ and Pearson correlation (-0.755*) and 0.704* was significantly negative for CSR and positive for SMC. The salient findings of this study showed that CSs which included legumes sequestered more carbon and enhanced SMBC and SMC.