Soil Carbon Sequestration, Nitrogen Pools and Greenhouse Gas Emission Under Different Cropping Systems in Long-term Conservation Agriculture Practices

Abstract

In the decades following India's independence, the Green Revolution played a pivotal role in transforming the agricultural landscape, significantly boosting food grain production, particularly wheat and rice. However, this intensification has led to substantial environmental challenges, including soil degradation, groundwater depletion, and increased greenhouse gas emissions. In response, this research investigates the potential of conservation agriculture (CA) and diversified cropping systems to address these issues. CA, with its emphasis on minimal soil disturbance, proper soil cover, and crop diversification, holds significant potential to reduce production costs, provide essential ecological services for soil and environmental health, and lower the carbon footprint and greenhouse gas emissions. This study explores the potential of CA practices to improve soil carbon sequestration, optimize nitrogen pools, and mitigate greenhouse gas emissions. Keeping these points in view soil samples from 0-60 cm (at 15 cm interval) were collected after the harvest of Rabi wheat 2023 from an ongoing long-term CA based experiment comprised of four cropping systems i.e. rice (Oryza sativa L)-wheat (Triticum aestivum) (R-W), rice-wheat-greengram (Vigna radiata) (R-W-GG), maize (Zea mays)-mustard (Brassica juncea)-greengram (M-M-GG) and sugarcane (Saccharum officinarum)-ratoon-wheat (Sr-Rt-W) are being grown in CA and conventional tillage (CT) since July 2015 arranged in a factorial randomized block design (FRBD) with three replicates. The collected soil samples were analyzed for different carbon fractions, C stock, total soil organic carbon and nitrogen pools. Additionally, gas samples were collected to assess temporal variations in greenhouse gas emissions using the closed chamber method. Results showed that CA based management practices in R-W, R-W-GG, M-M-GG and Sr+GG-Rt+GG-W cropping system recorded 28.5, 52.8, 69.4 and 39.4% higher labile carbon (CVL and CL) over the R-W (CP) system. Similarly, 10, 44.5, 63 and 37.5% increase in recalcitrant pools (CLL and CNL) in these cropping systems over the R-W (CP) system. Among the CA practices, M-M-GG (CA) system recorded 114.9, 110.5 and 112.6% higher C stock, total soil organic carbon and Walkley Black carbon as compared to R-W (CP). Similarly, M-M-GG (CA) system registered 30.58, 40.01, 28.86, 31.52 and 23.46% higher labile N, mineral N, microbial biomass N, potential mineralizable N and total N, respectively. Soil CH4 fluxes in the plots under CA based treatments ranged from 64.2 mg m-2 day-1 to 530.9 mg m-2 day-1 and 55.6 mg m-2 day-1 to 409.8 mg m-2 day-1 in R-W (CA) and R-W-GG (CA) during the rice growing season, respectively. Overall, CA based systems recorded 12.14 and 21.43% lower N2O emission in rice system over the business-as-usual treatment (R-W-CP) while the magnitude of reduction in N2O emission was 43.64 and 52.97% during wheat growing season. In conclusion, long term CA practice, particularly the M-M-GG system in Indo-Gangetic plain, significantly improves soil carbon and nitrogen levels while reducing greenhouse gas emissions over R-W (CP).