Soil Carbon Fractions at Different Soil Depths as Influenced by Land use Practices under Cropping Systems in a Vertisol

The experimental field study was conducted at Borlaug Institute for South Asia (BISA) Research Farm, Lakhanwada, Jabalpur, Madhya Pradesh, India to evaluate the soil carbon fractions (very labile, labile, less labile and non-labile or recalcitrant carbon) in different land use practices with soil depths under cropping systems in Vertisols after harvest of Kharif and Rabi season crops of year 2015-16 and 2016-17. The experiment was conducted under Split plot design considering land use practices as main plot treatments [L1: Uncultivated, L2: rice-wheat system with conventional agriculture (CT), L3: rice-wheat system with conservation agriculture (CA), L4: soybean-wheat system with CT, L5: soybean-wheat system with CA, L6: maize-wheat system with CT and L7: maize-wheat system with CA] and depth (0-5 cm, 5-15 cm and 15-30 cm) as sub-plot treatments replicated thrice. Very labile carbon fraction was obtained highest in L3 (rice-wheat system with CA) and lowest under L6 (maize -wheat system with CT) treatment after harvest of Kharif and Rabi season crops during 2015-16 and 2016-17and it was significantly higher at 0-5 cm soil depth than those in 5-15 cm and 15-30 cm soil depths. Similar trends were also obtained in case of labile, less labile and non-labile fraction of carbon i.e. the applied land use practices had significant effect on all the carbon fractions under study and found to be maximum under L3 (R-W system with CA) and minimum in L6: (M-W system with CT) treatment after harvest of both the season crops during both years of experiment. Whereas, the interaction effect of land use practices and soil depths on the carbon fractions was found statistically non-significant during both the seasons and years.

Short-Term Carbon Sequestration and Changes of Soil Organic Carbon Pools in Rice under Integrated Nutrient Management in India

While the capability of integrated nutrient management (INM) in rice systems has been adequately studied, little is known about the related short-term carbon sequestration and changes in soil carbon fractions. Our study examined the responses of organic carbon pools, carbon sequestration and rice yields after application of different organic manures combined with chemical fertilizers in a rice–rice (Oryza sativa L.) cropping system in the red and laterite agro-climatic zones of West Bengal, India. The treatments included non-fertilized control; rice straw (RS) + nitrogen, phosphorus and potassium fertilizer (NPK); Gliricidia (GL) + NPK; farmyard manure (FYM) + NPK; vermicompost (VC) + NPK; and NPK only. Rice straw + NPK treatment resulted in the highest total organic carbon and passive pool of carbon. Vermicompost + NPK treatment resulted in the highest oxidizable organic carbon (0.69%), dissolved organic carbon (0.007%) and microbial biomass carbon (0.01%), followed by FYM + NPK, GL + NPK and RS + NPK as compared to control. Rice straw + NPK sequestered the highest amount of carbon dioxide (CO2) as the total organic carbon (91.10 t ha−1) and passive pool of carbon (85.64 t ha−1), whereas VC + NPK resulted in the highest amount of CO2 (10.24 t ha−1) being sequestered as the active pool of carbon, followed by FYM + NPK (8.33 t ha−1) and GL + NPK (7.22 t ha−1). The application of both NPK only and VC + NPK treatments resulted in the highest grain yields over the three cropping seasons. In spite of high carbon sequestration being observed in more recalcitrant carbon pools, RS + NPK resulted in little increase (3.52 t ha−1) in rice yield over the short term. The results of this study suggest that the short-term changes of soil carbon fractions and carbon sequestration primarily depend on the type of organic manure used. Vermicompost, FYM and GL provide more labile carbon, which can improve rice yield over the short term. However, it is suggested to explore the dynamics of different carbon fractions, carbon sequestration in different pools and rice yields over longer periods of time.