Soil Carbon Sequestration and Agronomic Productivity as Influenced by the Long-Term Organic and Inorganic Fertilisation Under the Upland Rice–Wheat System in Vertisols of Central India

Storage of anthropogenic carbon dioxide (CO₂) emissions in the soil profile is a current global challenge. Despite greater attention to research investigating the buildup of soil organic carbon (SOC) in the surface soil layer (0‒0.2 m), information on C sequestration rates in sub-soil layers (0‒1.0 m) is scanty in tropical upland crop production systems. We investigated the relationship of inputs of biomass C and C sequestration rates with the sustainability yield index (SYI) of the upland rice-based system in Vertisols of Central India. A randomised block design (RBD) was followed with five treatments viz., T1 = control; T2 = 100% recommended dose of nitrogen (RDN) (fertiliser) (40 kg N each for rice and wheat); T3 = 100% RDN (compost @ 8 Mg ha⁻¹); T4 = 50% RDN (fertiliser) + 50% RDN (compost); T5 = 50% RDN (fertiliser) + 50% RDN (compost) + Azotobacter (2 kg ha⁻¹). Changes in soil C stock under each treatment were measured for five depths (0–0.2, 0.2–0.4, 0.4–0.6, 0.6–0.8 and 0.8–1.0 m). Results of long-term (1998–2011) experiments highlighted that the total system productivity could be improved by regular inputs of compost. Maximum crop yields of rice and wheat (1829 and 2066 kg ha⁻¹, respectively) were obtained when 100% N was supplied through compost. However, the sustainability of the rice–wheat cropping system was improved with integrated nutrient management (INM) (T4). Mean SOC concentration increased from 4.50 to 6.03 g kg⁻¹ over control, and 19.2 Mg C ha⁻¹ was sequestered out of the cumulative total C input of 46.80 Mg C ha⁻¹ in the organic treatment (T3). A strong correlation (R² ≥ 0.96, P < 0.05) was found between total C inputs and profile C content, stock, and sequestration rate. The soil C sequestration efficiency was 67.9% for the rice–wheat cropping system. A critical C input of 1.30 Mg C ha⁻¹ yr⁻¹ was needed to maintain the SOC at the antecedent level for Vertisols. Thus, the combined application of organic amendments with fertilisers is paramount to sustain the productivity of the upland rice–wheat system and enhance SOC sequestration rates in sub-soil layers in Vertisols in sub-humid tropics.

Graphical Abstract