Soil carbon stock and its economic valuation in different agro-climatic zones for productivity enhancement in Karnataka

Soil Carbon (SC) storage is a key indicator of soil function used to monitor and predict crop response to management decisions. Under the SUJALA-3 Watershed Development project, a total of 202 soil series representing maj or pigeon pea growing soils were studied in seven agro-climatic zones of Karnataka. The organic and inorganic carbon stock status was estimated at different soil depths to arrive at the economic value and assessed its relation with crop production. The SOC and SIC stock was 23.8 and 11.2 t ha^-1 at 0-30 cm, 42.0 and 32.1 t ha^-1 at 30-100 cm and 66.9 and 42.8 t ha^-1 at 0-100 cm depth, respectively. The yield of pigeon pea was high (12.18 q ha^-1) under high OC status of clay textured soils followed by medium SOC (11.11q ha^-1) and low OC soils (11.52 q ha^-1) in NETZ region. Using the agglomeration method, five groups were derived to determine the soil organic carbon management clusters. The soil organic carbon deficit (t ha^-1) calculated to arrive investment requirement showed the order of cluster-4>cluster-3>cluster-1>cluster-5>cluster-2 and the investment required to bridge the gap was Rs. 30228, 26508, 26190, 22674 and 21990, respectively. As soil structure stability has an important role in carbon sequestration, the polynomial equation was constructed between soil carbon density and soil structural stability index, which yielded a threshold soil carbon stock value of 66.6 t ha^-1 to attain a stable soil structure index value of nine. The ANOVA analysis showed statistically significant differences in SOC stock between regions (p = 0.022) and soil subgroups (p = 0.001). The study concludes an average investment of Rs 25,000 /ha/yr for 20 yr is required for enhancing soil carbon status in Karnataka and to achieve the Pigeon pea potential yield of 20 q ha^-1