Soil Fertility Evaluation in Rainfed Regions of Different Agro-Climatic Zones of Karnataka, India

The strategy for increasing crop production is either based on bringing new lands under cultivation or through intensive cultivation with improved management practices. Nevertheless, both the strategies require constant monitoring of soil fertility status to avoid nutrient deficiency that is one of the major constraints for crop production and it is a decisive tool for farmers and policy planners in soil nutrient management. The integrated watershed management programme called SUJALA by the watershed department, Karnataka, facilitated to diagnose the soil nutrient status in rainfed areas of Karnataka by collecting soil samples at grid interval from the farmer’s field. A total of 34,011 georeferenced composite samples (0–15 cm) were collected at a 325 × 325 m grid interval to analyse the fertility status of soils. The samples were aggregated under different agro-climatic zones of Karnataka to assess the soil fertility status under each zone. The results showed that per cent sample of low soil organic carbon (< 0.5%) was high in EDZ (61%) and low available P was high in NETZ (85%), NTZ (72%), NEDZ (55%) and NDZ (53%). The soil available potassium was medium to high category. Widespread deficiency of boron (49–68%) and zinc (61–89%) was noticed in all the agro-climatic zones, whereas the per cent deficient of soil available Fe was high in NDZ (54%), NTZ (51%) and the deficient available sulphur was high in SDZ (57%), NEDZ (56%) and NDZ (52%). The principal component analysis revealed that organic carbon has a strong influence on the availability of Cu and Mn, whereas available P, K, Fe and Zn were strongly influenced by soil pH. Soil EC has a significant effect on the availability of sulphur and boron. Hence, soil fertility management is apparent in rainfed regions to improve and sustain crop production against widespread multi-nutrient deficiency across the agro-climatic zones of Karnataka.