Appraisal of Nutrient Index to Assess Soil Fertility of Farming Lands : Spatial distribution of Macronutrients in soils

Soil samples collected from four river basins in Karnataka were characterized for different physical and chemical parameters namely pH, EC, Organic carbon, Exchangeable cations (Ca2+, Mg2+, Na+, K+), Available nutrients (N,P,K), Cation exchange capacity, percent base saturation, SAR & ESP. Soil fertility evaluated by calculating Nutrient Index using OC and Available NPK values indicated that the soils of SLIS, SRLIS, Bellary nala and Varahi river basins respectively fall under high-low-low-low (HLLL), medium-low-low-medium (MLLM), high-medium-high-medium (HMHM) & low-low-low-low (LLLL) class. Applying organic wastes as a source of nutrient to the agricultural lands having low to medium %OC and Available nitrogen is required. Soils with low to medium phosphorus could be supplemented by applying phosphorous rich fertilizers as required by a specific crop. Soil samples with deficient and doubtful supply of potassium can be enriched with garden compost holding 0.48% K2O or vermicompost holding ~0.7% K2O. Estimation of CEC & base saturation help to maintain adequate cationic nutrients pool for plant uptake with less leaching losses.