GIS-based soil fertility assessment of a micro-watershed of semi-arid tropics in southern India

Available macronutrient status in the soil of Chotanahalli micro-watershed (468 ha) in Kunigal Taluk, Tumkur district was studied with the aid of GIS. Forty three surface soil samples at 320 m grid were collected from Chotanahalli micro-watershed and assessed for the soil organic carbon, available nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Results revealed that the ranges of SOC, available N, P and K were 2.1 to 7.5 g kg-1, 282.2 to 526.8 kg N ha-1, 8.0 to 67.6 kg P2O5 ha-1 and 124.3 to 338.5 kg K2O ha-1, respectively. Spatial interpolation revealed that majority (321 ha) of the watershed was low in SOC, whereas the whole watershed was medium in available N, P and K. In case of secondary nutrients, available S was found to be medium in majority (423.4 ha) of the area, whereas, exchangeable Ca and Mg were found sufficient in the whole watershed. The Nutrient Index values indicated that the micro-watershed was under “medium” category for available nitrogen, phosphorus, potassium and sulphur, whereas, it fell under “low” category with respect to organic carbon. Measures to improve the status of SOC should be taken up in the study area for sustainable production of crop.