Characterization of Bt Cotton Growing Soils Producing Varying Cotton Yields in Dharwad and Haveri Districts of North Karnataka, India

Bt cotton is being cultivated on a wide range of soils in northern transitional zone of Dharwad and Haveri districts in north Karnataka. A field survey was conducted during kharif 2021-22 to study the physico-chemical properties and nutrients status of soil and Bt cotton productivity. A total of 153 locations were selected in Dharwad and Haveri districts. Surface soil samples were collected at fifty per cent flowering stage and kapas yield was recorded at first and second picking stages. In the study area, kapas yield ranged from 3.59 to 25.85 q ha-1 with a mean value of 15.95 q ha-1. Bulk density, soil porosity, maximum water holding capacity and moisture content at field capacity ranged from 1.12 to 1.70 Mg m-3, 35.85 to 57.74%, 34.08 to 76.27% and 13.63 to 45.76%, respectively. Soils were near neutral to slightly alkaline in reaction (6.60 to 8.80), non-saline (0.15 to 0.82 dS m-1), slightly to moderately high in free lime content (4.10 to 18.40%) and low to high in soil organic carbon (1.50 to 12.60 g kg-1) content. Available nitrogen, phosphorus (P2O5), potassium (K2O) and sulphur contents in soils of cotton fields ranged from 113.06 to 562.82, 10.50 to 89.56, 110.16 to 497.28 kg ha-1 and 5.06 to 25.67 mg kg-1, respectively. Similarly exchangeable calcium and magnesium contents in soils ranged from 10.10 to 35.24 and 2.98 to 17.01 cmol (p+) kg-1, respectively. DTPA extractable iron and zinc contents and hot water soluble boron content in soils ranged from 1.86 to 9.51, 0.20 to 1.10 and 0.10 to 0.75 mg kg-1, respectively. Nutrient indices showed that soils of the study area were low in available nitrogen, medium in available phosphorus, potassium and sulphur contents. Iron, zinc and available boron contents were deficient in soils.