Nutrient uptake and soil fertility status after harvest of Bt cotton as influenced by graded levels of NPK fertilizers in Alfisol

Field studies were conducted at farmer’s fields in Jodalli (Kalghatgi taluk) and Pale (Hubballi taluk) villages in 2012-13 and 2013-14, respectively to investigate the effect of NPK fertilizers on uptake of nutrients by Bt cotton and soil fertility status at harvest in Alfisol. Among the different treatment combinations, the application of 150:50:75 kg N:P2O5:K2O ha-1 (N3P1K2) recorded significantly (P=0.05) higher nitrogen (132.63 kg ha-1), phosphorus (31.26 kg ha-1) and potassium (128.94 kg ha-1) uptake by cotton. The interaction effect with respect to total micronutrients (Zn, Fe, Mn and Cu) uptake remained non significant at all the growth stages. Graded levels of fertilizers failed to exert significant impact on pH and electrical conductivity, soil organic carbon and available micronutrients during both the years of experimentation. The application of 100:50:50 kgN:P2O5:K2O ha-1 (N1P1K1) recorded significantly (P=0.05) highest available nitrogen (150.39 kg ha-1), available phosphorus (37.98 kg ha-1) and available potassium (230.99 kg ha-1) compared to rest of the treatments. The lowest available nitrogen (134.92 kg ha-1), available phosphorus (31.65 kg ha-1) and available potassium (217.63 kg ha-1) were recorded in treatment receiving 150:50:75 kg N:P2O5:K2O ha-1 (N3P1K2)