Assessment of Nutrient Contribution towards Yield of Bt Cotton through Omission Plot Techniques in Karnataka

The current project was aimed at assessing the yield responses to applied nutrients and understanding the extent of spatial and temporal variability of nutrient responses across the cotton-growing soils of northern Karnataka. On-farm nutrient omission plot experiments were conducted in farmers’ fields at 17 locations in the intensive cotton-growing districts of Gadag, Belgaum and Dharwad, varying in soil types from red, laterite to medium black and deep black soils. Cotton was grown under both rainfed as well as with supplemental irrigation. The experiments consisted of four treatments including: ample NPK (180-70-80 kg N-P₂O₅-K₂O kg/ha), N Omission, P Omission, and K Omission at each location.

The results observed during 2013-14 revealed that the seed cotton yield (SCY) in the ample NPK plots averaged 3,171 kg/ha and ranged from 2,420 to 3,640 kg/ha. Omission of N, P and K resulted in 37, 13 and 10% reduction in SCY as compared to ample NPK application (3,171 kg/ha). Yield response to application of N, P and K averaged 1,175, 310 and 421 kg/ha and ranged from 870-1,470, 70-620 and 170-740 kg/ha, respectively. The net returns were reduced by 59%, 12% and 18% with N, P and K omission as compared to the ample NPK application. With the ample NPK treatment, the superior yield characteristics such as plant height (105 cm), number of bolls per plant (34), boll weight (6.6 g), dry matter yield (77) and seed cotton yield (124 g/plant) resulted in significantly higher yield over the respective nutrient omission treatments. Uptake of N (61 kg/ha), P (16 kg/ha) and K (60 kg/ha) with the ample NPK application was also higher than the average uptake of N (45 kg/ha), P (28 kg/ha) and K (50 kg/ha) observed with omission of N, P and K, respectively. Post-harvest soil available nutrient status revealed that available N, P and K in the ample NPK treatment was 254, 42 and 529 kg/ha, which was reduced significantly by 8% (N), 15% (P) and 1% (K) with nutrient omission, giving an indication about the indigenous nutrient supplying capacity of the soil.

The information generated from this study will be utilized for refining the Nutrient Expert^(R) decision support tool for cotton and will help in providing individual field-specific fertilizer recommendations for improving the productivity and profitability of farmers growing cotton.