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

The current project was aimed at assessing the yield response of cotton to applications of N, P₂O₅, and K₂O and to determine 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 15 locations in the intensive cotton-growing districts of Belgaum and Dharwad, varying in soil types from red laterite to medium black, and deep black soils. The soils at the experimental sites were neutral to alkaline in reaction (pH 6.8 to 8.2), low in available N (240 kg/ha), medium in available P₂O₅ (38 kg/ha), and high in available K₂O (540 kg/ha). 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 2014-15 revealed that the seed cotton yield (SCY) in the ample NPK plots averaged 2,720 kg/ha and ranged from 2,250 to 3,210 kg/ha. Omission of N, P and K resulted in 30, 11, and 15% reduction in SCY as compared to ample NPK application. Yield response to application of N, P, and K averaged 830, 310, and 420 kg/ha and ranged from 295 to 1,300, 90 to 630, and 200 to 715 kg/ha, respectively. The data on nutrient uptake is currently being analyzed.

The information generated from this study will be utilized for refining the Nutrient Expert® 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.