Yield maximization in cotton through targeted yield approach and omission plot techniques in Vertisols of Karnataka

A replicated on-station study on cotton was undertaken at the research farm of the University of Agricultural Sciences in Dharwad (northern Karnataka) during the monsoon season of 2016. The objective of the study was to assess the contribution of nitrogen (N), phosphorus (P), and potassium (K) towards the yield of Bt cotton, determine the nutrient uptake, and to work out the extent of economic loss due to the omission of major nutrients as compared to the fully fertilized plot. The study consisted of four treatments: (T₁) ample NPK (180-70-80 kg N-P-K/ha), (T₂) N Omission, (T₃) P Omission, and (T₄) K Omission. Additional micro and secondary nutrients were applied based on the soil test results.

The study indicated that the application of ample NPK produced a large number of bolls/plant (28) and high seed cotton yield (SCY) (2,820 kg/ha). Nitrogen (N) omission resulted in the lowest SCY (1,460 kg/ha), followed by K omission (2,450 kg/ha) and P omission (2,550 kg/ha). The omission of N, P, and K resulted in 48, 9, and 13% reduction in SCY as compared to the application of ample NPK. There was a significant reduction in net returns and benefits:cost ratio under N omission (Rs.6,939/ha and 1.1), followed by K omission (Rs.42,749/ha and 1.8) and P omission (Rs.47,599/ha and 1.9). The extent of reduction in net returns under N, P, and K omission treatments were 88, 16, and 24%, respectively compared to the ample NPK treatment. Application of ample NPK resulted in higher N, P, and K uptake as compared to omission of N, which had the lowest uptake of these nutrients. Similarly, omission of P and K recorded the lowest P and K uptake, respectively. Fiber quality parameter like fiber strength and fiber length were reduced in K omission plots compared to ample NPK. Fiber fineness was reduced in the nutrient omission treatments compared to the application of ample NPK, as the micronnaire value was higher in nutrient omission treatments against the application of ample NPK. Ginning out turn (GOT) was more in NPK applied plots, and omission of N, P, and K recorded lower GOT.

The information generated in this study will be utilized for developing the Nutrient Expert® decision support tool for cotton, and help in providing field-specific fertilizer recommendations for improving the productivity and profitability of farmers growing transgenic cotton.