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

The project was initiated to assess the yield responses to N, P and K fertilizer application in different Bt cotton growing farmer fields and also understand the extent of indigenous nutrient supplying capacity of soils. This information will help develop the QUEFTS for Bt cotton and will contribute to development of Nutrient Expert Cotton for South Asia.

IPNI-2013-IND-524

04 Apr 2014

2013 Annual Interpretive Summary


On-farm studies were initiated in farmer fields of northern Karnataka where transgenic cotton is grown. The objectives of this study were to assess the yield responses to applied nutrients and understand the extent of indigenous nutrient supplying capacity of soils. Experiments were conducted at 30 farms in six different districts (Dharwad, Gadag, Haveri, Belgaum, Bijapur, and Bagalkot) of northern Karnataka, with soil types varying from medium black to deep black. All the selected locations had rainfed ecology, with supplemental irrigation occurring during critical stages of crop growth as needed. The local farmers differed in the hybrid of transgenic cotton being grown. The pH of the experimental soils was alkaline (ranging from pH 7.6 to 8.9), with low to medium amounts of available N (168 to 290 kg/ha) and high available P and K contents. The experiment consisted of four treatments, viz., ample NPK treatment consisting of 100 kg N, 70 kg P2O5 and 80 kg K2O/ha, and omission treatments without N, P or K.

Yields of transgenic cotton across different locations with ample NPK varied from 3.2 to 4.0 t/ha, with an average of 3.6 t/ha, respectively. Omission of N, P and K resulted in average yields of 2.0, 3.2 and 3.0 t/ha, respectively. The highest yield response was observed with the application of N (1.6 t/ha) followed by K (0.6 t/ha) and then by P (0.4 t/ha). Higher net return of INR 74,036/ha and benefit-to-cost (B:C) ratio of 2.05 were realized with ample NPK treatment. The net returns were reduced by 71, 19 and 27% with the omissions of N, P and K, respectively, from the ample NPK treatment. Post-harvest analysis of the soil is currently underway and plant samples are being measured to determine nutrient uptake. The data generated from this study will be utilized for the development of a decision support tool known as Nutrient Expert® for cotton.