Abstract

A field experiment was carried out to study the effect of graded levels of potassium fertilizers on Bt cotton hybrid MRC-7351 at the Main Agricultural Research Station, University of Agricultural Sciences, Dharwad, India, on a Vertisol under rainfed conditions during 2012-13 and 2013-14. The experiment layout was a randomized complete block design with nine treatments and three replications. A basal application of 75 kg K2O ha-1, 50% more than the recommended dose, gave a yield increase of 13.4%. Foliar potassium nitrate (KNO3) applications at the reproductive phase (70, 90, and 110 days after sowing), doubled the yield increment. Petiole K concentrations were highly correlated with seed cotton yields, suggesting a potential for monitoring tools for plant K status. Improved plant K status also promoted the uptake of other macro and micronutrients, indicating an improved capacity of the root system. Nevertheless, the very low efficiency of the soil K application (20%) calls for an alternative approach of K fertilization practice, such as splitting the dose into several applications during the season. Foliar applications are instrumental in correcting nutrient deficiencies during the reproductive phase, whenever required. Thus, the potential of K fertilizers to enhance cotton production has been clearly demonstrated but is still far from being fully exploited. To maintain profitable production, cotton producers may need to change from traditional soil fertility programs to an integrated system consisting of soil and foliar applied nutrients.