Abstract

Modern cotton cultivars require more potassium (K) and its deficiency during peak bloom and boll setting period adversely affects the seed-cotton yield. The objectives of the present study were to determine the adequate K dose for the modern, transgenic cotton cultivar (Bt.CIM-616) grown on an arid light soil, to evaluate the effects of a split K application, and to quantify the contribution of additional foliar K applications on seed-cotton yield and its components. Two-year (2014-15) field experiments were conducted at the Central Cotton Research Institute, Multan, Pakistan, in two sets. In set-I, three K doses (0, 100 and 200 kg K₂O ha^-1) were applied at sowing or were split into two or four equal applications of 50 kg K₂O ha^-1 (pre-planting and 45 days after sowing or pre-planting, 30, 45 and 60 days after sowing) respectively. In set-II, the impact of preplanting applications of 0, 100 and 200 kg K₂O ha^-1, followed by four foliar sprays of 2% K₂SO₄ were evaluated for plant structure and yield components. The results revealed that supplemental K is a prerequisite for modern transgenic cotton grown on poor arid soils, as it ensures sufficient plant growth and development and subsequently increases the seed-cotton yields to considerable levels. However, basal K application alone would not fulfil the cotton yield potential. Splitting the annual dose to 2-4 mid-season sidedress applications significantly improved seed-cotton yield. Nevertheless, a basal K application, followed by four foliar sprays of 2% K₂SO₄ during the season resulted in the highest yield, obtaining up to 40% more yield than the non-fertilized control, and 10-15% more than that of the split soil-applied K. These results demonstrate the importance of matching plant K status to the dynamic crop demands for this nutrient, particularly in modern transgenic cotton cultivars.