Seed cotton yield, ionic and quality attributes of two cotton (Gossypium hirsutum L.) varieties as influenced by various rates of K and Na under field conditions

Cotton is more sensitive to low K availability than most other major field crops, and often shows symptoms of K deficiency in soils not considered K deficient. Field investigation was conducted at Sahiwal to study the effect of different rates of K and Na application on seed cotton yield, ionic ratio and quality characteristics of two cotton varieties. Ten soil K: Na ratios were developed after considering indigenous K, Na status in soil. The treatments of K+Na in kg ha-1 to give K:Na ratios were as: 210+ 60 (3.5:1) i.e. control, 225 + 60 (3.75:1), 240 + 60 (4:1), 255 + 60 (4.25:1), 270 + 60 (4.5:1), 210 + 75 (2.8:1), 225 + 75 (3:1), 240 + 75 (3.2:1), 255 + 75 (3.4:1) and 270 + 75 (3.6:1). Control treatment represented indigenous K, Na status of soil. The experiment continued until maturity. Maximum seed cotton yield of NIBGE-2 was observed at K: Na ratio of 3.6:1. Variety NIBGE-2 manifested greater seed cotton yield than MNH-786. Leaf K: Na ratio of two cotton varieties differed significantly (p < 0.01) due to varieties, rates of K and Na and their interaction. Variety NIBGE-2 maintained higher K: Na ratio than MNH-786 and manifested good fiber quality. There was significant relationship (R2 = 0.55, n = 10) between K: Na ratio and fiber length and significant relationship (R2 = 0.65, n = 10) between K concentration and fiber length for NIBGE-2. There was also significant relationship (R2 = 0.91, 0.78, n = 10) between boll number and seed cotton yield for both varieties. The increase in yield was attributed to increased boll weight.