The effects of potassium nutrition [0, 6.25, 12.50, 25.00 g(K) m -2 of K 2 SO 4 or KCl] on gas exchange characteristics and water relations in four cultivars (CIM-448, CIM-1100, Karishma, S-12) of cotton were assessed under an arid environment. Net photosynthetic rate (P N ) and transpiration rate (E) increased with increased K supply. The leaf pressure potential (Ψ p ) increased significantly by the addition of 25.00 g(K) m -2 compared to zero K level. The water use efficiency (P N /E) was improved by 24.6 % under the highest K dose compared to zero K. There were positive correlations (0.99 ** , 0.98 ** , 0.95 ** , 0.97 ** ) between K-doses and P N , E, Ψ p , and P N /E, respectively.

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A field experiment was conducted at Central Cotton Research Institute, Multan, Pakistan on Miani soil series, silt loam soil (Calcaric, Cambisols and fine silty, mixed Hyperthermic Fluventic Haplocambids) to assess the response of four cotton (Gossypium hirsutum L.) cultivars to potassium (K) fertilization. The treatments consisted of four cotton cultivars (CIM-448, CIM-1100, NIAB-Karishma, S-12), four potassium rates (0, 62.5, 125, 250 kg K ha À1 ), and two sources of potassium fertilizer [muriate of potash (KCl) and sulphate of potash (K 2 SO 4 )]. The cotton cultivars differed ORDER REPRINTS significantly in response to various potassium fertilizer levels and its sources with respect to seed cotton yield and its components. The highest yield was obtained with the application of 250-kg K ha À1 , however, it was economical to add 125 kg K ha À1 . Seed cotton yield of cv. CIM-448 was considerably greater than that of the other cultivars in K-unfertilized treatments, which was related to cultivar differences in K uptake efficiency in utilizing native potassium nutrient. Potassium added as muriate of potash caused a significant depression in seed cotton yield than that of sulphate of potash. The increase in yield seemed to have resulted largely from the higher K concentration of leaf tissues at bloom stage and available soil-K because of potassium application. A significant relationship between the yield and number of bolls per plant (r ¼ 0.92 ÃÃ ) and boll weight (r ¼ 0.85 ÃÃ ) indicated that these two growth attributes were responsible for enhancing the quantum of final harvest of seed cotton.

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