Effects of soil potassium level on growth and photosynthetic characteristics of early cotton

【Objective】 The aim of the study was to study the effects of different potassium levels on growth and photosynthesis of early cotton from a field experiment, and to provide theoretical support for potassium management in cotton fields. 【Methods】 Six soil available potassium concentrations were set in a randomized block design, including k₁ (99.77 mg/kg), k₂ (110.90 mg/kg), k₃ (123.48 mg/kg), k₄ (140.13 mg/kg), k₅ (154.43 mg/kg) and k₆ (165.77 mg/kg). The dry matter weight and total potassium content of 10 cotton plants were determined at cotyledon stage, and the dry matter weight, leaf area, leaf net photosynthetic rate, intercellular carbon dioxide concentration, transpiration rate, stomatal conductance, SPAD value and total potassium content of 10 and 5 cotton plants were determined at seedling and bud stage respectively. 【Results】 At seedling stage, cotton plant height and stem diameter was 5.10 cm~6.37 cm and 2.43 mm~3.01 mm respectively, and both increased with the increase of soil available K level. Daily growth amount of plant height and stem diameter was about 0.63 cm/d and 0.12 mm/d from the seedling stage to the bud stage, but there were no significant differences among different soil available potassium levels. The dry matter weight, branch number, budding number, leaf area and daily growth of leaf area of cotton under k₆ treatment were significantly higher than k₁. At seedling stage and bud stage, there were no significant differences in net photosynthetic rate, intercellular carbon dioxide concentration, transpiration rate, stomatal conductance and chlorophyll SPAD value of functional leaves of cotton under different soil available K levels, but the total potassium content of cotton plants and the potassium content of main stems leaves of cotton under different soil potassium levels increased significantly with the increase of soil available potassium levels. 【Conclusion】 In the range of 100mg/kg to 160mg/kg, soil available K level had no significant effect on the photosynthetic characteristics of cotton plant at the early stage, but high K level (> 150 mg/kg) could increase the plant leaf area and the number of fruit branches and ensure the yield structure.