Critical Levels of Boron in Cotton Plants

Abstract The lower and upper critical boron levels in cotton ( Gossypium herbaceum ‐Etawa), which are not estimated, were determined to provide guideline values for estimating the boron status from deficiency to toxicity. Cotton plants were grown under greenhouse conditions in complete nutrient solution containing boron at levels ranging from 0 to 50 ppm. Plants were harvested after 40 days and analysed for B, Zn, Fe, Mn and Cu. The lower critical levels for boron in roots, young leaves and old leaves were 103, 61 and 78 ppm, while critical nutrient toxicity levels were 129, 80 and 91 ppm, respectively. For the Gossypium herbaceum‐Etawa cultivar, the maximum growth was obtained when 1 ppm boron was applied as H 3 BO 3 in the nutrient solution. High boron concentrations in the nutrient solution were associated with low content of Zn, Fe and Mn in the plants, while boron and Cu concentrations increased with boron supply. Significant correlations were found between B treatments and most response parameters measured.