Field trials have been conducted on two types of soil:Semihydromorphic soil and red earth in Zhejiang province,where available K content in these soils was low.Cotton plants (Gossypium hirsutum L.) grown on the above soils showed a signficant correlation between K content in leaves and lint yield at different stages of growth.According to the degree of K-deficiency of cotton plants response to the exchangeable K in soils,four catagories may be divided:1.exchangeable K>90 ppm,no K-deficiency;2,exchangeable K=70-90 ppm,latent deficiency;3.<70 ppm,deficiency;4.<50 ppm,severe deficiency.A high significant positive correlation between K content in cotton leaves and exchangeable K in soils,r=0.928.The regression equation is:y=0.1009-1-0.00467 x where,is K content in cotton leaves at flowering-bolling stage,x is exchangeable K in soils.