Application of UV-Spectrophotometry in the Nutrition Diagnosis of Nitrogen in Hybrid Cotton

Under drip irrigation,field experiments were conducted to test the nitrogen diagnosis of hybrid cotton and nitrogen fertilizer recommendation.UV-Spectrophotometry was applied to measure NO3-concentration of the fourth expanding petiole at different growth stages of hybrid cotton.The results showed that there were distinctly significant linear correlation between the nitrate concentrations in the fourth expanding petiole of hybrid cotton and the application amounts of N fertilizer at the budding stage,early blooming stage,peak bolling stage and bolling stage.Also,distinctly significant correlation between the nitrate concentrations and the cotton yield was observed.The critical values of nitrate concentrations were respectively 18596.3,2625.7,3431.3 and 2462.8 mg L-1 at the budding stage,early blooming stage,peak bolling stage and bolling stage of hybrid cotton.Under the drip irrigation,the optimal yield was 6413.7 kg hm-2,and the corresponding optimal rate of N fertilizer was 348.1 kg hm-2.According to the relationship between the nitrate concentrations in the leaf petiole at different stages and the application rates of N fertilizer and cotton yield,the N recommending models at different growth stages were developed.