Correlation Between SPAD Value In Different Sites Of Cotton Leaf And Nitrogen Nutrition Of Cotton Plant, Nitrogen Application Ratio

There is a strong correlation between the chlorophyll content of leaf and nitrogencontent of plant, also there is a good correlation between SPAD value gotten from SPAD-502Chlorophyll meter and the leaf chlorophyll content. So, the SPAD value can be used topredict the crop nitrogen status. Because the size of cotton leaf is more bigger than the testsite of SPAD-502Chlorophyll meter, it is important to decide the most suitable test site ofSPAD-502Chlorophyll meter in cotton leaf.A field and two culture solution experiments were conducted and the SPAD valuesmeasured at17sites in different cotton leaf were used to investigate the correlation betweennitrogen nutrition status of cotton plant and leaf SPAD value under different nitrogenapplication.Main results are:(1) The tip area of the reversed4th cotton leaf from the apex of the main stem is the besttesting site for SPAD value, because there is significant correlation between the nitrogencontent and SPAD values of the4th leaf, and other leaves don’t have it. The correlationbetween the nitrogen nutrition and SPAD values was also different in different determine sitesof inverse fourth leaf, which S3(near tip of leaf) showed the best significant correlationbetween SPAD and N concentration of cotton shoot. The results suggest that the location ofnear tip of leaf in inverse fourth leaf was the most appropriate site to estimate the nitrogennutrition status of cotton with SPAD value.(2) It is not suitable to determine or predict the condition of the soil nitrogen under fieldconditions only using SPAD values. The results showed a good correlation between thecotton growth and nitrogen application rate at different growth stages, and in addition to lateboll, the cotton growth was increased significantly with the nitrogen fertilizer increasing in the range of0-400kg·ha-2for nitrogen. The results of culture solution experiment showedthat there is a good correlation between the nitrogen application rate and the amount of cottongrowth, nitrogen uptake, leaf nitrogen content and leaf SPAD value, and the correlationcoefficient was the0.785,0.876,0.984and0.878, respectively. However, under fieldconditions, it only showed same results in the early flowering and flowering stages.In conclusion, the location of near tip of leaf in inverse fourth leaf was the mostappropriate site to estimate the nitrogen nutrition status of cotton with SPAD value.