Abstract

A hydroponic experiment was performed with three nitrogen application levels to identify the most appropriate site on a cotton leaf to estimate the nitrogen status of a cotton plant from the SPAD value. The results from the hydroponic experiment were compared with those from a field trial. Distinct regional differences in the SPAD value were observed among the 17 measurement sites on the leaf. The leaf tip yielded the highest SPAD value, whereas measurement sites closest to the petiole showed the lowest SPAD values. The correlation between nitrogen status and SPAD value differed among the measurement sites; only sites near the leaf tip showed a significant correlation between SPAD value and nitrogen content of the shoot. The field trial showed the same results. These findings suggest that a location near the leaf tip is the most appropriate site to estimate the nitrogen status of cotton plants from the SPAD value.