Positional Distribution of Leaf Color and Diagnosis of Nitrogen Nutrition in Rice Plant

Greenness and nitrogen content of each leaf on main stem of different japonica and indica rice varieties under different nitrogen levels were investigated. The results showed that the fourth leaf from the top exhibited active changes with changing plant nitrogen status. When plant nitrogen content was low, color and nitrogen content of the fourth leaf were obviously lower than those of three top leaves. With the increasing plant nitrogen content, color and nitrogen content of the fourth leaf increased quickly, and the difference in color and nitrogen content between the fourth leaf and three top leaves decreased. Thus, the fourth leaf from the top is a good indication of plant nutrition status. In addition, color difference between the fourth and the third leaf from the top was highly related to the plant nitrogen content, regardless of variety and development stage. Therefore, color difference between the fourth and the third leaf from the top can be widely used for diagnosis of plant nutrition status. The results also indicated that a minimized color difference between the fourth and the third leaf from the top at the stages of the critical affective tillering, the emergence of the second leaf from the top and heading is a symbol of high yield, and that plant nitrogen content of 27g·kg -1 DW for japonica rice and of 25 g·kg -1 DW for indica rice are critical nitrogen concentration.