Estimation of Top Nitrogen Content in Rice Canopy Using Optical and Nondestructive Methods

Abstract

The top nitrogen content (TNC) per unit area (g m-2) is an important quantitative index of the condition of nitrogen nutrition in rice production. In this study, the rapid and simple method of estimation of TNC, with the use of the existing nondestructive analyzing instruments chlorophyll meter SPAD-502 and plant canopy analyzer (PCA) LAI-2000, was scrutinized. The analysis in the rice cultivar Nipponbare, conducted in 1997 and 1998, showed a high positive correlation (R2=0.743, P<0.01) between the SPAD reading obtained by the chlorophyll meter and the specific leaf nitrogen (SLN). The leaf area index (LAI) estimated by PCA tended to underestimate the LAI determined by actual measurement by about 20%. Still, the estimation of LAI by PCA was judged to have a sufficient accuracy as a practical technique. A high positive correlation (R2=0.866, P<0.01) was obtained between the product of the SPAD reading and LAI, and the leaf nitrogen content (LNC) per unit area (g m-2). LNC and TNC also showed a very high correlation (R2=0.988, P<0.01). The product of the SPAD reading and LAI, and TNC also gave a high positive correlation (R2=0.847, P<0.01). These results indicated that the method described in this study was effective as a simple and rapid method for the estimation of TNC per unit area.