Abstract
The number of spikelets per area that optimizes the yield is determined by nitrogen content of paddy rice at heading stage. As the number of spikelets fluctuates in a field, estimation of nitrogen content of rice plant is essential to decrease the variation of the number of spikelets by topdressing. Using pictures taken with a CCD camera on which band-pass filters were mounted, the nitrogen content of rice plant was estimated. The wavelengths of the filters used were 535nm and 670nm, and the coefficient of determination between the total amount of nitrogen and the “Green” NDVI (Normalized Difference Vegetation Index) was R2=0.87.
