Colorimetric determination of nitrogen for evaluating the nutritional status of rice

The Orange—G dye colorimetric method for protein determination, was evaluated as a rapid, simple, quantitative method to determine the nitrogen nutritional status of rice. The amount of dye adsorbed by dry, ground (40 mesh) most recently matured leaf tissue ("Y leaves"), at three stages of rice development, was highly correlated with % N by the micro‐Kjeldahl method. The regression line of this relationship was different, however, at each stage of maturity. With the ratio of g plant material to ml of 0.12 dye solution as 0.2:20 for the raidtillering growth stage and 0.2:15 for samples taken at growth stages thereafter, one regression line fits all stages where % N = ‐0.34 + 0.9703 dye adsorbed (g/100 g). The method was tested on 60 leaf samples taken at three different stages of rice plant development. There was no difference at the .01% of statistical significance between the mean values of the dye and Kjeldahl method. The standard deviation of the difference between the two methods was ±0.2% over a range of 1.75 to 5.35% nitrogen.