RAPID-DETERMINATION OF SHOOT NITROGEN STATUS IN RICE USING NEAR-INFRARED REFLECTANCE SPECTROSCOPY

Near infrared reflectance (NIR) spectroscopy is a rapid, cheap, simple technique which can be used to make quantitative analyses of the concentrations of nutrients in plant tissue. The application of NIR to determine nitrogen in rice was examined. The absorbance spectrum of rice (Oryza sativa L) shoot tissue was similar to that of the temperate cereal wheat even though rice tissue has a much higher silica content. A 19-filter NIR instrument was calibrated to estimate the nitrogen content of rice shoots with between 0.8 and 3.50% N by the Kjeldahl technique. The calibration model developed used three wavelengths to account for 96% of the variation in sample Kjeldahl nitrogen concentration. This model was validated using 67 samples comprising five rice varieties grown on farms in two seasons in southern New South Wales. The standard error of prediction of the model was 0.15% N. A tissue testing service using this NIR calibration is now operational for rice crops in southern New South Wales.