DETECTION OF NITROGEN AND PHOSPHORUS NUTRIENT STATUS IN WINTER-WHEAT USING SPECTRAL RADIANCE

Nitrogen (N) and phosphorus (P) are major limiting nutrient elements f or crop production and continued interest lies in improving their use efficiency. Spectral radiance measurements were evaluated to identify optimum wavelengths for dual detection of N and P status in winter whe at (Triticum aestivum L.). A factorial treatment arrangement of N and P (0, 56, 112, and 168 kg N ha(-1) and 0, 14.5, and 29 kg P ha(-1)) wa s used to further study N and P uptake and associated spectral propert ies at Perkins and Tipton, Oklahoma. A wide range of spectral radiance measurements (345-1,145 nm) were obtained from each plot using a PSD1 000 Ocean Optics fiber optic spectrometer. At each reading date, 78 ba nds and 44 combination indices were generated to test for correlation with forage biomass and N and P uptake. Additional spectral radiance r eadings were collected using an integrated sensor which has photodiode detectors and interference filters for red and NIR. For this study, s imple numerator/ denominator indices were useful in predicting biomass , and N uptake and P uptake. Numerator wavelengths that ranged between 705 and 735 nm and denominator wavelengths between 505 and 545 nm pro vided reliable prediction of forage biomass, and N and P uptake over l ocations and Feekes growth stages 4 through 6. Using the photodiode se nsor, NDVI [(NIR-red)/(NIR+red)] and NR [(NIR\red)], were also good in dices to predict biomass, and N and P uptake. However, no index was fo und to be good for detecting solely N and P concentration either using the spectrometer or photodiode sensor.