Detection of nitrogen and phosphorus nutrient status in bermudagrass using spectral radiance

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Abstract
Nitrogen (N) and phosphorus (P) are two of the most limiting nutrients for crop production. Because of this, continued interest focuses on improving N‐and P‐use efficiency. Spectral radiance measurements were evaluated to identify optimum wavelengths for dual detection of N and P status in bermudagrass (Cynodon dactylon L.). A factorial arrangement of treatments (0, 112, 224, and 336 kg N ha‐1 and 0,29, and 58 kg P ha‐1) was applied to an established bermudagrass pasture for further study using a randomized complete block design. A wide range of spectral radiance measurements (276–831 nm) was obtained from each plot using a PSD 1000 Ocean Optics fiber optic spectrometer. The resulting spectra were partitioned into 10‐nm bands. Added indices were generated to test for correlation of N and P content with spectral radiance. The 435‐nm band (430–440 nm) was found to be independent of N and P treatment, and as a covariate, significantly decreased residual error. Using 435 nm as a covariate, it was found that biomass, N uptake, P uptake, and N concentration could be predicted using 695/405. No index reliably predicted bermudagrass forage P concentration. Spectral radiance has the potential to be used for predicting N and P nutrient status, but further work is needed to document response in different environments.

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