Leaf Water Potential Estimated through Hyperspectral Reflectance Indices.

Pressure chamber measurements of leaf water potential (xylem pressure potential) are often used to determine when crops should be irrigated. We investigated the use of  hyperspectral reflectance indices to precisely and accurately determine cotton leaf water potential as an alternative to use of the slower and more labor-intensive pressure-chamber procedure. Spectra were collected from 400 to 2460 nm using a spectroradiometer. Indices for calibration were developed by calculating all possible ratios of radiance values representing 183 regions of the spectrum, and used in simple linear regression against xylem pressure potentials. The resulting regression equations were applied to an external validation data set collected from a contrasting growth environment. Hyperspectral reflectance indices were established providing precise and accurate indication of leaf water potential (xylem pressure potential) with sufficient sensitivity to direct economics-based irrigation scheduling. Furthermore, hyperspectral reflectance patterns can be used for simultaneous and sensitive estimation of leaf nitrogen concentration in real-time.