Hyperspectral vegetation indices for predicting onion (Allium cepa L.) yield spatial variability

An agronomic research was conducted to evaluate the spatial variability of an onion crop, with the aim to test Vegetation indices (VIs) as a tool to detect different yield areas. Eleven VIs were derived from geo-referred hyperspectral readings taken at bulbification stage. Eight VIs showed significant regressions with yield, and grouped in four clusters according to statistical analysis (H = high; Ms and Mi as medium superior and inferior; L = low). Maps were elaborated with ordinary Kriging. At a visual assessment, many VIs appeared similar to yield map. The surface analysis revealed that all VIs accurately detected an L area (top of maps) characterized by heavy soil constrains, and the H area on the left side of the map (button and upper part). The best estimation of the total field yield was obtained by the so-called Soil-line vegetation indices and in particular by TSAVI. This study reinforces the possibility of assessing onion yield by spectroradiometric measurements at field scale.