Sensing Light Absorption by Crop Canopy for Estimating Potential Yield in Almonds and Walnuts

Abstract. A knowledge of spatio-temporal variability in potential yield is essential for site-specific nutrient management in crop production. The objectives of this project were to estimate potential crop yield in individual or a block of almond and walnut trees using photosyntetically active radiation (PAR) absorption data obtained from respective tree(s). This project uses proximally sensed PAR absorption data measured using a lightbar mounted on a mobile platform and crop growth model to estimate potential crop yield of almond and walnut trees. Our results showed that the total amount of PAR intercepted by the tree at any time during the day can be found using zenith angle and midday PAR intercepted. The latter can be measured using the Lightbar system or can be estimated using seasonal growth curve. A good correlation was found between measured values of PAR intercepted and estimated values of PAR intercepted. Actual yield from those trees with lower percentage of midday PAR intercepted was found to be closer to their respective potential yield than those trees which intercepted higher amount of incident PAR.