Crop coefficient (K c) for apple: comparison between measurements by a weighing lysimeter and prediction by CropSyst

Accurate prediction of crop coefficient (K _c) is necessary for proper irrigation management. We explored CropSyst for determining irrigation requirements of apple trees and for accuracy of K _c prediction. Values of K _c were compared to those obtained, over 2002–2010, from lysimeter-grown trees. Over these years, trees had different ratios of height (H) to width (W). CropSyst predicted irrigation requirements using tree light interception and water uptake sub-model components. Parameters of the model were adjusted using data obtained from the lysimeter in 2010. Tree light interception sub-model was verified by 2007 data. After parameterization, good agreement was found between simulated and measured K _c over different seasons. The porosity coefficient of the canopy was related to changes in tree’s H/W ratio and leaf overlapping. Accordingly, different porosity values could be estimated for each year. When yearly changes in canopy porosity was considered, CropSyst improved K _c prediction and generated relevant information for managing irrigation under changing canopy shape for apple trees.