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.