MODIFYING ‘PEACH’ TO MODEL THE VEGETATIVE AND REPRODUCTIVE GROWTH OF ALMONDS

A carbon budget computer simulation model for almonds has been developed by modifying the existing PEACH model (DeJong et al., 1996). The model simulates, on a daily basis, the seasonal carbon supply and demand for reproductive and vegetative growth. The concept behind the model is that the tree grows as a collection of semiautonomous interacting organs competing for carbohydrates, whose partitioning is dependent on the organ growth potentials. Although peaches and almonds are closely related, they have some architectural and physiological differences due both to genetic and management-induced (e.g. pruning and training systems, thinning, etc.) causes. These differences required modification of the parameters of some of the equations used in the main parts of the model, the carbon supply and demand modules, although the main structure of the PEACH model was not changed. Carbon assimilation (supply) is simulated as a function of solar radiation, minimum and maximum temperatures, degree-days, tree light interception, and leaf photosynthetic rates. Respiration and growth are simulated to determine the various organ carbon demands; carbon partitioning is simulated based on sink strength (organ growth potential) and source-proximity of tree organs as well as on carbohydrate availability. The model provides a framework for integrating environmental and physiological factors controlling carbohydrate supply and demand for growth of almonds at the orchard level and indicates potential avenues of research related to growth and productivity. Results of the first model simulations are presented.