Water balance simulation of a peach orchard using the SWB model

Abstract

Soil Water Balance (SWB) is a user-friendly irrigation scheduling model developed to estimate water use for a wide range of crops. The FAO crop factor option within this model allows one to determine daily irrigation requirements from daily weather data as long as suitable crop parameters are available. The parameters required are the basal crop coefficient, root depth and plant height for the relevant growth stage (i.e. initial, development, mid- and late) and the length of each growth stage as well as a stress day index, the leaf water potential at maximum transpiration and the maximum transpiration rate. Data gained from trees planted in a lysimeter trial in South Africa have been used to develop these parameters for a deciduous peach tree crop (Prunus persica cv. Transvalia). These parameter values differed for first leaf and second leaf trees. The determined values gave very good estimates of water usage when applied in field trials. Evidence is presented to highlight the 2-D variation in the components of the soil water balance of a micro-irrigated hedgerow orchard and suggestions are made as to how these variations should be handled.