WATER-STRESS AS A CONSTRAINT ON GROWTH IN THE POTATO CROP .1. MODEL DEVELOPMENT

A simple, physiologically based model of the growth and yield of potato crops constrained by water stress is described. In the model, dry matter accumulation is the product of the light intercepted by the plant canopy and the coefficient of conversion of intercepted radiation into dry matter (C). The rate of extension of individual leaves is related to thermal time and used to calculate leaf area index and light interception each day. Tuber yield is calculated from a knowledge of the partitioning of dry matter and of tuber dry matter concentration (D), both of which are described by thermal time, accumulated from plant emergence. Leaf extension rate, C and D are constrained according to the fraction of plant extractable water remaining in the soil profile. The sensitivity of the model to its principal parameters was examined. The model was most sensitive to changes in water use efficiency. Changing C or the amount of available water in the soil profile had smaller effects on the estimate of yield.