ESTIMATING POTATO LEAF-AREA INDEX FOR SPECIFIC CULTIVARS

The growth and duration of crop leaf area determines the amount of sol ar radiation intercepted by the canopy and therefore influences the ex tent of photosynthesis, evaporation, transpiration and final dry matte r yield. The objective of this study was to develop cultivar specific relationships to estimate the daily leaf area index (LAI) for the pota to crop (Solanum tuberosum L.) that included the effects of available soil water. The model is divided into three LAI growth stages, the dur ations of which are partially related to potato heat units (PHU). The LAI in the first stage is estimated from a cultivar specific leaf area -based radiation use efficiency index with a soil water reduction fact or. The second stage involves the maintenance of a constant LAI with t he duration related to both PHU and a soil water index that can accele rate senescence. The final stage includes a decrease in the LAI from a maximum to zero in response to a cultivar specific PHU accumulation. Model simulations compared favourably with independent LAI measurement s obtained with a LI-COR plant canopy analyzer over two seasons.