YIELD, WATER-USE EFFICIENCY AND NITROGEN UPTAKE IN POTATO - INFLUENCEOF DROUGHT STRESS

A lysimeter experiment was performed to study the optimal allocation o f limited water supply in potatoes. Irrigation regimes equal to 40, 60 and 80% of maximum evapotranspiration (ET) were evenly applied over t he crop cycle. Other treatments involved withholding 80 mm of irrigati on, based on ET, beginning at each of three designated growth stages ( tuber initiation, early and late tuber growth). An irrigated control t reatment, restoring the entire ET, was included for comparison. Contin uous drought stress reduced photosynthesis as irrigation volumes were reduced. Plant biomass and tuber yield decreased almost proportionally to water consumption, so that WUE was roughly constant. N uptake was highest in the control and in 80% ET treatment. Withholding water duri ng tuberisation severely hindered plant physiological processes and pe nalized tuber yield. Reductions in photosynthesis, total biomass and y ield were the greatest when drought was imposed during tuber initiatio n. The earliest stress resulted in the lowest WUE and N uptake. A new crop water stress index (SI) was proposed, which combines atmospheric demand for water and canopy temperature.