Managing Global Resources for a Secure Future

To explore a centralized signal for the evaluation of plant water status based on soil water status, two greenhouse experiments investigating the effect of the relative distribution between soil water and roots on wheat and rice were conducted. A significant relationship was found between the plant water deficit index (PWDI) and the root-weighted (rather than the arithmetic) average soil water content (SWC) over root zone. The traditional soil-based approach for the estimation of PWDI was improved by replacing the arithmetic averaged SWC with the root-weighted SWC to take the effect of the relative distribution between soil water and roots into consideration. To validate the root-weighted approach (RWA) and to investigate its effects on irrigation scheduling, plant growth and yield, water consumption and use efficiency when applied to trigger irrigation. A lysimetric experiment and a field experiment were conducted, in which different climatic zones, crop species, soil types, PWDI estimation approaches, irrigation methods and levels were involved. Although both PWDI estimations failed to capture the sharply changing theoretical values resulting from transient fluctuations of weather conditions or irrigation events, the RWA was found to be more reliable than the traditional approach. More precisely timed irrigation scheduling by the RWA resulted in higher irrigation frequency and quantity, and thus higher aboveground biomass, leaf area, grain yield, and transpiration mostly without significant decrease in water use efficiency. Further improvement is necessary to consider the effects of plant recovery from water stress after re-watering, weather conditions, and choice of soil water stress response function on RWA based irrigation scheduling.