Root-weighted soil water status for plant water deficit index based irrigation scheduling

Indices based on plant water stress or deficit have been extensively employed to aid irrigation scheduling. The objective of this study was to validate a recently proposed approach to estimate plant water deficit index (PWDI) based on root-weighted soil water status 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 2015 and 2016, in which different climatic zones (Beijing and Inner Mongolia), crop species (winter wheat and spring maize), soil types (loam and sandy), PWDI estimation approaches (traditional based on arithmetic average soil water status and root-weighted), irrigation methods (surface and drip irrigation) and levels (full and deficit) 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 root-weighted approach (RWA) was found to be more reliable than the traditional approach based on arithmetic average soil water status. 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.