ReviewWhat about keeping plants well watered?

•Deficit irrigation is the general way to save water.•Some literatures indicate elevated water use efficiency with low soil water tension.•Keeping plants under low water tension could be worth when water is more available.•Under water scarcity the slogan is “more crop per drop”.•Under water availability the slogan could be “more drop, more crop”.

Deficit irrigation agriculture is defined as the application of water below crop requirements. Water use efficiency is the main trait used to evaluate the efficiency of agriculture under deficit irrigation, determined as the harvested biomass per applied volume of water. Agriculture under deficit irrigation is based on the widely accepted belief that it saves water and increases water use efficiency, as opposed to agriculture under optimal water availability. Nevertheless, there is considerable literature reporting high crop yielding in response to high water availability without wasting water, because the highest water use efficiency was achieved with a very light decrease in water availability, still inside the field capacity (10-33 kPa of soil water tension). The deficit irrigation concept is well summarized by the slogan “more crop per drop”. In this review, we would like to explore another slogan: more drop, more crop. We discuss research carried out which demonstrates that when the criterion to schedule irrigation is the soil water tension - which is the real expression of water availability in soil - the highest water use efficiency is achieved when plants are still well watered, and not when there is expressive water deficit. Therefore, low soil water tension seems to be worthy for agriculture under high water availability, while more severe deficit for agriculture under low water availability.