Effects of nitrogen supply on water-use efficiency of higher plants

The worldwide increase of food demand and reduced sweet-water availability in some important food-producing regions raised interest in more efficient water use, which has become one of the central research topics in agriculture. Improved irrigation management and reduced bare-soil evaporation have highest priority to increase agronomic water-use efficiency (WUE). Compared to these technical (irrigation) and basic (crop production) management options, effects of nutrient management on WUE were less frequently considered. Twenty-nine publications on nitrogen (N) effects on biomass WUE of container-grown plants are considered in this review. Most of them indicate positive N effects on WUE, and relevance of N effects on intrinsic WUE and unproductive water and carbon loss is discussed. A plot of 90 published data of percent decreases of WUE and dry mass under variable N supply is presented. Extrapolation of biomass WUE from leaf measurements of intrinsic WUE is critically reviewed. The positive correlation between WUE and dry-mass formation suggests that physiological rather than stomatal effects are more important in order to explain positive N effects on WUE.