Cutting and water deficit effect on water use efficiency of forage species

Water use efficiency (WUE) is a widely used concept connecting different processes directly or indirectly related to biomass production and water used. The different ratios of WUE proposed in the literature are based on agronomical, ecophysiological approaches or combination of them. Water deficit influences plants by closing the stomata, indirectly reducing photosynthesis, leaf extension and growth. Moreover the reduction of transpiration due to stomatal closure is greater than photosynthesis. Furthermore, water deficit changes root growth and distribution, therefore modifying the plant ability to extract water from the soil. The relationship between water deficit and WUE is controversial. Many researchers report higher WUE under water deficit, while others lower. On the other hand, cutting parameters, such as timing, frequency and intensity affect the values of WUE, as they affect the harvestable biomass and evapotranspiration. Nevertheless, the absolute values of WUE vary markedly depending on plant, soil, climatic factors and management practices. Regardless of the method used, WUE could still be considered as a useful selection criterion for superior performance, particularly, in a dry environment.