Increasing agricultural water use efficiency to meet future food production

With the world’s population set to increase by 65% (3.7 billion) by ∼2050, the additional food required to feed future generations will put further enormous pressure on freshwater resources. This is because agriculture is the largest single user of fresh water, accounting for ∼75% of current human water use. At present ∼7% of the world’s population live in areas where water is scarce. This is predicted to rise to a staggering 67% of the world’s population by 2050. Because of this water scarcity and because new arable land is also limited, future increases in production will have to come mainly by growing more food on existing land and water. This paper looks at how this might be achieved by examining the efficiency with which water is used in agriculture. Globally, in both irrigated and rain fed agriculture only about 10–30% of the available water (as rainfall, surface or groundwater) is used by plants as transpiration. In arid and semi-arid areas, where water is scarce and population growth is high, this figure is nearer 5% in rain fed crops. There is, therefore, great potential for improving water use efficiency in agriculture, particularly, in those areas where the need is greatest. The technical basis for improving agricultural water use efficiency is illustrated. This may be achieved by increasing the total amount of the water resource that is made available to plants for transpiration and/or by increasing the efficiency with which transpired water produces biomass. It is concluded that there is much scope for improvement, particularly, in the former and that future global change research should shift its emphasis to addressing this real and immediate challenge.