Increasing agricultural water use efficiency to meet future food production

With the world's population set to increase by 65% (3.7 billion) by similar to 2050, the additional food required to feed future generations will put further enormous pressure on freshwater resources. This is because agricult ure is the largest single user of fresh water, accounting for similar to 75 % of current human water use. At present similar to7% of the world's popula tion live in areas where water is scarce. This is predicted to rise to a st aggering 67% of the world's population by 2050. Because of this water scarc ity and because new arable land is also limited, future increases in produc tion will have to come mainly by growing more food on existing land and wat er. This paper looks at how this might be achieved by examining the efficie ncy with which water is used in agriculture. Globally, in both irrigated an d rain fed agriculture only about 10-30% of the available water (as rainfal l, 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 agricul tural water use efficiency is illustrated. This may be achieved by increasi ng 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 impro vement, particularly, in the former and that future global change research should shift its emphasis to addressing this real and immediate challenge. (C) 2000 Elsevier Science B.V. All rights reserved.