Reducing water use: more crop per drop
A technique called partial root drying (PRD), developed by Professor Bill Davies at the University of Lancaster and his research team, allows certain crops – everything from tomatoes to cotton – to be grown using up to half the amount of water while producing the same (or nearly the same) yield. This type of technique, which optimises water use to give the highest possible productivity with the smallest amount of water, is known as deficit irrigation.
70% of the world’s fresh water extracted for human use is used for agriculture. Reducing the amount of water crops use is an important challenge because increasingly, water is in short supply in many important food producing regions of the world and, as pressure on water use rises, so can the price of food. This is particularly important in drought-prone countries such as China
PRD works by exploiting the way plant roots signal (PDF) that water is scarce. When one side of an individual plant’s roots are starved of water, signals are sent to the leaves to reduce growth and close leaf pores called stomata, which reduces water use, and loss, respectively. Although the growth rate of the leaves declines, because the other side of the plant is being watered the plant does not wilt and carries on producing fruit bodies, like grapes, apples and so on. Alternating which side of the plant receives water and which doesn’t prevents roots from dying in very dry soil.
|40,000||Number of Olympic swimming pools of irrigation water saved each year in Wuwei City, China using PRD|
|50%||Water use reduction on some crops as a result of PRD|
|4||Number of continents where PRD has been used|
PRD has shown particularly promising effects on root growth in tomatoes and water use efficiency of rice when soil is allowed to wet and dry (the PRD effect) in response to irrigation. These techniques are currently being trialled in China and in other parts of Asia, with support from BBSRC, and significant water productivity increases have been reported for reduced applications of water. In a project led by China Agricultural University, the estimated total saving of irrigation water in China’s Wuwei City catchment using PRD and other deficit irrigation techniques is around 80-100 million cubic metres (32,000 to 40,000 Olympic swimming pools) per year.
PRD has also been applied to wine grapes in Australia, where the technique reduced water use by 40%, and to cotton in Turkey, where water use was reduced by half. However, responses to deficit irrigation are crop specific and research continues to refine the technique.
The Lancaster team’s socio-economic impact assessment (DOC), undertaken in Portugal, Morocco, Turkey and the UK, reported a rapid return on investment in extra relatively low tech irrigation equipment. In the UK this arose from both savings in labour and from the production of better value crops. In the Mediterranean, this payback was from a greater resilience of the cropping system against water scarcity.