Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2007
Publication Date: 7/29/2008
Citation: Evans, R.G., Sadler, E.J. 2008. Methods and Technologies to Improve Efficiency of Water Use. Water Resources Research. 44,W00E04, doi:10.1029/2007WR006200.
Interpretive Summary: Irrigation is critical to our modern world society and lifestyles; it provides at least 40% of our total food and fiber supply. Despite current problems and negative perceptions in many sectors of society, irrigation will continue to be a necessary and important component of the world’s well being and growth. At the same time that both irrigated agriculture’s land base and water supplies are being depleted, it is being asked to produce even more. This will require a major paradigm shift related to water use within the next 25 years in many areas in the West as well as in humid locations such as South Carolina, Georgia and Arkansas and many other areas in the world. Both urban and rural users will need to lower and adjust their expectations on how and where available water will be used; and they may have to accept much higher water and food prices as a result. Genetic approaches will be a necessary part of more efficient irrigated production (both typical and supplemental). However, there is a much greater possibility of reducing water consumption with improved management of water than with biotechnology and breeding, at least in the short term. Rural and urban irrigators will have to improve productivity per unit of water consumed (WUE). However, it will take major, systematic cultural, managerial, engineering and institutional changes. This must be supported by system-wide enhancement of water delivery systems, advanced site-specific irrigation technologies that include self-propelled sprinklers and microirrigation systems, and other supporting monitoring, modeling and control technologies. Decision support tools will be needed to assist growers and managers in optimizing the allocation of limited water among crops, selection of crops by regions, and adoption of appropriate alternative crops in drought years. The paradox is that agriculture needs to increase production to meet societal needs; however, increasing WUE usually means reduced yields. The net result will probably be targeting inputs to meet yield goals somewhere near the economic optimum. Carefully managed deficit irrigation on agronomic crops provide the greatest potential for substantially reducing agricultural water use due to the larger land areas that are involved. High value crops may also produce some water savings through various deficit irrigation strategies, but their impact will be much lower because they generally occupy less than 10% of irrigated area (location-specific). However, deficit irrigation strategies still must be developed for most crops. Advanced irrigation technologies and state-of-the art delivery systems, however, will be needed to be able to be able to fully implement successful deficit irrigation strategies. Precision agriculture tools such as site-specific water and nutrient applications will play an important role. Managing and developing infrastructure and policies for water security to equitably satisfy the demands of all users of this limited resource will be a challenging and lengthy task. Changes in policy and incentives will clearly become necessary. However, water and land resources and their many complex and competing uses must be considered in a comprehensive regional and international framework. Improvements should be system-wide, not concentrated on only one or two components of the hydrologic system. Irrigated agriculture can reduce its water use while maintaining reasonable production levels. However, the challenges are substantial. In this era of declining field research on cropping systems, we must determine the specific knowledge and technologies required to accomplish this sustainability. To function as a society, we have to trust enough water will be available to satisfy all the needs for food, fiber, feed, and fuels in addition to environmental, recreation and municipal requirements. Nevertheles
Technical Abstract: The competition for existing freshwater supplies will require a paradigmatic shift from maximizing productivity per unit of land area to maximizing productivity per unit of water consumed per unit of land. This shift, in turn, will demand broad systems approaches that physically and biologically optimize irrigation relative to water delivery and application schemes, rainfall, critical growth stages, soil fertility, location, and weather. Water can only be conserved at a watershed or regional level for other uses if evaporation, transpiration, or both are reduced and unrecoverable loses to unusable sinks are minimized (e.g., salty groundwater, oceans). Agricultural advances will include implementation of crop location strategies, conversion to crops with higher economic value or productivity per unit of water consumed, and adoption of alternate drought tolerant crops. Emerging computerized GPS-based precision irrigation technologies for self-propelled sprinklers and microirrigation systems will enable growers to apply water and agrichemicals more precisely and site-specifically to match soil and plant status and needs as provided by wireless sensor networks. Agriculturalists will need to have flexibility in managing the rate, frequency, and duration of water supplies to optimally allocate limited water and other inputs to crops. Nonagricultural water users will need to exercise patience as tools reflecting the paradigmatic shift are actualized. Both groups will need to cooperate and compromise as they practice more conservative approaches to freshwater consumption. Key Words: Water use efficiency, irrigation, irrigation systems, water scarcity, deficit irrigation, water management