The Future of Desert Agriculture
Changes in Water Supply Allocation and Source in Southwest Agriculture
Recent severe drought in the Southwest U.S. has raised concerns about agricultural water use in the region. Crop production is heavily reliant on irrigation and the conveyance infrastructure built to move water across watersheds to various growing regions. Recent models suggest that Colorado River water users are going to soon enter shortage conditions (Figure 1), which will reduce surface water deliveries to growing areas in Arizona and Nevada (Figure 2), while allotments to California and Mexico remain unchanged. Growers in the irrigation districts that receive less water from the Colorado River will be forced to rely more on surface water supplies in local watersheds and/or pump groundwater to help augment their water needs. Any changes in an irrigation source, especially with the switch to groundwater, presents water quality challenges such as high sodium, chloride, boron and bicarbonates that can have a negative impact on yields and crop quality.
Thus, the future of desert agriculture will require water users to monitor and adjust to changes in water quantity and quality. Water quality can be measured using common laboratory procedures and so that the best water treatment practices can be used. Changes in water quantity and quality can be managed to positively influence irrigation efficiencies, as described below:
Conveyance Efficiency – Conveyance efficiency is the efficiency of water transport in canals and ditches (National Resources Management and Environmental Department - Irrigation Efficiencies). Conveyance efficiency can be influenced by lining ditches and reducing water losses via leakage and evaporation, while water is moving across the region.
Irrigation Efficiency -- Irrigation efficiency can be divided into two separate components: 1) Water losses from drainage and evaporation, and 2) The uniformity of water application across the field. If water losses are large, or the application uniformity is poor, efficiency will be low. (Center for Irrigation Technology - Irrigation Systems and Water Application Efficiencies). Irrigation efficiency can also be improved by selecting the correct irrigation system for the crop (e.g., drip, flood, center pivot). Water losses can be reduced by adjusting set times to prevent excess leaching and runoff while still meeting crop demands. Application uniformity can be improved by using modern laser leveling techniques, checking and repairing irrigation nozzles, and avoiding soil surface crusting.
Physical water productivity – Physical water productivity is defined as the ratio of agricultural output to the amount of water consumed (Sharma et al. 2015;Chapter 3 in Managing Water and Fertilizer for Sustainable Agricultural Intensification). This metric can be improved by using sensors or evapotranspiration values to schedule irrigations based on real time conditions and crop use. Sensors can also inform a grower about precise water penetration and rates of water depletion below ground. Physical water productivity can also be improved by selecting the right crop for the amount of water available to a field.
Improved water management is going to become a big part of irrigated agriculture in the Desert Southwest. While some of our growing regions already have high irrigation efficiencies, advancements can always be made for a more sustainable future. Please consult the links below for more information regarding irrigation, sustainability, and conditions on the Colorado River.
Suggested Reading and Links
A Case Study in Efficiency – Agriculture and Water Use in the Yuma, Arizona Area - http://ycwua.org/a-case-study-in-efficiency/
Colorado River – Open Water Data Initiative - https://www.doi.gov/water/owdi.cr.drought/en/
Irrigation Water Management: Irrigation Scheduling - http://www.fao.org/docrep/t7202e/t7202e08.htm
Irrigation Notes - http://cwi.csufresno.edu/wateright/880104.asp
Managing water and fertilizer for sustainable agricultural intensification - http://tinyurl.com/jmc73b3
- Dr. Karl Wyant, Desert Division Agronomist