New Article Traces Aspects of the History of Irrigation in the Great Plains and Water Productivity
Irrigation has been part of agriculture in the Great Plains, which Nebraska is right in the middle of, as far back as we have records and probably much longer than that. The region has productive soils and a good climate to grow crops but does not receive enough rain to produce top yields. In addition, the rain that is received is inconsistent, thus irrigation can supplement the water the crops need between rains allowing farmers to produce a good crop every year. The increased yields and year-to-year yield stability has led to a better economic environment in the region as well.
A recent article by Dr. Steve Evett and others traces the history of irrigation in the Great Plains region from a geographical, technical and political perspective, as well as how it has impacted the water resources.
After some prehistoric irrigation in the Great Plains, irrigation development began in the late 1800s, starting with projects diverting water from rivers to fields. Eventually, irrigation projects also included reservoirs for storing water along with complex systems of canals to deliver water to fields up to 100 miles away. Groundwater use was initially small; however, improvements in well technology made it practical for many producers to be able to access groundwater. With the invention of the center pivot, the area of irrigated cropland grew to over 22 million acres in the Great Plains. Irrigation has been a significant factor in the high levels of agricultural production in the region, resulting in the Great Plains being referred to as a “bread basket.”
The article, entitled “Past, Present and Future of Irrigation on the U.S. Great Plains” and published by the American Society of Agricultural and Biological Engineers (in the Transactions of the ASABE), also put irrigation in the context of its impact on water resources. Today, irrigation in the region is primarily dependent on groundwater (in Nebraska, 91% of irrigation water is from groundwater), although surface water sources continue to be significant. In some locations, the rate of water withdrawal for irrigation has exceeded the rate of aquifer recharge, resulting in declining water levels in the High Plains Aquifer.
In 1972, Nebraska transitioned from a system of Soil and Water Conservation Districts to a system of Natural Resource Districts (NRDs), maintaining local control through a locally elected board, which led to pumping and usage policies that contributed to the reduction in the rate of decline of groundwater levels. Many of these NRDs have imposed an allocation-based system in which producers are allowed to use a specified amount of water in a particular time interval. Further, monitoring of total water pumped from the wells and registration of existing and new wells was made mandatory by the NRDs. Since surface water and groundwater are connected, various needs for in-stream flows have had an impact on how groundwater is managed.
Although irrigation has had an impact on water resources, it has also improved how effectively water is used to produce a crop. The article defines crop water productivity (CWP) as the crop yield divided by the seasonal crop water use (evapotranspiration). In general, irrigated crops in the Great Plains have a CWP approximately double that of crops grown with rainfall alone because of crop water stress between rains or the crop running out of water before maturity. Irrigation allows crops to grow close to their potential yield, in which case the crop functions more optimally and produces more yield for each inch of water consumed. Advances in crop genetics and production practices, including drought-tolerant and high-producing hybrids, have also led to increases in CWP over time. A report from the Daugherty Water for Food Global Institute estimates that CWP for corn and soybean in Nebraska has increased by approximately 75% over 24 years.
Finally, the article highlights the role of technology in the history of irrigation development and its impact on water resources. Over the decades, several different types of technology have resulted in increases in irrigation application efficiency, which is the depth of water stored in the root zone divided by the depth of water applied. Better application efficiencies allow for reduced water withdrawals for irrigation by reducing water losses such as deep percolation past the root zone and runoff from the field. Reduced water losses also reduce negative impacts on water quality (such as nitrate leaching). While crop water use is essential for crop production (beneficial evapotranspiration), some irrigation technologies reduce non-beneficial evapotranspiration (such as excess evaporation from sprinkler applications), which improves application efficiency. Reductions in evapotranspiration (consumptive use) while maintaining yields directly improve the CWP and reduces the amount of water pumped.
Looking forward, water scarcity is even a bigger concern for maintaining a high level of agricultural production in the Great Plains. However, the adaptation and innovation that led to significant advances in the past will likely continue to be helpful in fostering food production while managing water resources. A healthy balance between the use of water for irrigation and conservation of these resources will be key to sustainable use in the future. With potential for continued increases in CWP, water supplies will likely be stretched further than what might be expected based on past rates of water use.
Evett, S. R., P. D. Colaizzi, F. R. Lamm, S. A. O’Shaughnessy, D. M. Heeren, T. J. Trout, W. L. Kranz, and X. Lin. 2020. Past, present and future of irrigation on the U.S. Great Plains. Transactions of the ASABE 63(3): 703-729, doi: 10.13031/trans.13620.
Mekonnen, M., C. M. U. Neale, C. Ray, G. E. Erickson, A. Liska, H. Yang, T. L. Romanelli, and A. Y. Hoekstra. 2019. Nebraska Water Productivity Report. Daugherty Water for Food Global Institute: Lincoln, Neb.
This article was originally published in UNL Water.