Irrigating more U.S. crops by mid-century will be worth the investment
- The benefits of irrigation will outweigh the costs in many areas of the United States, especially in the Midwest and Great Plains.
- The availability of water will be a limiting factor in some areas, especially in the Southeast.
- These findings could help farmers and policymakers make decisions about irrigation in the face of climate change.
Currently, less than 20 percent of U.S. croplands are equipped for irrigation. With climate change projections showing higher temperatures, increased drought conditions, and shifting precipitation patterns, irrigating more crops in the United States will be critical to sustaining future yields.
In a new study, Michigan State University landscape hydrologist Anthony Kendall and his colleagues found that, by the middle of the 21st century under a moderate greenhouse gas emissions scenario, the benefits of expanded irrigation will outweigh the costs of installation and operation over an extended portion of current U.S. croplands.
The results show that by mid-century, corn and soybeans that are currently rainfed would benefit from irrigation in most of North Dakota, eastern South Dakota, western Minnesota, Wisconsin and Michigan. Soybean farmland that relies on rain throughout parts of Indiana, Illinois, Ohio, Kentucky, Kansas and Oklahoma would also benefit from irrigation. These findings were recently published in Communications Earth & Environment, an open-access journal from Nature Portfolio.
Working closely with Trevor Partridge and a group at Dartmouth College, Kendall and an MSU contingent provided their expertise in agrohydrology, or the study of water in agriculture. MSU pioneered methodology to calculate the cost of pumping irrigation water at every location in the United States. Dartmouth used those costs, compared to modeled crop yield benefits of irrigation, to determine the potential profitability of irrigation in the future.
“This is the first study that looks at not just the potential feasibility of irrigation in areas that are currently "dryland" or "rainfed" agriculture, but also whether it would make sense both economically and from a water resource perspective,” said Kendall, an assistant professor in the Department of Earth and Environmental Sciences in the MSU College of Natural Science.
Installing, maintaining, and running irrigation equipment comes at a significant cost to farmers, as much as $160 per acre per year.
"Our work essentially creates a U.S. map of where it will make the most sense to install and use irrigation equipment for corn and soybean crops in the future," said first author Trevor Partridge, a Mendenhall Postdoctoral Fellow and research hydrologist with the U.S. Geological Survey Water Resources Mission Area, who conducted the study while working on his PhD at Dartmouth.
The High Plains region, including Nebraska, Kansas, and northern Texas, has historically been one of the most heavily irrigated areas, and was found to have the highest current economic returns for irrigation. However, the increasing costs of drought are pushing farmers to invest in irrigation throughout regions of the Corn Belt and southeastern U.S., and the long-term economic return on these investments is difficult to predict.
To conduct the cost-benefit analysis of irrigating corn and soybeans, the researchers ran a series of crop model simulations. They applied several global climate projections that span the range of potential future climates—hot and dry, hot and wet, cool and dry, cool and wet, each relative to the average climate projection—to simulate future crop growth under fully irrigated or rainfed conditions.
For each climate scenario, the crop model was run for both corn and soybeans across all cultivated areas in the U.S. The crop model simulations examined three periods: historical (1981-2010), mid-century (2036-2065), and end-of-century (2071-2100) under moderate and high greenhouse gas emissions scenarios. The simulations factored in county-level crop management and growth data from the U.S. Department of Agriculture National Agricultural Statistical Service, including planting, maturity, and harvest dates.
To determine the economic benefits of irrigating—the team calculated the additional simulated crop yield from irrigating and the corresponding increased market value that could be expected—relative to the irrigation costs, which included the electricity required to pump groundwater and distribute it over the field, and associated expenses per acre to own and operate the irrigation system. The team investigated not only where and when it makes sense to install irrigation for corn and soybeans but also if there will be enough water to do so.
“We calculated the ‘irrigation water deficit’, which is the difference between how much irrigation would be optimal for the plants to grow, and how much groundwater is recharged each year,” Kendall said. “You don't want to use more water than enters the ground at that location or you will deplete groundwater resources.”
The results show that by mid-century there will likely be enough water to irrigate soybeans in Iowa, Wisconsin, Ohio, and northern Illinois and Indiana, but not corn. Iowa is the largest producer of corn in the U.S. Groundwater resources for irrigation were found to be the most abundant in the southeast U.S., especially in the lower Mississippi Valley where agriculture is less intensive. However, in this region the benefits of irrigation are minimal.
If farmers are incentivized to use more water for irrigation, it will lead to greater stress on key aquifers, such as the Ogallala Aquifer in the Great Plains — the largest aquifer in the U.S., providing water to eight states, and supporting one the most extensively irrigated areas for corn and soybeans. This will have to be taken into consideration.
With greater warming, such as end-of-century under a high greenhouse gas emissions scenario, heat stress will dominate impacts on crop yields and reduce the effectiveness of irrigation as an adaptation strategy throughout most of the U.S., especially for corn. Corn typically has a higher yield than soybean, but soybeans are more heat tolerant, don't require as much water, and have a slightly shorter growing season.
“Our model results show that growing soy will be profitable and need less water than corn, suggesting that farmers may lean more toward a reliable soy crop that they can irrigate, versus a corn crop that might need too much water,” Kendall said.
When it comes to irrigation, farmers must consider a range of complex and competing factors: previous yield performance, crop market values, energy costs, economic incentives, and seasonal weather forecasts. The researchers hope that their analysis can be used to help agricultural and water resource management policies in adapting to a warmer climate.The senior author on this study was Jonathan Winter, an associate professor of geography and lead of the Applied Hydroclimatology Group at Dartmouth. Bruno Basso, John A. Hannah Distinguished Professor at MSU; Lisi Pei, MSU and Georgia Institute of Technology; and David Hyndman, University of Texas at Dallas, also contributed to the study.
Banner image: Changing climate will bring longer growing seasons with more infrequent and extreme rains. Across the country, farmers once reliant on weather alone to provide water for their crops will turn to irrigation to increase yields and profits—and put new stresses on limited water resources. Credit: Aqua Mechanical/Flickr