Georgianne Moore, Texas A&M AgriLife
A new study in the journal Nature Ecology & Evolution may help farmers irrigate crops more efficiently, with a better understanding of how much water is actually used beneficially by plants in a given environment.
Researchers analyzed data from 45 field stations representing different climates around the world, from jungles to deserts, trying to determine the optimal rainfall where plants are most productive before water is lost to evaporation or runoff.
While the study was not tailored specifically to irrigation, lead author Stephen Good at Oregon State University said the findings do have a practical link to agriculture.
“If you’re irrigating a field, you want to make sure the water you’re putting on is actually being used, and not just being evaporated off,” Good said.
The study is based on measuring transpiration, or the process by which moisture is carried through plants from the roots to the leaves, where it changes to vapor and is eventually released back into the atmosphere.
Good, a hydrologist and assistant professor at OSU, said transpiration is the part of the water cycle that is most linked to the productivity of plants.
“When you think of water as a resource, transpiration is the total amount of water a plant is able to use,” Good said.
Despite its importance, Good said transpiration is poorly understood. What the study finds is a general relationship between transpiration and climate — that essentially there is a “sweet spot” for rainfall, not too wet and not too dry.
“You tell me the climate and aridity in that climate, and I can tell you how much water the plant can use in transpiration,” Good summarized.
With that information, growers could make key management decisions such as cropping systems and irrigation rates to maximize yield while reducing input costs. Good said researchers are now conducting similar studies on the ground in some of Eastern Oregon’s more arid climates, including Hermiston, Milton-Freewater, Dufur, Maupin and Madras.
Georgianne Moore, co-author of the study and an associate professor at Texas A&M University, said their modeling shows how rainfall is split between plant use, evaporation, runoff and interception, where water doesn’t actually make it into the soil.
“We produced a map based on the model to show what parts of the world will fall off the curve and no longer use their rainfall as efficiently for beneficial growth,” Moore said in a statement released through OSU.
One other wrinkle in the equation is climate change, which Moore suggests will continue to shift away from intermediate climates and more toward extremes, with wet areas getting wetter and dry areas getting drier.
“There could be big consequences, as it will affect forests, grasslands, savannas and deserts,” Moore said. “Scientists can now use the model we have to help make predictions about the future of these plant communities.”
Changing climates and transpiration could significantly influence agricultural systems as well, Good said.
“If we move to a drier climate, or if the climate changes in Oregon, we can expect a decrease in the transpiration of plants,” he said.