'The most crop per drop'

Dr. Mazin Saber is a postdoc who works with the Yuma Center for Excellence in Desert Agriculture. He uses the tripod-shaped Eddy Covariance system to his left to collect date from the plant.

In Yuma, farmers and growers have been trying to change their practices to better conserve water. A private and public partnership through the University of Arizona called the Yuma Center for Excellence in Desert Agriculture aims at contributing to that by finding out exactly how much water a crop needs.

The idea is to reduce the amount of water wasted during agricultural operations, especially irrigation. Paul Brierley, executive director of YCEDA, added that to figure that amount out, researchers studying the issue also have to consider how much water a crop needs to offset the effects of salinity in the water.

Convenience for ag water users is the endgame of the YCEDA’s 5-year study titled “Quantitative Assessment of Water and Salt Balance for Cropping Systems in Lower Colorado River Irrigation Districts.” Researchers like Brierley hope to use this study to create quick figures that tell agriculture water users exactly how much water they need for a crop with consideration to salinity and other variables.

Brierley said that the hope is to make those figures handy by putting it in an app for quick reference.

But the element that Brierley and YCEDA researchers are especially trying to emphasize is salt.

“The point of the project is to understand a crop’s exact water needs or exactly how much water specific crops use,” Brierley said. “Salinity is a big factor with the water we get here because it’s very salty water when it gets down here.”

Because water is always evaporating, which increases the concentration of salt in water, and always running over sediment, Brierley estimates that water that arrives in Yuma from the Colorado River has about 1,000 pounds of salt for every acre-foot of water, an acre-foot of water being enough water to cover an acre of land.

Water from the Colorado River adds salt to soil that can be damaging to crops, especially leafy greens, and, even worse, can ruin the soil.

“Salt can start building up in the soil, and what we were seeing before this study was that salt was starting to degrade the soil to the point of not being able to use it again,” said Dr. Mazin Saber, with YCEDA.

When the water leaves soil through evaporation, salt stays behind. By itself, salt harms plants, but water helps by pushing the salt downward, which is an effect called leaching.

“Part of what we’re looking at is how to handle additional water to keep the root zone of the crop moist,” Brierley said. “Whenever you get rain, it pushes the salt in the root zone downward, but because we don’t get much rain, you can also add water to keep salts out of the root zone.”

One of the figures that researchers with the YCEDA are looking for is an accurate “leaching factor,” which represents the portion of water that needs to be used to offset the effects of salinity in the water.

Leaching factors vary depending on a range of factors like crop type and season, but the main idea that YCEDA wants growers to know is that watering a crop should never account for a hundred percent of their water usage.

“The confusion is always that a hundred percent efficiency is the good thing, ‘I want a hundred percent efficiency,’ is what you’d naturally think,” he said. “But you need a hundred percent efficiency plus what you need to push down the salt.”

A grower can go maybe one to two years, Brierley said, using only the water they need for the crop. If they fail to account for the salt in the soil, the salt will cut off a root’s ability to take water from the soil and keep anything from growing in the soil, which will become dirt.

Brierley and YCEDA want the most crop productivity per water used.

“We want the most crop per drop,” Brierley said. Knowing what that is allows growers to be as conservative as possible while remaining efficient.

When the study began, YCEDA researchers had two of what are called Eddy Covariance machines, tripod-shaped equipment that measures factors around the crop to come up with the data used to make conclusion about leeching factors and water use. Within the 4 years, YCEDA has received five additional Eddy Covariance machines through contributions from organizations like NASA.

The University of Arizona started YCEDA as a public-private partnership with the goal of coming up with usable results for problems in Yuma agriculture. Supporters who have helped YCEDA pursue studies like the Quantitative Assessment include the US Bureau of Reclamation, NASA, and the US Department of Agriculture, and researchers who work with YCEDA come from a various of institutions and universities.

Brierley said that the underlying mission of this study is to come up with a long-term strategy for sustainable conservation practices in agriculture, which involves creating an understanding of how salinity affects soil and making that knowledge accessible for the future.

“I think we’ll be able to be more efficient with the amount of water needed once we make this information available,” Brierley said. “Water users have been pretty good about understanding what goes into water efficiency, and I think we’ll see that more with a generational transition in who’s using the farm and whose using the app we have in mind. Ag’s entering a new phase, and things will be more efficient.”

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