Arkansas Valley: Lysimeter installations producing useful data

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Here’s an update on Colorado State University’s lysimeter installation in the Arkansas Valley, from Chris Woodka writing for the Pueblo Chieftain. From the article:

The devices are capable of measuring small changes in water on blocks of soil that will help determine how much water crops in the Arkansas Valley are using. That could help Colorado in its ongoing dispute with Kansas over how much water each state is entitled to under a 1948 compact as well as give farmers better information about how and when to irrigate. “We’re trying the best we can to measure consumptive use and account for all the factors that go into the equation,” said Lane Simmons, a research associate.

So far, there are not concrete results, although farmers who have toured the site are already optimistic that the research will prove what they instinctively believe – that Colorado has never gotten enough credit for its water use. Mike Bartolo, director of the research center, is careful to put the brakes on jumping to any conclusions. “It’s premature to make any conclusions,” Bartolo said. “We have one year of data and we don’t fully understand the dynamics. . . . After three or four years, we’ll have a clear picture of what’s happening with alfalfa.”

There are two lysimeters at the research center, which is about one mile east of Rocky Ford. The larger one, completed in 2007, weighs changes in a 10-feet by 10-feet cube of soil 8 feet deep. On a hot summer day, when evaporation is at its peak, there might be a change of 150 pounds in the 50-ton block. Scales connected to computers record the slightest change.

The smaller one is a reference lysimeter in a nearby field that is 5-feet by 5-feet and 8 feet deep. “It’s built for precision,” Simmons said, following a line on the computer in his office. “You can see it level off at night, then it goes down during the day, levels off again and spikes when there’s an irrigation.”[…]

To see the lysimeter itself, requires going through a metal hatch down a ladder in a 12-foot hole in the ground. The lysimeter sits on the sensitive scales, but there are also barrels to catch water as it makes its way through the soil and an array of tubes that can either vacuum water out or inject water into the sample…

Water comes into the cube either by precipitation or irrigation. It leaves through evaporation, transpiration (through growing plants) or seepage. By combining the weather data and the weight of the soil block, researchers can account for every drop. The scales can measure the changes day-in and day-out all year long…

The state is funding the research partly through a legal defense fund set up during the 1986 U.S. Supreme Court case filed by Kansas over the Arkansas River Compact. During the case, a special master sided with Kansas on the use of the Penman-Montieth equation in determining crop use. Rather than a simple mathematical formula, it uses actual crop data to determine consumptive use by plants. The problem is there is no hard data available for Colorado. The closest lysimeters are in Texas and Idaho, so the numbers in the equations now being used are only a good guess…

The data also can be used to calculate better numbers for crops other than alfalfa, which is used as the reference point in the model and is also the predominant crop in the Arkansas Valley. The numbers also are helpful in an ongoing study led by Colorado State University professor Tim Gates on salinity and water tables in the Arkansas Valley. “The evapotranspiration values of crops can have direct consequences to irrigation scheduling, water augmentation plans, interstate compacts and other farm management plans,” Simmons explained. “More accurate determinations of ET values can lead to gained efficiencies in water use and irrigation management.”

More Coyote Gulch coverage here.

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