U.S. Water News Online
PUEBLO, Colo. -- Arkansas Valley farmers are dumping anywhere from 3 to nearly 10 tons of salt on their fields every year because their irrigation water is so salty, according to preliminary research by the U.S. Geological Survey.
That has prompted researchers to look into the potential effects of large municipal water projects that would take water from the Arkansas River. Some fear such projects could concentrate salinity and cause greater crop losses than area farmers are already experiencing.
The Arkansas River in Colorado and Kansas is the most saline river of its size in the country. Initial information from the USGS shows that salinity can increase by 61,000 percent from the headwaters near Leadville to the Colorado-Kansas border.
Average salinity ranges from 500 parts per million (ppm) of salts at Pueblo to 3,500 ppm at the state line. Agricultural crop losses can occur when levels climb above 700 ppm.
Decades of inefficient furrow irrigation, where the land is swamped with water, contributed to high salt levels that have cut crop yields since at least the 1970s. A study from that decade estimated the high concentrations were costing valley farmers millions of dollars a year.
Research by Colorado State University estimates that salts reduce yields by up to 20 percent across the valley, said civil engineering professor Tim Gates.
``What we are learning is that there is substantial promise for improving those conditions,'' he said.
Downstream from La Junta, almost all of the water in the river is from irrigation return flows, which builds greater salt concentrations over time. In 1900, wells near the Colorado-Kansas border had salt levels ranging from 291 to 962 ppm. Those same wells in 1940 measured from 2,800 to 4,600 ppm.
Besides crop losses, high salt levels can cause gastrointestinal distress in people and health problems in livestock and poultry.
``I believe there could be significant improvements,'' said Pat Edelmann of the U.S. Geological Survey.
Colorado State's research is examining ways that improved irrigation efficiency, canal lining canals, subsurface drains, groundwater pumping patterns and changes in river flows can reduce the salinity. The changes could boost farm yields, Gates said.
``Ultimately, the data and the modeling will provide tools to allow key decision-makers in the valley to come up with alternatives that will allow these problems to be mitigated and solved,'' he said.
Research at Colorado State's Arkansas Valley Research Center extension has demonstrated that drip irrigation can bring the same yields as furrow irrigation with one-sixth of the water for some crops, reducing the amount of salts flowing back into the river, said researcher Mike Bartolo.
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