Scientist studies quality of tailwater used for irrigation

Frances Gould, McClure, Olivia J.  |  10/14/2016 6:18:42 PM

Summer weather brought severe seasonal drought conditions to many farms in Louisiana this year, highlighting the need for farmers to find dependable sources of irrigation water to meet crop needs during critical stages of growth.

Changyoon Jeong, a water quality specialist at the LSU AgCenter Red River Research Station, is studying options for Louisiana farmers, including tailwater recovery systems that capture water that runs off the field and can be reused for irrigation. While useful in some cases, these systems can also promote greater nutrient losses and salt accumulation depending on the soil type, Jeong said.

Some of Jeong’s work has focused on the Natural Resources Conservation Services’ Red Bayou Watershed Project in the Shreveport area. The project pumps water from the Red River into Red Bayou, giving farmers in northwestern Louisiana access to surface water they can use for irrigation instead of putting further pressure on the area’s declining aquifer.

“However, the quality of the tailwater from the Red Bayou has not been fully tested for use as irrigation water in soybean production,” Jeong said.

Jeong has been monitoring the quality of water from Red Bayou used for irrigation. Salinity in water is influenced by season, weather conditions and the presence of agriculture activities, he said.

He took soil samples from two soybean fields — one with sandy soil, the other with clay soil — at the beginning of the 2016 crop season to measure nutrient levels.

As the irrigation water moves down the slope of the field, so do salt and nutrients. In samples taken from the field with sandy soil, Jeong found that electrical conductivity — which indicates salinity — increased as he moved from the top of the field toward the field’s low point. In clay soil, electrical conductivity decreased moving down the field’s slope, but carbon and nitrogen increased, he said.

Soil pH increased along the slope of the clay soil field after irrigation, but pH was higher at the beginning of the slope in the field with sandy soil.

“Research data showed that higher nutrient losses in sandy soils and more salinity accumulation in clay soils can be caused by tailwater irrigation,” Jeong said.

Nutrient leaching through the soil profile is another concern when irrigating, Jeong said. In tests, he found that nitrate concentrations rose with increasing depths in sandy soil. Nitrate accumulated at shallower depths in clay soil. Soluble, reactive phosphorus showed significant downward movement in both soil types, he said. Olivia McClure

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