Industry pros to lead irrigation workshops

- Spring 1999 "Update" Newsletter Article -

Subsurface on alfalfa

Dairy lagoon water will be delivered through drip lines

new application of subsurface drip irrigation (SDI) is being prepared for evaluation by the Center for Irrigation Technology (CIT). At a site near Fresno State’s dairy unit, a one-half-acre patch of alfalfa will be irrigated with water from the dairy’s waste water lagoon.

Since last fall when the alfalfa was planted, well water has been applied through conventional sprinklers to establish the stand. CIT researchers are nearly ready to begin using subsurface drip lines that were installed in 300-foot lengths about eight inches below the soil surface before the alfalfa was planted.

The private corporation funding the project believes the use of dairy waste water in subsurface irrigation will conserve water, avoid the problem of unwanted runoff, and reduce deep percolation of nitrates into the groundwater.

"The safe handling of lagoon waste water is of tremendous importance in California," commented CIT research engineer Ed Norum, who is overseeing the experiment. Use of lagoon waste water for flood irrigation of alfalfa and other crops is common in California, but the potential problems mentioned make subsurface an attractive option, he said.

Subsurface does have its own set of challenges, especially with water that can have high levels of particulates. "Obviously, there is a problem you have to solve; you have to have the water soluble enough to run through the system," Norum said.

In most dairy operations, the waste water collected from cleaning around the stalls is pumped through a large, above- ground separator that filters out much of the solid material and dumps it in piles for drying. The remaining water is pumped into one or more lagoons. While that water serves for flood irrigation, a filter system capable of handling high levels of fiber and other solid materials is needed for subsurface application, Norum said.

A conventional screen filter for this project already has proved ineffective because of plugging problems. A sand media filter that can be cleaned more effectively will be tried next.

Irrigation system hardware also includes a computerized programmable logic controller which will be used to control irrigation and for record-keeping. The controller is at the pump site and can be operated by radio communication. The water from the lagoon is nutrient rich; also high in nitrates. Once all hardware components are functioning efficiently, then testing to determine the nutrient levels of the alfalfa will begin, Norum said.

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