Groundwater Management Questions

(From the Pierce Country water quality meetings.)

Elevated levels of nitrates have been found in water samples taken from irrigation wells in Pierce County. Several well samples have shown nitrate levels in the groundwater which exceed federal health limits of 10 parts per million (ppm).

How was this problem detected?

The Lower Elkhorn Natural Resources District (NRD), in cooperation with local irrigators, has been collecting groundwater samples from throughout the District for the past few years. The samples were analyzed by the Nebraska Department of Health Laboratories for nitrates.

How do nitrates reach the groundwater?

Agricultural fertilizers break down in the soil profile as nitrates. Nitrates are very soluble in water. When water from rainfall or irrigation passes through the soil and moves below plant root systems, any nitrate that is dissolved in the water can eventually reach the groundwater. This process is called leaching.

Why does this area have higher levels of nitrate?

Sandy soils, irrigation development and corn production have all contributed to the leaching of nitrates into the groundwater. Nitrogen fertilization is an economic necessity for growing corn in this area. Some of this nitrogen will be converted to nitrate; dissolve and move with water through the soil profile. The sandy soils in this area allows the water to move easily through the soil. Excessive moisture from either rain or irrigation can leach nitrates through the sandy soils--past the roots of the growing crop.

What is non-point contamination?

Simply stated, non-point pollution is anything that is not considered point source pollution. Point source pollution occurs in one specific point and can be attributed to such direct sources as underground fuel storage tanks or a chemigation tank back-siphoning.

Therefore, non-point source is pollution that moves through the soil and water that can not be determined from a specific point. Examples include: sediment runoff from the side of a hill, agricultural chemicals and fertilizers, and fertilizer runoff from lawns in town.

The high-nitrate problem in Pierce County is currently considered nonpoint source pollution. High concentrations of nitrates have been found in relatively large areas of the County.

How can this problem be solved?

It is important to understand that this problem was not created overnight. With community cooperation, reducing the levels of nitrates in the groundwater will take many years to correct.

Agriculture has an advantage over other industries in cleaning up pollution such as high levels of nitrate in the groundwater. Farmers may use the nitrates found in the groundwater through irrigation, allowing the crops to absorb the excessive nitrates. Farmers can use this problem to their advantage as a management tool.

What can I do as a farmer to reduce the nitrate levels?

As a farmer concerned about your family and the environment, you can implement best management practices (BMPs). BMPs include such things as setting realistic yield goals; testing for nitrate levels in irrigation water and soil samples; implementing UN-L Extension fertilizer recommendations; using irrigation water management; using split applications for fertilizer; using nitrogen inhibitors; and by not applying fertilizer in the fall.