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Irrigation - Frequently Asked Questions

What does it cost to setup a new quarter-section center pivot?

A new center pivot irrigation system needs a water source (well or surface water), a pump, a power source (electric motor or engine), controls and often a buried pipeline. At 2013 prices, the average cost of a new quarter section center pivot (irrigating about 128 acres of the 160 acres), setup in a field with a concrete pad, is about $80,000. The cost of the pump, well, pipeline, controls and power may add another $60,000 for a total investment around $140,000 or near $1,100 per irrigated acre. More information on getting into irrigation can be found in these online publications: http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae92.pdf and http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae91.pdf

Does chlorinating an irrigation well every year do any good?

Irrigation wells tap aquifers and unfortunately, most aquifers in North Dakota contain some level of dissolved iron. The amount of iron may vary from low to high but its presence in the water leaves a rusty color on pumps, pipelines and irrigation systems. The iron in the water provides energy to iron bacteria that leave a slimy organic substance on well screens, pump intakes and other parts of the well. It only takes a few years for this organic substance to plug the well screen and reduce well production. The only way to control iron bacteria is by annual chlorination. More information can be found in this online publication: http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae97.pdf

What are the important parameters I should look at in an irrigation water quality report?

Most irrigation water analysis reports will provide a list of cations (calcium, magnesium, sodium and potassium) and anions (bicarbonate, carbonate, sulfate and chloride) along with pH, total dissolved solids (TDS), electrical conductivity (EC) and the sodium adsorption ratio (SAR). The cations, anions and TDS have units of milligrams per liter (mg/l)

The two most important factors are TDS or EC and SAR. The TDS of a water sample is a measure of the concentration of soluble salts in the water, which include all the cations and anions. TDS is estimated from the EC of the water. The more dissolved minerals in the water, the higher the EC. The units of EC can be listed as millimhos per centimeter (mmhos/cm), micromhos per centimeter (umhos/cm) or deciSiemens per meter (dS/m). One millimho per centimeter is equal to 1000 micromhos per centimeter or 1 dS/m. TDS can be estimated by multiplying the EC (in umhos/cm) by 0.64. For example, the TDS of a water sample with an EC of 2000 umhos/cm (2.0 dS/m) would be about 1280 mg/l.

The SAR of a water sample is the proportion of sodium to calcium and magnesium in the water. Since it is a ratio, SAR has no units. For most soils in North Dakota, any water with an EC greater than 2000 micromhos per centimeter (2 mmhos/cm or 2 dS/m) or an SAR value greater than 6 is not recommended for continuous irrigation. More information can be found in this online publication: http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae1675.pdf

Can all soils be irrigated?

All soils can be irrigated but the right irrigation system has to be selected. For example, soils with a high clay content can be irrigated with a trickle (often called drip) irrigation system, a surface irrigation system (if the land has less than 2% slope) and a solid-set sprinkler system, however, a moving sprinkler system like center pivots and lateral moves may not work very well. Conversely, a soil with a high sand fraction on sloping land can be irrigated very well with a moving sprinkler system but not by a surface irrigation system and it may be difficult to use trickle irrigation and solid-set sprinklers due to elevation differences.

Center pivots are used to apply water to over 85% of the irrigated land in North Dakota. Due to the preference for moving sprinkler systems, all the soils in the state have been classified as irrigable, conditional and non-irrigable. The irrigable and non-irrigable classifications are self-explanatory but a soil may be conditional for one or more of the following reasons: salinity accumulation concerns, too much slope, irrigation water quality, shallow bedrock, poor drainage characteristics and too much gravel.

Successful irrigation also relies on the compatibility of the water quality with the soils in the field. In general, sandy well-drained soils can be irrigated using water with higher TDS and SAR than soils with more clay and silt content. Information on soil/water compatibility can be found in this online publication: http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae1637.pdf

Soil irrigability classification has also been incorporated into the North Dakota State Water Commission (SWC) GIS based water information system. An irrigation compatibility layer is part of the map service portion of the SWC found at this website: http://mapservice.swc.nd.gov/. Click on the “Show Layers” tab on the right side of the map to turn on the irrigation compatibility layer.

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