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Irrigated dairy pasture soil water profile research project

Vince Crary

Published in Dairy Star June 20, 2008

Pasture irrigation shows promise for dairy
and beef producers in Central Minnesota.
V. Crary

A University of Minnesota research project to study the feasibility of installing pasture irrigation on dairy farms was conducted in Wadena County during the summers of 2006 and 2007. The project took place on the Dan and Rosie Middendorf farm of Verndale. The research was conducted by Extension Engineer Jerry Wright, Agricultural Business Management Regional Extension Educator Margot Rudstrom and Otter Tail County Extension Educator Vince Crary. Douglas County Extension Educator Larry Zilliox put together the final report and fact sheet. Funding for the project was provided thru the U of M Central Regional Partnership of Staples and the Central Minnesota Irrigators Corporation. This article will discuss the project and results.

The soil type under the irrigator consisted primarily of Forada Loam, Verndale sandy loam and Blowers sandy loam soil. It has a water holding capacity of low to medium. Top soil depth is 6-9 inches with subsoil consisting of coarse gravel.

The irrigation equipment consisted of a center pivot system. Moisture conditions were monitored by the use of watermark soil moisture devices placed at 4, 8, and 12 inch depths.

Supplemental irrigation of field crops in central Minnesota on especially drought sandy textured soils is considered a best management practice if an adequate water supply is available. For most crops the recommendation has been that an irrigation sprinkler system should have an available pumping water supply of 5 to 6 gallons per minute per acre of land to be irrigated, if one can operate 24 hours per day during extended droughty periods. During mid-June to mid-August irrigated corn can use over 0.25 inch of water per day under clear skies and normal temperatures. Irrigated pasture during this same time period will only use around 75 to 80 percent of that used for corn. Hence, a water supply for irrigated pasture can be 20 to 25% less (4 to 5 gallons per minute per acre) if no additional downtime is expected each day during the peak water use period for pasture growth.

To maintain adequate soil moisture in a pasture, the irrigator operator should regularly check the soil profile in the top 12 to 18 inches with a soil probe or keep track of the estimated daily crop water use rate. Some type of soil water sensors such as tensiometers could also be used. It is generally recommended that an irrigation application should be initiated before the soil moisture in the upper soil profile becomes 50 percent depleted.

Irrigated corn in central Minnesota typically requires around 18 inches of soil water per growing season under normal weather conditions plus about 9 to 10 inches of irrigation water per season. Irrigated pasture has a similar soil water requirement between the beginning of May and the end of September. However, its monthly usage is generally 1 to 2 inches higher in the months of May and September, and 1.5 to 2 inches less than corn in the months of July and August.

This pasture irrigation research was designed to help livestock producers answer the question, "could irrigation be added to a pasture and would it be profitable to do so?" The grazing seasons of 2006 and 2007 proved to be good summers to conduct the research as both growing seasons were very dry. The research project proved to be of interest to a lot of livestock producers (both dairy and beef) in central Minnesota.

As a result of the research project and tours, four area dairy producers and one beef producer have now installed various styles of pasture irrigation systems. We also have knowledge of a number of other livestock producers in Otter Tail and surrounding counties that are studying the feasibility of installing pasture irrigation on their farms.

We held two project tours that were very well attended where participants visited the irrigated pasture sites. We conducted four winter meetings early this year. Three of the dairy producers using pasture irrigation, including Dan Middendorf, talked about their systems. The results of the pasture irrigation project research were also highlighted. The tours and meetings were very successful in getting the information to the producers.

Each growing season is different and presents various challenges to livestock producers. With water being the most important nutrient for both plants and animals, livestock producers who depend on pasture for grazing can ensure this nutrient will be adequately available thru the use of some form of irrigation system.

Based on the results obtained through this research project, pastures grazed properly and using a well managed pasture irrigation system can provide excellent returns to livestock producers.

A fact sheet on this research project is being put together and will be available in the future. For further information regarding this research, contact Vince Crary at 218-385-5420 or by email.

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