Managing irrigation can increase yields

By Tom Hintgen (Contact) | The Daily Journal

Published 12:00 p.m., August 2, 2007

Even with irrigation use during extreme heat such as what Otter Tail County experienced in July, one of the most difficult parts of irrigation management is how much water to apply. Fortunately, irrigation scheduling methods are available from the East Otter Tail County Soil and Water District Office in Perham.

“Using rational or scientific methods to schedule irrigations is essential for good irrigation management,” Irrigation Scheduler Technician Arnie Rethemeier said.

Good irrigation management, Rethemeier said, begins with accurate measurement of the rain received on each irrigated field and knowing the soil moisture status in each field at the start of the vegetative growth stage.

“Measurement of soil moisture levels has been the most common method of irrigation scheduling, but newer methods use a combination of crop water use and soil water estimates,” Rethemeier said.

More accurate soil moisture measurement methods use mechanical devices such as tensiometers and soil moisture blocks for irrigation scheduling. Other more sophisticated instrumentation can be used for irrigation scheduling but generally are not used for irrigation management because of the expense.

An irrigation scheduling procedure called the checkbook method has been used successfully for many years in western Minnesota and eastern North Dakota. This program was developed by North Dakota State University and modified by the University of Minnesota.

“The checkbook method is a soil moisture accounting method which uses crop water use (evapotranspiration rate) values and soil water holding capacities to predict the time to irrigate and amount of water needed to replenish what has been removed from the root zone,” Rethemeier said.

Each day the computer program subtracts the daily evapotranspiration for the specific crop from the pervious day from the current moisture content of the soil. If rain or irrigation water is added to the soil, that is added to the moisture content of the soil.

“This provides the field operator with the information needed to make decisions about application of irrigation,” Rethemeier said.

The East Otter Tail Soil and Water Conservation Service operates a weather station housed at the Perham Airport that provides information such as high and low temperature, humidity, wind speed and direction, daily solar radiation, and crop potential evapotranspiration rate. There are web sites available to the land operator to provide the estimated evapotranspiration rate for each specific area that the land operator is irrigating.

The goal of the program is twofold. The first is to prevent soil water depletion that could result in lower crop yield. A second purpose that is equally important is to monitor the soil moisture level so that excess irrigation water is not applied that could result in washing of nutrients into the water table.

In 2007, the East Otter Tail Soil and Water Conservation Service has 29 area farm operators participating in the irrigation management program that includes 118) fields and approximately 11,000 acres. The irrigation technician checks each field on a weekly basis to evaluate the soil moisture content to compare results with the Checkbook Program.

Results of U.S. Geological Survey water-quality studies provide water managers with essential information needed to make ground-water management decisions throughout Minnesota.

State regulatory agencies are using results of USGS studies to develop new agricultural best management practices for farmers to reduce stream and ground-water contamination. The USGS works closely with state and local agencies.

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