An irrigation demonstration was held at the city of Paynesville's pretreatment plant on County Road 33 next to an irrigated field owned by Art Voss on Thursday, Aug. 5. The demonstration was sponsored by the Stearns County Soil and Water Conservation District.Steve Sellnow, Stearns County NRCS, led off the discussion by talking about the wellhead protection program of which the city of Paynesville is a member.
Sellnow explained that the land around Paynesville is a gravel outwash plain. The purpose of the wellhead protection program is to protect the underground aquifer. "The city has done a good job managing its delicate system as they use effluents to irrigate the land and yet not pollute the aquifer under the land," he said.
"There are several farmers outside the wellhead area involved in the program," Sellnow added.
"Because of the type of soil in the area, it is important not to over irrigate the land," Sellnow said. "One of the best methods is the feel/appearance method which involves collecting soil samples in the rot zone with a soil probe or a spade. The soil water depletion of each sample can be estimated by feeling the soil and comparing its appearance to tables established by the extension service."
Sellnow informed those present that crops on irrigated land using effluents cannot be fed to humans, only to animals.
Jerry Wright from the University of Minnesota talked about irrigation scheduling and calibration methods.
Wright said fields need a good balance between water loss, ground infiltration, and plant transpiration. "The top two inches of soil moisture content is where most of the evaporation takes place," he added.
In talking about irrigating with effluents, Wright mentioned that there are high concentrates of nitrogen in the water. "This nitrogen will never be eliminated," he added
"We don't encourage over application of water. Under ideal conditions, six to seven inches of water per acre per irrigation season is needed in addition to the normal rainfall," he said. An irrigation season is considered May to October.
"Corn needs five to seven inches of water per irrigation season to mature from milk stage to maturity. This amount will depend on the type of soil. The lighter the soil, more water will be needed. A corn plant will be in stress several days before you start seeing the stress," Wright said. "Corn doesn't like temperatures in the 90s. Once temperatures hit 90, the plants start to shut down.
Two to five percent of the water in an irrigation system is lost to evaporation. The amount varies with the humidity and wind conditions, Wright cautioned.
Wright urged the farmers to walk their fields, checking moisture conditions throughout the growing season.
Another speaker was Ron Mergen, Paynesville Public Works Director. He explained the city's lagoon system and the arrangement the city has with the farmers.
"The city started with eight center pivots and two traveling guns in 1985. Today, they provide water to 11 center pivots which irrigates 1,100 acres," Mergen said.
The city lagoons encompass 165 acres which contain 215 million gallons of water. From that, the city pumps seven inches of water per acre per irrigation season onto irrigated land.
"In the early years, we did not have enough land to spread the water over, especially in the wet years. To get rid of the water, we pumped an excess amount onto the fields. We had no place else to go. Then the city purchased 360 acres of CRP/grazing land. Now the city has the means of getting rid of the water and aren't forced to push the excess onto the farmer's fields," Mergen said.
This summer, the city has pumped about five inches of water per acre onto the fields. The city has the capacity of pumping 6,500 gallons per minute.
"During the dry years, the CRP and grazing land doesn't receive any water through the irrigation system. All the water is directed to the cropland," Mergen said.
One farmer asked how much nitrogen was in the water. Mergen replied one and a half to two pounds per acre per inch of water.
The city also has a tile system which brings the excess subsurface water on the fields to a retention pond. The retention pond covers eight acres and is about 20 feet deep on the south side.