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Home > Protecting Our Lands & Waters > Clean Water Fund > Groundwater & Drinking Water Protection > N Recs and WQ Impacts

Validating Nitrogen Recommendations and Water Quality Impacts under Irrigated Agriculture

The Minnesota Department of Agriculture is working with partners on two projects that will provide a better understanding of nitrogen fertilizer management and the associated water quality impacts on irrigated, sandy soils. One project is located in Westport, Minnesota at the Rosholt Farm and the other is located in Dakota County. 

The Rosholt Farm project is supported through a unique partnership between Pope and Stearns County Soil and Water Conservation Districts (SWCDs), Prairie Lakes Co-op, the University of Minnesota and the Minnesota Department of Agriculture. In Dakota County, partners include Dakota County Environmental Services and the University of Minnesota. 

The research design, treatments and questions are the same at both locations.

Project Goals:Lysimeters are an important research tool at the Rosholt Farm. Each white PVC pipe contains multiple sample lines.

  • Assess nitrogen loss resulting from different nitrogen fertilizer application rates, application timing, and application methods on sandy soils
  • Evaluate technology such as delayed release nitrogen products ESN and Super Urea
  • Evaluate in-season nitrogen sensing tools such as Greenseeker and Spad Meters
  • Provide critical data to help the University of Minnesota revise nitrogen fertilizer recommendations for irrigated coarse-textured (sandy) soils
  • Re-establish the Rosholt Farm as a local educational hub for local producers, agricultural dealers and crop consultants

On-Farm Research

These projects evaluate corn crop response and water quality impacts of different nitrogen practices in highly vulnerable irrigated settings.  Research sites feature three crop rotations; corn on corn, corn following soybeans, and soybeans following corn and evaluate various nitrogen products, rates and application times. Nitrogen rates range from 0–280 lbs. Plots are irrigated by a linear irrigation system at the Rosholt site and under a center pivot in Dakota County.

View a table of Nitrogen Rates and Treatments.

Water that escapes below the root zone of growing crops is analyzed for both volume and nitrate-nitrogen concentration. Soil water analyzed for nitrate-nitrogen concentration is collected in specialized equipment called "suction tube lysimeters" that are buried beneath the root zone throughout the study area. Soil water is pulled into the lysimeter through a ceramic tip that is under vacuum (pressure). Volume of soil water moving below the root zone is measured by drain gauges that are also buried in trenches below the surface so normal tillage and other farming operations can be performed.  

Follow this link to learn more about the Research Design at Rosholt Farm and Dakota County.  Research will be conducted during the 2011-2015 cropping seasons.

The suction tube lysimeters will remain undisturbed during the life of the project at Rosholt Farm. At the Dakota County site, the lysimeters are installed and removed annually to account for growing season losses. Samples are collected once per week during the entire cropping season (May-October) and after any significant rain event. Water samples are analyzed on-site using a Hach Ultraviolet Spectrophometer (see image bottom right). Additionally, researchers use high tech, in-field chlorophyll meters to measure plant nitrogen concentrations and provide information about plant nutrition during the growing season.Person pouring a water sample into a Hach Ultraviolet Spectrophometer for nitrate analysis

Lysimeter sample lines are enclosed in protective PVC pipe and buried in trenches below the surface so normal tillage and other farming operations can be performed.

At the Rosholt Farm, installation of field equipment began in 2010 and was completed in spring 2011. Sampling began in Dakota County in 2012. Results  will be posted on this webpage when they are available.

At Rosholt Farm, a weather station capable of measuring minimum and maximum daily temperatures, wind speed, relative humidity, solar radiation and rainfall has been installed. These measurements are used to calculate local evapotranspiration (ET) potential. Having a weather station on-site provides an accurate method of identifying crop water needs and helps eliminate under and/or over-watering. Access to information about local climate conditions enables crop producers to apply the right amount of water at the right time, minimizing the loss of water and nutrients.

Why is this project important?

Nitrate-nitrogen is a water soluble made up of nitrogen and oxygen. It can occur naturally in groundwater at levels typically in the range of 0 to 3 parts per million (ppm). Human activities such as sewage disposal, livestock production, and crop fertilization can elevate the level of nitrate in groundwater. The drinking water standard for nitrate is 10 ppm; above this level nitrate can have negative effects on human health, specifically infants under the age of six months. Nitrate has been found above the 10 ppm drinking water standard in Minnesota groundwater (specifically drinking water), mainly in areas where well construction or surface geology (type of bedrock or soil) allows for rapid movement of nitrate from the surface down to groundwater resources.

The University of Minnesota Nitrogen Fertilizer Recommendations specific to irrigated coarse-textured soils will be revised based on nitrogen rate, yield and potential leaching losses associated with the nitrogen treatments, allowing for new BMP development that keeps pace with the yield potential of new farm technology.

About Rosholt Farm

The Herman Rosholt Farm is located in Pope County near Westport, Minnesota. The farm's coarse-textured soils and need for supplemental irrigation typifies the challenges that many producers face on the outwash sands of west-central and central Minnesota. The farm is approximately 30 acres in size.

The Rosholt Farm is dedicated to agricultural research and education. Researchers focus on regional issues and agricultural practices that are typical in the area. Researchers address challenges that producers may face in the Central Sands region of Minnesota.

For more information about the history of Rosholt Farm, visit Pope County SWCD's website. 

The nitrogen rate studies are being conducted by Dr. John Lamb and Dr. Fabian Fernandez (University of Minnesota). Prairie Lakes Co-op provides agronomic services, irrigation scheduling and hosts real-time weather data, from MDA’s recently installed weather station. The Rosholt Farm  also hosts "Answer plots" and field days during the cropping season. At the Dakota County site, summer field days and winter crop days are hosted by the University of  Minnesota.

Please come visit!


  Pope County Soil & Water Conservation District logo Stearns County Soil & Water Conservation District logoUniversity of Minnesota logo  Prairie Lakes Coop logo

Dakota County logo Minnesota Department of Agriculture logo

 MDA Contacts

Dan Langseth
Fertilizer Management Adviser
Dan.Langseth@state.mn.us ~ 320-808-5834
Rosholt Farm

Ryan Lemickson
Fertilizer Management Adviser
Ryan.Lemickson@state.mn.us ~ 612-209-9181

Bruce Montgomery
Fertilizer Section Manager
 Bruce.Montgomery@state.mn.us ~ 651-201-6178