The Minnesota Department of Agriculture is working with partners at the Rosholt Farm in Westport, Minnesota to provide a better understanding of nitrogen fertilizer management and the associated water quality impacts on irrigated, sandy soils. 

Research at this site provided, in part, the basis for the University of Minnesota's 2015 recommendations outlined in Fertilizing Corn Grown on Irrigated Sandy Soils (University of Minnesota website, PDF).

 Current Research

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. In 2011 and 2016, the MDA and partners began data collection for two studies.

1. Nitrogen and Water Quality Research

GOAL: To evaluate the management of nitrogen fertilizers and cover crops in irrigated crop production and their impacts to groundwater resources.

The study evaluates the impact of a living mulch (kura clover) and cover crop (winter rye) or no cover crop on nitrate leaching and nitrogen management on irrigated row crops.

Rosholt Farm Nitrogen and Water Quality Research Fact Sheet (PDF)

2. Reduced Irrigation Study A

GOAL: To improve irrigation water use efficiency by better understanding the interaction of water requirements of corn and plant population.

The study evaluates the grain yield impact and corn rooting depth when reducing the frequency of irrigation. The study will also determine the role of reduced plant population under reduced irrigation frequency to optimize grain productivity. 

Rosholt Farm Reduced Irrigation Study Fact Sheet (PDF)

Completed Research


The research that led to the University of Minnesota's 2015 recommendations outlined in Fertilizing Corn Grown on Irrigated Sandy Soils (PDF) was done in conjunction with a project near Hastings, Minnesota in Dakota County during the 2011-2015 cropping seasons.

The research design, treatments and questions were the same at both the Rosholt Farm and Dakota County location. The following were accomplished: 

  • Assessed nitrogen loss resulting from different nitrogen fertilizer application rates, application timing, and application methods on sandy soils
  • Evaluated technology such as delayed release nitrogen products ESN and Super Urea
  • Evaluated in-season nitrogen sensing tools such as Greenseeker and Spad Meters
  • Provided critical data to help the University of Minnesota revise nitrogen fertilizer recommendations for irrigated coarse-textured (sandy) soils
  • Re-established the Rosholt Farm as an educational hub for local producers, agricultural dealers and crop consultants
  • Installed water sampling equipment and a weather station at Rosholt Farm that will be available for future research

Research Design, Sampling and Weather Data

Importance of Understanding Nitrate

Nitrate-nitrogen is a water soluble compound made up of nitrogen and oxygen. It can occur naturally in groundwater at low levels. Human activities such as sewage disposal, livestock production, and crop fertilization can elevate the level of nitrate in groundwater. The health risk limit (HRL) 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 HRL 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 Guidelines (PDF) specific to irrigated coarse-textured soils were revised based on nitrogen rate, yield and potential leaching losses associated with the nitrogen treatments, allowing for new best management practice development that keeps pace with the yield potential of new farm technology.

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). CHS Prairie Lakes provides agronomic services and irrigation scheduling. Pope Soil and Water Conservation District posts real time weather data from MDA’s weather station. The Rosholt Farm also hosts field days during the cropping season.



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