Best Management Practices for Nitrogen Use
in East-Central and Central Minnesota

Copyright ©  2002  Regents of the University of Minnesota. All rights reserved.

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Nitrogen (N) is an essential plant nutrient that contributes greatly to the agricultural economy of Minnesota crop producers. Unfortunately, the nitrate form of nitrogen can leach into surface- and groundwaters if nitrogen management is not practiced carefully. The public will not tolerate contamination of water resources by agricultural production systems; laws regulating use of nitrogen fertilizers could be adopted if contamination from agricultural activities is not minimized.

The research-based Best Management Practices (BMPs) outlined in this bulletin are economically and environmentally sound. It is strongly suggested that farmers adopt them voluntarily. By following these recommendations, agriculture can avoid the threat of fertilizer regulations and enjoy a more profitable and better community.

Introduction

Nitrogen (N) is an essential plant nutrient that is applied to Minnesota crops in greater quantity than any other fertilizer. In addition, vast quantities of nitrogen are contained in the ecosystem, including in soil organic matter. Biological processes that convert nitrogen to its mobile form, nitrate (NO₃), occur continuously in the soil system. (For greater detail see Understanding Nitrogen in Soils FO-3770.) Unfortunately, nitrates can be leached from the rooting part of the soil. To minimize losses to surface- and groundwater, management guidelines have been developed.

Best Management Practices (BMPs) for nitrogen are broadly defined as "economically sound, voluntary practices that are capable of minimizing nutrient contamination of surface- and groundwater." The BMPs recommended here are based upon research, particularly at the University of Minnesota and other land-grant universities, and upon practical considerations.

The BMPs are based, in part, upon the concept of total nitrogen management, which accounts for all forms of on-farm nitrogen in the development of crop management plans. BMPs were developed to be adopted on a statewide as well as a regional basis. Those developed for east-central and central Minnesota refine the recommendations of the statewide BMPs.

Statewide Nitrogen BMPs

Statewide BMPs are applicable to all crops and farming practices. They are based upon the concept that accurate determination of crop nitrogen needs is essential for profitable and environmentally sound nitrogen management decisions. The statewide BMPs shown below are described in greater detail in Best Management Practices for Nitrogen Use Statewide in Minnesota FO-6125.

• Set realistic yield goals.

• Develop and use a comprehensive record-keeping system for field-specific information.

• Adjust nitrogen rate according to soil organic matter content, previous crop and manure applications.

• Use a soil nitrate test where appropriate.

• Use prudent manure management to optimize nitrogen credit.
  • Test manure for nutrient content.
  • Calibrate manure application equipment.
  • Apply manure uniformly throughout a field.
  • Injection of manure is preferable, especially on strongly sloping soils.
  • Avoid manure application to sloping, frozen soils.
  • Incorporate broadcast applications whenever possible.

• Credit second-year nitrogen contributions from alfalfa and manure.

• Do not apply nitrogen above recommended rates.

• Plan nitrogen application timing to achieve high efficiency of nitrogen use.

BMPs for East-Central and Central Minnesota

East-central and central Minnesota are characterized by coarse- to medium-textured soils. Most soils in the region were formed in glacial till, with some outwash plains also common. Most east-central and central Minnesota soils are moderately to excessively drained. While most soils in this region are susceptible to leaching, relative differences must be assessed based on soil texture, rainfall, and subsoil.

Average annual precipitation in the region is 25 to 30 inches. Crops are dominated by corn and forages. Specific BMPs for these regions, which include the counties of Cook, Lake, St. Louis, Carlton, Aitkin, Itasca, Isanti, Koochiching, Lake of the Woods, Cass, Beltrami, Hubbard, Wadena, Crow Wing, Morrison, Benton, Stearns, Todd, Mille Lacs, Becker, Otter Tail, Kanabec, Pine, Chisago, Anoka, Sherburne, Ramsey, Hennepin, Wright, and Washington (Figure 1), have been based on field research in Minnesota as well as field research conducted on similar soils in the Midwest.

Figure 1. Thirty-county area of east-central and central Minnesota for specific BMPs for nitrogen.

Nitrogen BMPs for east-central and central Minnesota include:

• Carefully manage nitrogen applications on soils characterized by a high leaching potential.

1. Do not apply fertilizer nitrogen in the fall to coarse-textured (sandy) soils.

Coarse-textured soils are present in counties throughout east-central and central Minnesota. (For irrigated coarse-textured soils, refer to the bulletin Best Management Practices for Nitrogen Use on Irrigated and Coarse-Textured Soils FO-6131.) It is extremely important to practice high-level management of nitrogen on these soils for environmental and agronomic reasons. Fall-applied nitrogen, because of the delay between application and crop need, has a greater risk of nitrifying and leaching out of the rooting zone.

Figure 2 illustrates the differential yield response that time of nitrogen application produced when 78 pounds of nitrogen per acre (lb N/A), as urea, was applied to non-irrigated, coarse-textured soil.

Figure 2. Three-year corn grain average yields as affected by fall, spring and early summer nitrogen applications. (Schmitt and Beck, 1991)

2. When soils have a high leaching potential, application of nitrogen in a sidedress or split application program is preferred. Use a nitrification inhibitor with early sidedressed nitrogen on labeled crops.

Data obtained in a three-year study on a coarse-textured, irrigated soil at Becker indicate a clear advantage for sidedress and split applications of nitrogen compared to a single preplant application (Table 1). Under these conditions, corn yields were increased by adding a nitrification inhibitor (nitrapyrin) to the sidedress and split applications of nitrogen at rates up through 150 lb N/A.

• Spring preplant application of anhydrous ammonia or urea is encouraged. Broadcast urea should be incorporated within three days of application.

With soils that do not have a high leaching potential, using preplant nitrogen fertilizer in the ammonium-N form instead of nitrate-N (mobile) form reduces the immediate potential for nitrogen leaching loss. Under normal spring conditions, anhydrous ammonia and urea will take from two to six weeks to nitrify from the ammonium form to nitrate. This delay decreases the potential for leaching of nitrate during the last part of April and in May, when precipitation is highest and crop demand for nitrogen and water is very low.

Urea broadcast on the surface should be mixed into the soil (incorporated) soon after application to reduce potential loss by volatilization and surface runoff. Volatilization is generally accelerated by crop residue and high soil pH. Although high soil pH is uncommon in east-central and central Minnesota, high amounts of surface residue are more common because of conservation tillage being used with continuous corn. In addition, urea left on the soil surface can easily be washed toward streams and lakes during intense rains.

• Inject or incorporate sidedress applications of urea and UAN to a minimum depth of 4 inches.

Incorporation of urea and urea-containing fertilizers reduces the potential for loss by volatilization. In addition, materials injected or incorporated to a 4-inch depth are more likely to reach roots under dry conditions. Surface-applied materials are less likely to reach roots under dry conditions, and yields may suffer.

Nitrogen not absorbed by plants often remains in the soil after harvest and thus is highly susceptible to leaching loss before the next year's crop can use it.

Related Publications

FO-6125 Best Management Practices for Nitrogen Use Statewide in Minnesota

FO-6126 Best Management Practices for Nitrogen Use in Southeastern Minnesota

FO-6127 Best Management Practices for Nitrogen Use in South-Central Minnesota

FO-6128 Best Management Practices for Nitrogen Use in Southwestern and West-Central Minnesota

FO-6130 Best Management Practices for Nitrogen Use in Northwestern Minnesota

FO-6131 Best Management Practices for Nitrogen Use on Irrigated, Coarse-Textured Soils

FO-5883 Self-Assessment Worksheets for Manure Management Plans

FO-3790 Fertilizing Corn in Minnesota

FO-3813 Fertilizing Soybeans in Minnesota

FO-3814 Fertilizing Alfalfa in Minnesota

FO-3773 Fertilizing Barley in Minnesota

FO-3772 Fertilizing Wheat in Minnesota

FO-3770 Understanding Nitrogen in Soils

FO-3774 Nitrification Inhibitors and Use in Minnesota

FO-3769 Providing Proper N Credit for Legumes

FO-2392 Managing Nitrogen for Corn Production on Irrigated Sandy Soils

FO-0636 Fertilizer Urea

FO-3073 Using Anhydrous Ammonia in Minnesota

FO-6074 Fertilizer Management for Corn Planted in Ridge-till or No-till Systems

FO-3553 Manure Management in Minnesota

M. A. Schmitt
Extension Specialist
Department of Soil, Water and Climate
University of Minnesota

G. W. Randall
Soil Scientist
Southern Experiment Station
University of Minnesota

Funding for this publication was by the U.S. Department of Agriculture, Extension Service, under project number 91-EWQI-1-9265.

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