Nitrogen Credits for Soil & Water

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Agricultural Best Management Practices

Nitrogen Credits for Soil & Water

Farmers can sometimes use less fertilizer to raise a corn crop if they take advantage of other nitrogen sources available to the crop, such as residual nitrate in soil and irrigation water. Here’s how to calculate the amount of nitrogen corn can obtain from soil and irrigation water, based on University of Nebraska recommendations: 

  • Soil: An estimated one-third of cropped fields contain enough residual nitrate to justify applying less fertilizer. Taking soil samples is the only reliable way to find out. Soil samples should be collected from a minimum depth of 3 feet (4 feet is recommended). Each sample should represent no more than 40 acres (20 acres or less if possible). Please have the soil samples laboratory tested. The fertilizer nitrogen requirement for a crop is reduced by 8 lb/acre for each part per million residual soil nitrate-nitrogen.
  • Water: Collect a sample during irrigation season after the well has been pumped for at least 24 hours. Containers are available from county extension offices or testing laboratories. The laboratory will report the nitrate concentration in parts per million (ppm) or milligrams per liter (mg/l), which are the same. Multiply this number by 2.72 to get the pounds of nitrogen per acre applied with each foot of irrigation water. For example, water that contains ten ppm of nitrate would provide 27.2 pounds of nitrogen per acre for each foot of water applied. This amount can reduce fertilizers. For more information and graphs, Click Here.

Additional Information

Contact the Cooperative Extension or USDA Natural Resources Conservation Service for more details and information.

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