The drinking water standard for nitrate-nitrogen is 10 mg/L (ppm). From tile drainage research throughout the Corn Belt of the midwestern United States, even when nitrogen fertilizer is applied at economic optimum application rates to corn in a continuous corn or corn-soybean rotation, the nitrate concentrations in tile drainage commonly exceed 10 mg/L (ppm). So even when following recommended fertilization application rates, there can be a loss of nitrates to groundwater or surface water.

Consider the following recommendations to minimize nitrate loss:
• Apply nitrogen fertilizer at the appropriate rate.
• Avoid overapplication. (Follow local recommendations for nitrogen application rate.)
• Apply nitrogen fertilizer as close as possible to the time when the plant needs the nitrogen.
• Remember to credit nitrogen left over in the soil from the previous year's application or from manure or legume nitrogen releases.
• Consider using the Pre-Sidedress Nitrate Test (PSNT), if available in your state, to provide a check for insufficient, adequate or excess nitrates levels for crop growth.

Author: Matt Helmers, Iowa State University