Edge-of-field monitoring conducted by the Discovery Farms Minnesota program can help identify connections between farming practices and environmental concerns. These water quality measurements can provide evidence of the effectiveness of the University of Minnesota’s nitrogen best management practices.

U-M’s nitrogen best management practices and recommendations are important for optimizing profits and protecting water quality, and they vary by region, soil type and crop type.

KNOW YOUR BMPs: Research and data from the University of Minnesota and Discovery Farms Minnesota show economic and environmental benefits from following best management practices for nitrogen.

Discovery Farms Minnesota has more than 25 site-years of surface and tile monitoring data at 12 privately owned farms throughout the state. Nitrate-nitrogen concentrations in surface runoff and tile drainage are a good measure of the effectiveness of nitrogen fertilizer management practices. Typical nitrate-nitrogen concentrations range from 1 to 3 mg/L in surface runoff and 15 to 25 mg/L in tile drainage.

Importance of incorporation

At a field in south-central Minnesota, measurement of nitrate-nitrogen in surface runoff in spring 2015 provided an example of the importance of good nitrogen application practices. For this field, urea had been broadcast to the soil surface of harvested soybean stubble in late November 2014, after the soil temperature had dropped below 50 degrees F. This is a suggested time for application in the fall. However, there was no incorporation in the fall as U-M’s BMPs for N use in south-central Minnesota recommend.

There was little breakdown of the urea after fall application to spring snowmelt, as nitrate-nitrogen concentrations were near the typical range during snowmelt in March. As soil temperatures warmed in the spring, the breakdown of the fall-broadcast urea accelerated.

A field cultivator pass prepared the seedbed for corn planting. However, this shallow incorporation still resulted in the nitrate-nitrogen produced from the breakdown of urea remaining close to the soil surface. Surface runoff caused by spring rains in May and June had greatly increased nitrate-nitrogen concentrations, resulting in potential economic loss for the farmer and potential environmental concerns.

Manure plus urea?

At a field in central Minnesota, measurement of nitrate-nitrogen in tile drainage in spring 2013 provided another example of the importance of good N management practices. The field had been in corn silage since 2010, with manure application every year. Nitrate-nitrogen concentrations in the tile drainage were near typical levels from 2010 to 2012. Manure was applied in fall 2012 for the corn silage crop the following year. In the spring, urea was also broadcast prior to planting. The urea application increased the rate of nitrogen application to well above recommended levels from U-M. Nitrate-nitrogen levels in the tile drainage also increased well above typical levels. A large portion of the applied nitrogen was lost through tile drainage that spring, resulting in potential economic loss for the farmer and potential environmental concerns.

When recommended best management practices are not followed, there could be loss of nitrate-nitrogen, with surface runoff and tile drainage leaving the field. Results from the Discovery Farms measurements confirm that these management practices are important and necessary to reduce both economic and environmental risk.

Source: Discovery Farms Minnesota