A nitrification inhibitor is a chemical compound used to slow the nitrification of ammonia, ammonium-containing, or urea-containing fertilizers, which are applied to soil as fertilizers. These inhibitors can help reduce losses of nitrogen in the soil that would otherwise be used by crops.

For the purpose of these regulations, a nitrification inhibitor must include one of the following active ingredients Nitropyrin, Pronitridine, or Dicyandiamide. Requests for additions to the list of approved nitrification inhibitor active ingredients will be considered by the board upon request.

In Phase III management areas and Hastings Wellhead Protection Groundwater Management Area, if anhydrous ammonia is applied between November 1 and February 29, a district-approved, active ingredient containing, nitrification inhibitor must also be applied at the manufacturer’s recommended rate.  A receipt as proof of purchase for the nitrification inhibitor must accompany the producer's Phase II/III annual report.

Changes to District Rule 5 for setting the trigger levels in Phase II and Phase III management areas went into effect on February 1, 2013.  The Phase II trigger is 7 milligrams per liter (mg/l).  Zone 2 has a median groundwater nitrate level of 7.4 mg/l.  

Phase II producers are required to use electrical resistance blocks or capacitance probes to schedule irrigation in one field.  Scheduling irrigation using soil moisture information can reduce the risk of excess irrigation leaching nutrients from the root zone.  In a Phase II Management Area, producers are also required to take deep (24”) soil samples for residual nitrate in a corn field where corn will be planted again. It also requires producer training and annual reporting of management practices.

Increasing nitrates in groundwater have been a concern in the Upper Big Blue NRD for several years. Several communities in the District have found it necessary to construct new wells to comply with state and federal drinking water standards.  Some communities have built, or are considering, treatment plants.  Many rural residents have also replaced wells or installed private water treatment systems.

Nitrate is found naturally in the environment, however excess nitrates that are causing groundwater contamination come primarily from the use of commercial fertilizers.  Nitrogen fertilizer is needed to produce corn, however, the amount and timing of the fertilizer application can reduce the risks of groundwater contamination.  

Since 1996, the NRD has required that farmers wait until November 1st to apply anhydrous and to wait until March 1st to apply other formulations of nitrogen fertilizer.  In some parts of the District where groundwater nitrate is the highest, farmers are required by existing regulations to attend training classes, take soil samples, and calculate crop nitrogen needs.  Despite these efforts, groundwater nitrate levels have continued to rise.   

This Phase applies to the entire NRD. Anhydrous ammonia may not be applied for spring-planted row crops until November 1 each year. Other forms of nitrogen fertilizers may not be applied until March 1. (Exemptions: fertilizing of non-row crops such as wheat, rye, oats, pasture, etc.). The application of manure, municipal sludge or industrial waste must be in compliance with state regulations. The application of fertilizers when nitrogen is not the largest percentage of the formulation and the total nitrogen applied per acre is less than 25 lbs.  

This Phase applies to areas where the NRD has determined that the median groundwater nitrate level exceeds 7 parts per million. Requirements include: Phase I requirements continue; Producers must attend nutrient management training once every 4 years; Shallow and deep soil sampling to depths of 8 inches for nitrate and organic matter and 24 inches for residual nitrate is required for fields where corn or sorghum follow corn or sorghum; Electrical resistance blocks or capacitance probes used to measure soil moisture must to installed by each farm operator to schedule irrigation in at least one field; and, reports on fertilizer and irrigation management practices must be submitted annually.

This Phase applies to areas where the NRD has determined that the median ground-water nitrate level exceeds 10 parts per million. Currently, three Zones of the district are in Phase III management. Phase III Requirements include:  Phase I and II requirements continue; Soil sampling as described in Phase II must be done on a maximum of 40-acre grids; and, irrigation water sampling for nitrates is required; irrigation water from each active irrigation well must be tested once every three years for nitrates; and a district-approved nitrification inhibitor must be applied at the manufacturer’s recommended rate if nitrogen fertilizer is applied prior to March 1. N-Serve is the only district-approved nitrification inhibitor. 

• Rules and Regulations: Rule 5 Groundwater Management 
• Hastings Wellhead Protection Area Management Regulations
• Phase I/II/III Management Regulations