The application of nitrogen fertilizer on cropland in the fall or on frozen soils will be restricted in vulnerable groundwater areas. This includes quarter-sections of land where 50 percent or more of the quarter-section is in an area with vulnerable groundwater and in DWSMAs that have nitrate-nitrogen concentrations at or in excess of 5.4 mg/L nitrate-nitrogen.
An area with vulnerable groundwater is an area where nitrate can move easily through soil and into groundwater, contaminating drinking water sources. Some portions of the DWSMAs have low and very low vulnerability, those areas are not subject to the fall restriction. Vulnerable areas for Part 1 of the rule are defined as:
- coarse textured soils based on USDA NRCS soils maps
- shallow bedrock based on USDA NRCS soils maps; or
- karst geology based on MN DNR map.
Areas within a DWSMA which are low risk to groundwater contamination in the Minnesota Department of Health Wellhead Protection Plan are exempt from fall application restrictions.
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