Minnesota’s fall nitrogen fertilizer restrictions in vulnerable groundwater areas take effect Sept. 1. The Minnesota Department of Agriculture (MDA) is reminding producers to confirm whether their fields fall within restricted zones and to monitor soil temperatures closely where fall application is allowed.
Under the Groundwater Protection Rule, fall nitrogen fertilizer application is prohibited in designated vulnerable areas. These areas—defined by coarse‑textured soils, shallow soils over bedrock, or karst geology—are more susceptible to nitrate loss and groundwater contamination. Producers can quickly determine whether a field is restricted by using the MDA’s online map.
In all other parts of the state where fall nitrogen application remains permitted, soil temperature is the key factor in reducing nitrogen losses. The MDA recommends waiting until the average soil temperature reaches 50 degrees or cooler before applying anhydrous ammonia, urea, or manure. Research shows that delaying fall application until soils cool improves nitrogen use efficiency, protects water quality, and increases the amount of nitrogen available for next season’s crop.
To support fall decision‑making, the MDA provides real‑time soil temperature data from 70 locations across Minnesota. The Six‑Inch Soil Temperature Network offers current 4‑ and 6‑inch soil temperatures and a week‑long history, making it easy to track cooling trends and determine when soils reach the 50‑degree threshold. University of Minnesota Extension provides the same temperature guidance for fall manure application to reduce leaching losses and protect groundwater.
“Minnesota farmers make careful decisions every fall, and nitrogen management is a key part of that,” said MDA Commissioner Thom Petersen. “Checking field status and waiting for soils to cool helps keep nitrogen where crops can use it and protects the groundwater our rural communities rely on. These steps support both long‑term productivity and water quality across the state.”
While many Minnesota fields fall outside the state’s vulnerable areas, good fall nitrogen management matters everywhere. Confirming whether fall nitrogen applications in fields are restricted—and waiting for 50‑degree soils where fall application is allowed—helps keep nitrogen in the crop zone and protects the groundwater rural communities rely on. Taking these steps supports long‑term productivity and ensures fall application aligns with agronomic best practices and state requirements.
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Media Contact
Cynthia Moothart, MDA Communications
651-420-2637
Cynthia.Moothart@state.mn.us
