When soils are too dry, anhydrous ammonia (NH₃) cannot react with soil water to form stable ammonium (NH₄⁺), which can increase the risk of volatilization losses, crop injury, and uneven nitrogen distribution.
Anhydrous ammonia must be injected below the soil surface where it reacts instantly with water to form NH₄⁺, which binds to the negatively charged soil. If this reaction can’t happen due to lack of soil moisture, then the NH₃ gas can escape. “The nose knows.” If you smell ammonia 24 hours after the application in that field you are having N loss.
Losses are typically greatest in:
- Dry, coarse-textured soils (sands, loamy sands)
- Dry, heavy clays with large cracks or poor knife closure
- Fields tilled too coarsely, leaving large air gaps in the injection path
Even a small percentage of loss can add up quickly. A 10% loss of 180 lb-N rate equals 18 lbs of N lost per acre. Roughly, $11 per acre at $0.60/lb N.
If we continue to experience dry weather into the spring other risks include ammonia burn to seed/roots if band is placed too shallow or too close to the row. Uneven nitrogen distribution can also occur if ammonia gas moved in the soil before stabilizing.
Management Strategies
Check soil moisture at injection depth
Grab a handful of soil from 6–8 inches. If it crumbles into dust, it’s too dry to seal well. If it forms a weak ball when squeezed, it’s likely adequate.
Use correct depth and spacing
Go deeper (7–8 inches) in coarse soils and maintain spacing to ensure soil closure. High-speed application increases loss risk in dry conditions.
Consider timing & tillage
If soil is too dry, consider delaying application until after rainfall improves moisture conditions. Tillage after an application can open further pathways for loss. Delay tillage until soil has received moisture and ammonia odor is gone.
Use a nitrification inhibitor
Adding a nitrification inhibitor, like N-Serve and Centuro, can further slow the conversation of NH₄⁺, to NO3-, protecting N through the winter and early spring.
Supporting articles
Fall Anhydrous Ammonia Applications: What to know about soil moisture — Iowa State Crops Extension
Anhydrous Ammonia Application in Dry Soil — Iowa State Univ. Extension / Integrated Crop Management