Anhydrous Ammonia - considerations for use

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Anhydrous ammonia is the most commonly used source of fertilizer applied N in Wisconsin. It's popularity stems from the fact that it is low cost and has a high nutrient concentration. However, there are some disadvantages to using anhydrous ammonia. Being a pressurized liquid, special handling and application equipment are needed. Additionally, extensive safety precautions need to be followed to avoid injury. Anhydrous ammonia has a great affinity for water and can injure the mucous linings of the nose, throat, and lungs if inhaled. The following is a summary of some considerations for anhydrous ammonia use and its effects on the soil.

Soil retention

Anhydrous ammonia is applied in oval or teardrop-shaped bands beneath the soil surface. Diffusion is more upward than down with the width of the band increasing as the rate increases. Most bands are 2 to 5 inches in diameter depending upon application rate, soil type, and soil moisture. Anhydrous ammonia reacts quickly with soil moisture to form ammonium cations which are held tightly to soil particles and are subject to little loss until converted to the nitrate form of N.

Loss of ammonia as a gas can be significant if proper application techniques are not followed or soil conditions are too dry or wet. The latter condition is a common problem on Fond du Lac County soils where pre-plant applications are made in the early spring. Too much soil moisture prevents the soil from sealing behind the applicator knives. Research shows that an application depth of at least six inches is needed to inhibit loss. Some type of knife slot-covering apparatus is also recommended.

Effects on microorganisms and soil properties

The high pH and nitrite concentration in the anhydrous ammonia band makes it toxic to soil microorganisms. Research on this topic shows microorganism numbers declining rapidly in the band shortly after application. However, populations rapidly increase within one week and are essentially the same as non-treated areas within five weeks after application. The negative effects on soil fungi is somewhat longer lasting than bacteria but still localized to the band and not considered to be permanent.

Anhydrous ammonia is often perceived to be detrimental to several physical and chemical soil properties. In fact, long term use of anhydrous ammonia has no impact on soil bulk density (a measure of compaction) or soil oraganic matter when compared to other N sources. All N sources tend to reduce soil pH over time.

Planting corn after anhydrous ammonia

There is no set recommendation as to how long a producer should wait between anhydrous ammonia application and corn planting. The criterion to avoid damage is not to place the seed in the retention zone. For this reason, careful monitoring of depth is critical. Application at an angle to corn rows is best. This will reduce the potential number of plants affected. Most of the diffusion of ammonia from the point of injection takes place within the first 24 hours. Ammonia should be injected 7 to 8 inches deep to minimize potential injury, especially if high rates of N are being applied.