Ammonia can be converted to nitrate for plant uptake, while some plants may use ammonia directly. Use of ammonia for plant fertilization is well known and predictable. Mineralization occurs when the soil is not frozen. A problem can arise when organic N is mineralized in the spring and fall when soils are unfrozen, but minimal plant growth is occurring. Mineralized N can be converted to nitrate and leached from the soil when plants are unable to take it up, contributing to ground water pollution.
Ammonia availability is a predictable fertilizer, whereas organic N availability is unpredictable.
The higher the percentage of N in the ammonia form, the less uncontrolled release of N from organic compounds to the soil. To maximize the benefit of manure fertilization and minimize leaching losses, ammonia is preferred. In the cooler regions of the US, heated tank digesters may substitute for the treatment volume of a lagoon at a cost near the cost normally invested in that volume. However, a digester does not replace the need for storage. Lagoons are used to biologically stabilize and minimize odors from manure.