With the increase in emissions linked to human activity, ammonia gas has become one of the main causes of soil acidification, even though it is originally a natural process.
Ammonia, a natural product
Ammonia is a natural gas produced during the conversion of the urea in organic products into ammonium ion under the effect of microorganisms. It is the synthesis of an enzyme, urease, by these bacteria and yeasts that generates this production.
This volatilisation of ammonia into the air occurs more or less quickly depending on the soil pH (slower in acid soil) and the temperature. The higher the temperature (summer, tropical climate) the higher the production of ammonia.
Ammonia production is therefore originally a natural process.
Ammonia production and man-made emissions
Other than the chemical industry, particularly fertiliser manufacture, the intensification of agricultural production methods lies at the source of most ammonia emissions.
Indeed, the extensive use of chemical fertilisers containing nitrogen, first and foremost urea, releases ammonia through volatilisation during the conversion to nitrate. Given that urea is the most widely used nitrogen-based mineral solution worldwide, this gas release concerns all continents. Gas emission levels reach those of industrialised countries in tropical countries with wet conditions and high temperatures.
The other agricultural source of this ammonia emission is intensive farming. The decomposition of urine and excrement generates ammonia regardless of the species farmed. In addition to the strong odour, ammonia can become toxic if high concentrations are inhaled when working in this type of livestock farming.
Other than agriculture, waste treatment at plants is another source of these emissions into the air.
Atmospheric ammonia, source of acidification
After its nitrous form, ammonia gas is the main source of nitrogen in the air. Composed of 3 hydrogen atoms, the atmospheric emissions of nitrogen increase the acidity level of rainwater. When it rains, this hydrogen concentration (H+) increases soil acidity and its liquid solution causing an increased risk of erosion, surface sealing and pollution, and lower agricultural yields.
To combat these risks, short-term solutions rely on the use of more fertiliser, more chemicals against pests and therefore more ammonia emissions… But there is an alternative solution.
Reducing ammonia emissions through different forms of nitrogen
Safeguarding water, the environment and soil fertility requires the use of non-chemical practices.
Limiting tillage encourages the development of filamentous fungi and therefore the conversion of organic matter into humus, thus increasing the soil’s capacity to store water, nitrogen and carbon.
The introduction of leguminous plants in rotations, capable of fixing nitrogen from the air and restoring it to succeeding crops, is one way to limit the consumption of chemical forms of mineral nitrogen by farms and to increase their autonomy.
It can be assumed that these examples of solutions, which are part of a wider set of eco-fertilisation practices, will have a positive impact on soil fertility, environmental protection and above all food security by increasing agricultural productivity.
