AmmoniakVolatilisation

AmmoniakVolatilisation refers to the loss of ammonia (NH3) to the atmosphere from agricultural systems, primarily after the application of nitrogen fertilizers or manure. The process occurs when ammonium (NH4+) present in the soil, or produced from urea hydrolysis, is converted to gaseous ammonia that diffuses into the air. This volatilization is influenced by chemical reactions in the soil, temperature, moisture, pH, wind speed, and surface conditions.

In soils, urea-based fertilizers are rapidly hydrolyzed by the enzyme urease, producing ammonium and carbonate and often raising the pH in the localized layer. Higher pH and warmer temperatures increase the proportion of NH3 relative to NH4+, promoting volatilization. Surface-applied fertilizers or manures on dry or loose soils, and during periods with little plant cover or slow incorporation, are especially prone to losses. Moisture status, including wind-driven loss from exposed surface residues, also plays a key role.

Environmental and agronomic impacts include the direct loss of plant-available nitrogen, reduced fertilizer efficiency, and positive feedback to atmospheric chemistry. Ammonia volatilization contributes to local air quality concerns and can deposit back as airborne nitrogen, affecting acidification and eutrophication in ecosystems.

Mitigation strategies focus on reducing the time ammonia remains in the surface layer and enhancing incorporation. Methods include timely incorporation or rapid incorporation of fertilizers, using urease inhibitors to slow urea hydrolysis, selecting fertilizer formulations with lower volatilization risk, timing applications to cooler or more humid periods, and maintaining crop residues or physical barriers to reduce surface contact. Proper storage of manures and careful handling also help limit volatilization losses.