Ammonia emissions from mineral fertylisers and fertylised crops

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Abstract:

A thorough understanding of the physical and chemical processes involved in NH3 emission from inorganic N fertilizers and fertilized crops is required
if reliable and operational NH3 emission factors and decision support systems for inorganic fertilizers are to be developed, taking into account the actual
soil properties, climatic conditions and management factors. For this reason, the present review focuses on processes involved in NH3 volatilization from
inorganic nitrogen fertilizers and the exchange of ammonia between crop foliage and the atmosphere. The proportion of nitrogen lost from N fertilizers due to NH3 volatilization may range from <0 to .50%, depending on fertilizer type, environmental conditions (temperature, wind speed, rain), and soil properties (calcium
content, cation exchange capacity, acidity). The risk for high NH3 losses may be reduced by proper management strategies including, e.g., incorporation of
the fertilizer into the soil, use of acidic fertilizers on calcareous soils, use of fertilizers with a high content of carbonate-precipitating cations, split
applications to rice paddies or application to the soil surface beneath the crop canopy. The latter takes advantage of the relatively low wind speed
within well-developed canopies, reducing the rate of vertical NH3 transport and increasing foliar NH3 absorption. Conversely, NH3 is emitted from
the leaves when the internal NH3 concentration is higher than that in the ambient atmosphere as may often be the case, particularly during periods
with rapid N absorption by the roots or during senescence induced N-remobilization from leaves. Between 1 and 4% of shoot N may be lost in this way.