Mineral Fertilizer Use and the Environment International Fertilizer Industry Association United Nations Environment Programme

8.1. Ammonia
H. Kirchmann (1998) observed that ammonia
deposition from the atmosphere may enrich
terrestrial and aquatic ecosystems. On average in
West Europe 92% of all ammonia originates
from agriculture. About 30% of the nitrogen
excreted by farm animals is released to the
atmosphere from animal houses, during storage,
grazing and application of animal wastes to the
soil. Ammonia emissions from growing arable
crops are low, but emissions can be higher from
decomposing crops. Composting results in high
ammonia losses.
Deposition of ammonia takes place over areas
where lower amounts would have been supplied.
This deposition together with that from nitrogen
oxides decreases biodiversity, but it can increase
carbon storage in sediments and forest soils. Near
very large animal farms, local toxic effects
damaging the surrounding vegetation can occur.
Ammonia deposition contributes to
acidification of soils as ammonia is nitrified to
nitrate and then nitrate is lost by leaching.

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Mineral Fertilizer Use and the Environment
matter releases carbon dioxide back to the
atmosphere. Good fertilization and tillage
management practices improve the net gain of
carbon to the soil.
Recent estimates indicate that agricultural and
forested land in the Northern Hemisphere is now
a net sink for carbon dioxide from the
soil/plant complex due to increased vegetative
growth. According to E. Solberg (1998), for every
pound of nitrogen applied as fertilizer,
10 to 12 pounds of carbon can be sequestered.
The rapidly increasing use of reduced tillage
systems is helping to rebuild soil organic matter,
hence increasing the quantity of carbon stored.
8.2.2. Nitrous oxide
Nitrous oxide has a greenhouse effect and is
considered to be detrimental to the ozone layer.
According to experts of the Intergovernmental
Panel on Climate Change (IPCC), nitrous oxide is
responsible for 7.5% of the calculated greenhouse
effect caused by human activity. Its concentration
in the atmosphere is increasing at a rate of about
0.2% per annum. Soils are the major global
source of N
2
O accounting for some 65% of all
emissions; they are the result of microbial
processes. Nitrogen fertilizers can be a direct and
indirect source of N
2
O emissions; IPCC currently
assume an N
2
O emission factor of 1.25% of
fertilizer N applied, but with a nine-fold range,
from 0.25% to 2.25%. In general, fertilizer
management strategies that increase the
efficiency of N uptake by crops are likely to
reduce emission of N
2
O to the atmosphere. For
further information, refer to O.C. Bockman and
H.-W. Olfs (1998) and K.A. Smith et al. (1997).