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

8.2.3. Methane (CH
4
)
Methane production mainly stems from wetlands,
paddy fields, gastric fermentation within
ruminant animals, animal wastes, domestic
sewage and abiotic sources such as coal mining
and natural gases etc. The direct impact of
chemical fertilizers on methane emission is not
clear.
In the USA it is estimated that agricultural
sources account for 29% of US methane
emissions. Of the agricultural emissions ruminant
animals account for 62%, animal waste for 32%
and rice paddies for 5%. There are indications
that cultivation and N fertilization decreases the
rate at which CH
4
is taken up from the
atmosphere by soils, thus contributing towards
atmospheric methane levels, but the amounts
involved are small relative to total sources.
(W. Griffith and T. Bruulsema, 1997).
A. Suzuki (1997) reports that rice paddy fields in
Japan are thought to account for about 10% to
30% of total methane emissions from all sources.
In rice paddies methane is formed by the
anaerobic decomposition of organic matter. The
addition of readily decomposable organic matter
significantly increases methane emissions.

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Mineral Fertilizer Use and the Environment
23
9. Nutrient losses and efficiency
Data from Rothamsted Experimental Station
in the UK for phosphorus, show that from 1843
to until the 1970s, the overall P offtake was about
a third of that applied, similar to Finck’s data. But
with today’s yield of 8.5 t/ha grain, the P offtake
in grain plus straw is almost equal to the annual
application, of 35 kg P/ha, although not
necessarily from the P applied for that particular
crop. Similarly the increased yield of winter
wheat now removes in grain plus straw most of
the K applied each year (90 kg K/ha).