Hd. Van Der Gon, Changes in CH4 emission from rice fields from 1960 to 1990s - 1. Impacts of modern rice technology, GLOBAL BIOG, 14(1), 2000, pp. 61-72
Four countries (Indonesia, Philippines, Thailand, and Nepal) were taken as
an example to assess the impact of changes in rice cultivation on methane e
missions from rice fields since the 1960s. The change of rice area by type
of culture from 1960-1990s is estimated, and its relative contribution to n
ational harvested rice area is calculated and multiplied with an emission f
actor, to derive the relative methane emission per unit rice land. Relative
methane emission per ha rice land has increased since 1960 for all four co
untries, largely due to an increase in irrigated rice area and partly due t
o a decrease in upland rice area. Patterns of rice area changes and related
emission changes differ considerably among countries. On the basis of the
rice area increases between 1960 and the 1990s, significant increases in me
thane emissions from rice fields due to increases in total rice cultivated
area are not to be expected in the future. The impact of modem rice variety
adoption is assessed by relating methane emissions to rice production. The
organic matter returned to the paddy soil is largely determined by rice bi
omass production which, given a certain yield, is different for traditional
and modern rice varieties. By calculating total organic matter returned to
rice paddy soils and assuming a constant fraction to be emitted as methane
, rice production and methane emission can be related. The analysis indicat
es that (1) up to now, rice yield increases in countries with high modem ri
ce variety adoption have not resulted in increased methane emissions per un
it of harvested area and, (2) global annual emission from rice fields may b
e considerably lower than generally assumed. The introduction of modem rice
varieties can be regarded as a historical methane emission mitigation stra
tegy because higher rice yields resulted in lower or equal methane emission
s.