Agriculture Reference
In-Depth Information
Fig. 3.3
Methane production
potential of one-day exudates
of Dular, IR72 and IR65598
cultivars at seedling stage
(SL), panicle initiation (PI),
flowering (FL) and maturity
(MT). (Source: Aulakh et al.
2001
)
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Their study suggested that CH
4
emission was more strongly related to total or-
ganic C (
r
= 0.920) than that of organic acids (
r
= 0.868). Rice root exudates act as
a substrate for the methanogenic bacteria in anoxic condition. The study also sug-
gested that for cultivation of high-yielding varieties (e.g., IR65598, IR65600) could
reduce CH
4
emissions as they produce lowest exudate-induced CH
4
production.
Thus, selection of rice cultivars could reduce CH
4
emission in regional and global
level.
Various studies have reported about increment of root exudation due to lower
membrane permeability and root porosity caused by P deficiency (Ratnayake et al.
1978
; Graham et al.
1981
; Lipton et al.
1987
; Kirk and Du
1997
). Low P could
stimulate the downward transfer of oxygen and upward transfer of methane due to
increased root porosity (Justine and Armstrong
1987
; Kludze et al.
1993
). P defi-
ciency stimulates a chain of reactions that affect the partitioning of photosynthates
and lead to higher root/shoot ratio (Marschner
1996
; Kirk and Du
1997
). Lu et al.
(
1999
) reported that low P supply to rice plants resulted in significant increase in
CH
4
emissions (34-50 micromoles under P deficiency and 10-22 micromoles under
ample P supply), increase of root/shoot ratio by factors of 1.4-1.9, better develop-
ment of root aerenchyma and increase in root exudation by factors of 1.3-1.8.
8.7 Methane Transport Capacity
Aulakh et al. (
2000a
) have studied methane transport capacity (MTC) of rice plants.
They have reported that up to the concentration level of 7500 ppm, methane trans-
port by rice plant increases linearly with increasing CH
4
concentration in the nutri-
ent culture solution surrounding the roots. Their study also reported that MTC of
IR72 was lowest at seedling stage (average 8 mg CH
4
/plant
-1
/day
-1
), then increases
gradually until panicle initiation (maximum, 120 mg CH
4
/plant
−1
/day
-1
) and after
that it gets reduced significantly at maturity (Fig.
3.3
).
Thus, cultivation of rice varieties having low MTC can reduce methane emis-
sions from rice fields (Butterbach-Bahl et al.
1997
). Aulakh et al. (
2000b
) estimated
