Agriculture Reference
In-Depth Information
Table 3.3
Variation in CH
4
emissions with various
levels of submergence.
(Source: Wang et al.
1997b
)
Water depth (cm) % nodes submerged
CH
4
emission (%)
5.5
0
100
12.5
30
77
26.5
67
16
38
100
1
the role of aerenchyma of leaves, nodes and panicles in methane emissions. Emis-
sion through the rice plants is controlled by diffusion.
Wang et al. (
1997b
) reported that under various degree of submergence, the
emission rate gradually decreases and it completely stops under complete submer-
gence conditions. The study also proved that CH
4
emission through panicles is far
less than that of cracks and porous structure at nodes and increasing submergence
reduces CH
4
emissions temporarily until the concentration gradient is readjusted to
above water emission sites (Table
3.3
).
8.5 Cultivars Development
Das et al. (
2008
) studied methane emission in traditional cultivar 'Agni' and modern
improved cultivar 'Ranjit' under irrigated condition in North Bank Plain Zone of
Assam, India. They reported that Agni cultivar emitted more methane gas because
of its poor capacity for allocation of photosynthate to the developing grain, which
led to increased rhizo-deposition, thus increasing the CH
4
emission whereas 'Ranjit'
cultivar emitted less CH
4
it being able to allocate photosynthate efficiently towards
panicle and developing grains having smaller root length and smaller leaf area.
Wang et al. (
2000
) studied three rice cultivars and reported that IR65598 cultivar
had higher oxidative activity in the rhizosphere than IR72 and Chiyonishiki. They
studied the rate of CH
4
emission in different growth stages. In the tillering stage,
all the cultivars showed very low emission rate but at flowering and ripening stage,
IR72 and Chiyonishiki had significantly higher emission rate than IR65598. About
60-90 % of methane emitted from rice fields is transported through aerenchyma of
the rice plants (Holzapfel-Pschorn and Seiler 1986). Rice plants act as a conduit for
CH
4
emissions as well as source of methanogenic substrates. Yunsheng et al. (2008)
studied four cultivars (IR65598, IR72, Dular and Koshihikari) under elevated CO
2
concentration in Tsukuba, Japan, and reported that under elevated CO
2
conditions,
CH
4
fluxes increased by 10.9-23.8 % and daily CH
4
flux was highest for Dular and
lowest for Koshihikari. Mitra et al. (
1999
) studied six different rice varieties (Pusa
933, Pusa 169, Pusa 1029, Pusa Basmati, Pusa 677 and Pusa 834) in New Delhi and
reported that Pusa 933 emitted maximum CH
4
and Pusa 169 variety the minimum.
These studies show that use of different cultivars can be a good option for mitiga-
tion of CH
4
emission from the rice fields. They also provide clues that through '
on'
and/or '
Off
' the shelf techniques, new plant types could be developed with less
methane emitting potentials (Table
3.4
).
