R. Wassmann et al., Mechanisms of crop management impact on methane emissions from rice fieldsin Los Banos, Philippines, NUTR CYCL A, 58(1-3), 2000, pp. 107-119
This article comprises 4 yr of field experiments on methane (CH4) emissions
from rice fields conducted at Los Banos, Philippines. The experimental lay
out allowed automated measurements of CH4 emissions as affected by water re
gime, soil amendments (mineral and organic), and cultivars. In addition to
emission records over 24 h, ebullition and dissolved CH4 in soil solution w
ere recorded in weekly intervals. Emission rates varied in a very wide rang
e from 5 to 634 kg CH4 ha(-1), depending on season and crop management. In
the 1994 and 1996 experiments, field drying at midtillering reduced CH4 emi
ssions by 15-80% as compared with continuous flooding, without a significan
t effect on grain yield. The net impact of midtillering drainage was dimini
shed when (i) rainfall was strong during the drainage period and (ii) emiss
ions were suppressed by very low levels of organic substrate in the soil. F
ive cultivars were tested in the 1995 dry and wet season. The cultivar IR72
gave higher CH4 emissions than the other cultivars including the new plant
type (IR65597) with an enhanced yield potential. Incorporation of rice str
aw into the soil resulted in an early peak of CH4 emission rates. About 66%
of the total seasonal emission from rice straw-treated plots was emitted d
uring the vegetative stage. Methane fluxes generated from the application o
f straw were 34 times higher than those generated with the use of urea. App
lication of green manure (Sesbania rostrata) gave only threefold increase i
n emission as compared with urea-treated plots. Application of ammonium sul
fate significantly reduced seasonal emission as compared with urea applicat
ion. Correlation between emissions and combined dissolved CH4 concentration
s (from 0 to 20 cm) gave a significant R-2 of 0.95 (urea + rice straw), and
0.93 (urea + Sesbania), whereas correlation with dissolved CH4 in the inor
ganically fertilized soils was inconsistent. A highly significant correlati
on (R-2 =0.93) existed between emission and ebullition from plots treated w
ith rice straw. These findings may stimulate further development of diagnos
tic tools for easy and reliable determination of CH4 emission potentials un
der different crop management practices.