EFFECT OF RICE STRAW APPLICATION ON CH4 EMISSION FROM PADDY FIELDS .2. CONTRIBUTION OF ORGANIC-CONSTITUENTS IN RICE STRAW

Contribution of organic constituents in rice straw (RS) to the increase of the CH4 emission rates from paddy fields was estimated in a pot experiment. The same amounts of RS in which lipid, water-soluble polysaccharide, and hemicellulose fractions were successively removed were applied to the submerged paddy soil. Methane emission rates were markedly different among the treatments in the early period of growth of the rice plant. The removal of lipids and lipids plus water-soluble polysaccharides from RS increased the total (H-1, emission by 36 and 46% during the first 48-d period after transplanting, respectively. The additional removal of hemicellulose decreased the total CH4 emission by 23% during the same period compared with the treatment applied with original RS. On the other hand, the CH4 emission rates in the subsequent growth stages were similar among the treatments. Based on the difference in the CH4 emission among the treatments and the relative content of each organic constituent in RS, hemicellulose was estimated to contribute most significantly to the CH4 emission from paddy fields treated with rice straw in the early period of plant growth.