Morphological fractions, chemical compositions and in vitro gas production of rice straw from wild and brittle culm1 variety harvested at different growth stages

The comparison was made between wild and gene mutant variety brittle culm1 (bc1) rice straw harvested at four different growth stages in terms of morphological proportion, chemical composition and in vitro gas production. Both varieties were harvested on day 73, 95 (anthesis), 105, and 116 (physiological maturity) of growth post-sowing, designated as Cut 1, Cut 2, Cut 3 and Cut 4, respectively. During the growing stage, the bc1 variety had significantly higher proportion of stem, but lower proportion of leaf blade than the wild. The rice straw and straw fractions for bc1 variety were significantly lower in acid detergent fiber and ash contents, and higher in lignin (pm) and crude protein contents than those for wild variety. The bc1 rice straw was significantly higher in gas production rate, but lower in potential gas production and lag time than the wild, with little varietal difference in organic matter digestibility between two varieties. With the increasing harvest date, the lignin (pm) content increased, while the crude protein content decreased for both rice straw. No drastic variation was showed on gas production and organic matter digestibility of rice straw near physiological maturity from Cut 3 to Cut 4. The neutral detergent fiber and silica insoluble in acid detergent and neutral detergent were lower for stem than those for the other fractions. The gas production and estimated organic matter digestibility of the stem were significantly higher than those of other straw fractions. The result indicated that the gene mutant led to a reduction in gas production and an increase in gas production rate. The physiological maturity stage was optimal harvesting time for both grain and straw production.