Factors contributing to varietal differences in the nutritive value of rice straw

The proportion in whole straw, chemical composition and in vitro dry matter digestibility (IVD) of the leaf blade, leaf sheath and stem (including inflorescence) fractions of 32 varieties of rice straw harvested from the same location, year and season, were measured. The composition and IVD of whole straw was then calculated. The mean proportion of blade, sheath and stem was 32.4%, 25.5% and 41.0%, respectively, in whole straw. Stem had a significantly higher IVD (58.9%), lower insoluble ash (6.9%) and lower total ash (18.9%) but a higher neutral detergent fibre (NDF, 62.7%) and lower crude protein (CP, 3.4%) than blade or sheath. For whole straw, the range in composition and IVD was: NDF, 54.2–63.2%; IVD, 44.4–64.7%; CP, 2.0–5.3%; insoluble ash, 6.2–14.4; total ash, 16.6–25.1%. cal correlation analysis showed that varietal differences in the composition and IVD of whole straw were significantly correlated (P < 0.001) with varietal differences in these parameters in the blade, sheath and stem fractions. Varietal differences in whole straw were not significantly correlated (P > 0.05) to their leaf, sheath and stem proportions or to their agronomic characteristics (culm height, days to maturity and grain yield). There is thus potential for breeding and selecting rice varieties with good straw and agronomic characteristics.