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The literature available on the silica content of herbaceous biomass, and its relative mobility in leaching/extraction systems, includes studies that have employed several different methods for silica quantification. This makes comparison of the data difficult. The objective of this thesis research was to determine the quantitative relationships between the measured silica contents of biomass-relevant straws as determined by routine, published, silica quantification methods. Four representative straws were analyzed (wheat, Kentucky Bluegrass, Tall Fescue, and Perennial Ryegrass) using five methods. The methods included one gravimetric (G) and four colorimetric assays; the colorimetric assays differed with respect to the combination of digestion (two evaluated, D1 and D2) and color-development (two evaluated, C1 and C2) protocols. All of the methods tested were taken from the literature. The gravimetric method-determined silica contents of the straws were, in general, the highest. The exception being the values for tall fescue, for which all methods gave values that were not significantly different. All four of the colorimetric assays gave similar values for silica content, although in some cases these values were significantly different (P>0.05). The major difference in the colorimetric methods was found to be associated with the precision of the digestion protocols. A colorimetric assay, based on alkali digestion and subsequent reaction with ammonium molybdate for color development, was used to illustrate the potential of using moderately hot water (60 - 90°C) for the extraction of silica from wheat straw. |
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