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Chopped forage particle size analysis in one, two and three dimensions

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131620148,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Philippe Savoie, Marc-Antoine Audy-Dubé, Guillaume Pilon, René Morissette
Keywords:   particle sieving chopped forage image length

Abstract. Traditional particle size analysis of chopped forage is done by mechanical sieving, thereby providing mass distribution of one dimension. The ASABE standard method (S424.1) uses five sieves with square holes; it assumes a geometrical mean length for particles in each screen based on the diagonal of the screen and the diagonal of the screen above. Recent studies have shown that long and narrow particles can tip during shaking and slide through holes of diagonal length smaller than the longest particle dimension. When calibrated, image analysis is definitely more accurate in measuring true dimensions of chopped particles than screening. An experiment was carried out with chopped grass and corn harvested at three theoretical lengths of cut (TLOC = 3/16, 3/8 and 7/16 in., i.e. 4.8, 9.5 and 11.1 mm). Particles were initially sorted by the ASABE screening method. Particles within each screen were spread on a flat surface and photographed. Pictures were processed with Matlab software and an image analysis toolbox, providing total pixel area (linear resolution of 0.13 mm), the vectorial length (greatest distance between 2 points on the periphery) and an estimate of width for individual particles. All particles per picture were weighed, providing an estimate of average thickness. The ASABE standard method underestimated the true particle length measured by image analysis by an average of 31%. The average ratio of length to width was 4.0, and similar for both alfalfa and corn. The ratio of width to thickness averaged 20 to 1, but it varied more for corn (from 6 to 40) than for alfalfa (from 17 to 31). Image analysis provided detailed information on particle outer surface area per unit mass, with an average of 218 cm²/g DM (dry matter) for alfalfa particles and 139 cm²/g DM for corn particles. To improve measurement of forage particle length, width and thickness, mechanical screening could be used in combination with image analysis.

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