Submitted to: Cereal Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2003
Publication Date: 4/1/2004
Citation: Doehlert, D.C., Mcmullen, M.S., Jannink, J., Panigrahi, S., Gu, H., Riveland, N. 2004. Influence of oat kernel size and size distributions on test weight. Cereal Research Communications. Vol. 32:135-142
Interpretive Summary: Test weight is one of the most important characteristics for evaluating grain quality of oats. It is the bulk density of an oat sample, or the ratio of the grain mass to its volume. It is thought to be controlled by the actual density of the grain and a packing factor. The packing factor is reputed to be controlled by the size and shape of the grain and affects how efficiently grains of oats pack together. Frequently, grain cleaning operations will observe decreases in the test weight when the smallest kernels are removed. It could be hypothesized that small kernels fill in the spaces between the larger kernels as sand could fill in the spaces between pea gravel, allowing greater packing efficiency. To test this hypothesis, we separated oats into different size fractions with differently sized slotted sieves. We found that the combined volumes of the different size fractions usually did not significantly differ from the volume of the original sample. So genotypes did exhibit a difference, but when a difference was seen, the original sample packed less efficiently than the sum of its size fraction. Thus, we conclude that the packing effect is relatively minor, and decreases in test weigh with seed cleaning are due to the fact that smaller oat kernels are inherently more dense than the larger oat kernels.
Technical Abstract: Test weight is one of the most important characteristics for evaluating grain quality in oats. This study evaluated the role of oat kernel size and size distributions on test weight. Oat kernel size was measured from digital image analysis, sequential sieving and mean kernel mass on original oat samples and their different size fractions. Data from ten genotypes and eight environments indicated that smaller sized kernel fractions derived by sieving had higher bulk density than those from the larger sized kernel fraction. The smaller kernels also had greater groat percentages, indicating greater kernel density in smaller size fractions. To investigate a possible packing effect of different kernel sizes on test weight, the summation of volumes of size fractions was compared with the volume of the original sample. In many cultivars, there was no significant difference between these, but in genotypes with lower test weights, the sum of volumes of the fractions was significantly less than the volume of the original sample. This indicated that the more uniformly sized fractions packed more efficiently than the original sample. A similar experiment evaluating bulk densities of the size fractions reached the same conclusion. These results indicate that the test weight drops observed in seed cleaning, where the smaller kernels are removed, are due to the removal of the most dense kernels in the sample, and not to a packing effect, where smaller kernels might fill in spaces between larger kernels.