Theoretical and Empirical Relationships Between Oat Test Weight and Groat Proportion

Cereal Chem. 86(2):239–246 Test weight and groat proportion are two very important quality characteristics of oat grain. In this study, we pose the hypothesis that these two characteristics are related through characteristics of grain density. Test weight is defined as the product of kernel density and packing proportion. Groat proportion, in theory, is the ratio of the groat mass to the kernel mass. We present two theoretical constructions expressing test weight in terms of groat proportion, packing proportion and kernel density components. To test these, we have applied measurements of test weight, groat proportion, kernel density components, and packing proportion of 18 oat cultivars grown at six environments. Whereas the groat proportion alone accounted for only 34% of the variation in test weight, our theoretical constructions that included groat proportion could account for ≤82% of variation in test weight. Also, we present previously undescribed variation in oat kernel density components across genotypes and environments. Although the kernel density alone could account for most of the variation in test weight across genotypes, packing proportion appeared to be more important in describing variation in test weight of a genotype across different environments. We observed significant variation in both groat and hull density which, together with groat proportion, described most of the variation in kernel density. Test weight, or bulk density, is the mass of grain that fits into a specified volume. It is often considered to be one of the most important measures of grain quality (Stoa 1922; Sword 1949; Lea 1955; Hoffmann and Livezey 1987; Forsberg and Reeves 1992). It constitutes a characteristic of major importance in grain grading (USDA 1988) and remains an important characteristic considered in commercial grain purchases (Ganssmann and Vorwerch 1995), although historically its value has been disputed (Grieg and Findlay 1907; Zavitz 1927; Sword 1949; Peek and Poehlman 1949). It can be described as the product of mean kernel density and packing proportion (Hlynka and Bushuk 1959; Yamazaki and Briggle 1969; Doehlert and McMullen 2008)