Effects of genotype and simulated rainfall on the morphological characteristics, chemical composition and rumen degradation of the straw fractions of barley plants

Abstract

Experiments comparing the nutritive value of cereal straws from different genotypes are often complicated by the difference in plant height which is affected by genotype and the amount of rainfall. Two experiments were therefore conducted to study the morphological characteristics, chemical composition and rumen degradation of barley straw fractions from several genotypes over a range of watering levels. The range was obtained by using sprinklers to apply various levels of water in addition to normal rainfall. In Experiment 1, there were four genotypes of barley and three levels of watering, and in Experiment 2, another three genotypes of barley and four levels of watering. Grain and straw yield, stem height, the proportions of chaff, leaf and stem, the chemical composition of these morphological fractions, and the dry matter losses (DML) of fractions from nylon bags placed in the rumen, were determined. The extent and rate of DML was estimated. In both experiments, applying additional water almost doubled stem height. The effects of watering level on grain and straw yield and plant morphological fractions were therefore generally greater than the effects of genotype. In Experiment 1, genotype and watering level had few significant effects on the chemical composition of straw fractions and in Experiment 2 chaff composition was generally affected by genotype, but both genotype and watering level usually affected leaf composition. Both genotype and watering level affected the extent of digestion of leaf in Experiment 1, whereas in Experiment 2 genotype was more important than watering level in affecting the extent and rate of digestion of stem. The results show that water stress can affect the composition and rumen degradation of barley straw to a similar extent as can genotype. This finding should be recognised when comparing cereal straw from genotypes harvested in different years and locations in semi-arid environments.