Barley

Barley is the fourth most cultivated cereal in the world. Worldwide, barley is predominately grown as feed grain and also for malting to produce alcoholic beverages. Barley straw is used for animal bedding in developed countries and for animal feeding, especially in developing countries. Most projections calculate that cereal production has to increase 50% or even more in the next 50 years to meet the growing demand; therefore the understanding of processes determining development, growth, and yield in cereals, including barley, is relevant for crop breeding and agronomy. Two botanical types of barley can be distinguished, two- and six-row genotypes. Six-row barley tends to have higher grain protein concentration than two-row barley, which is generally better suited for animal feed; however, both types are suited for malting when management practices are adjusted. Traditionally, two-row malting barley has been grown in Europe, Australia, and South America, whilst six-row malting barley has been more commonly cultivated in North America. This chapter describes the physiology of crop development and environmental factors affecting the duration of vegetative and reproductive phases when different yield components are established. In barley, the ‘critical period’ occurs immediately before heading when the most relevant numerical and physiological yield components are determined. Grain number, which is the yield component more closely associated with yield, depends more on the survival than on the initiation of structures that may potentially produce a grain. In two-row barley, spikes per unit area is more important than grains per spike to determine grains number, while in six-row barley, both spikes per unit area and grains per spike are important. Because nutrition and water availability are crucial for yield and grain quality in different environments, this chapter presents impacts of limitations in a few nutrients, focusing mainly on nitrogen (N), because it is generally the most important nutrient in terms of deficiencies in production systems around the world. N limitations reduce yield and grain quality but, excess N is also a problem in malting barley, because high grain protein content is an undesirable trait for the brewing industry. We outline the implications of climate change for breeding and crop management because warmer temperature potentially shortens the crop cycle duration, reduces the capacity of the crop to capture radiation for photosynthesis, reduces yield, and alters grain quality. In this chapter, we synthesise knowledge on barley crop physiology and agronomy with a focus on malting barley.