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The yield and quality of barley (Hordeum vulgare L.) are greatly influenced by N fertilization. The yield of dry matter, mineral nutrients, and protein are generally increased but the concentration of the essential amino acid lysine in the protein is usually decreased by increasing the supply of N. However, the effect of N may vary between genotypes. The purpose of this study was to compare the response to N of a high‐lysine genotype to that of normal barley. The high‐lysine Risø mutant 1508 and its parent variety ‘Bomi’ were grown in plastic pots containing 22 kg sandy loam (Gray‐Brown Podsolic soil). Nitrogen was supplied as NH4NO3 in amounts of: O, 1, 2, 3, 4, and 6 g N/pot. The yield of dry matter increased with N fertilization up to 3 to 4 g N/pot after which it declined with additional N‐supply, while the yield of protein continued to increase. Lower grain yield of the mutant was almost entirely caused by a smaller grain size. The concentration of lysine in Bomi protein declined when protein production was increased by application of N fertilizer, whereas in the mutant it remained nearly constant. The high‐lysine character was thus enhanced when protein content in the grain was increased. The concentrations of P, Ca, and Mg were higher while that of K was lower in the grain of the mutant 1508 than in the grain of the parent variety Bomi.

The Bomi and Sultan varieties have different co‐dominant alleles at one locus on chromosome 5 controlling the electrophoretic pattern of one group of hordeins. This locus is hypostatic to the recessive allele in Risø mutant 1508, which suppresses the formation of these and some other hordeins. The two loci appear to be unlinked.

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