NITROGEN-FERTILIZER AFFECTS AMINO-ACID-COMPOSITION AND QUALITY OF SPRING BARLEY-GRAIN

High N rates used to raise yields and the grain protein concentration (GPC) of cereal crops may lower the nutritional value of the grain by reducing the proportion of essential amino acids in the grain protein. Since spring barley (Hordeum vulgare L.) is an important feed grain for monogastric animals in eastern Canada, a 2-yr field experiment was conducted to determine N fertilization effects on the amino acid composition of the grain protein. Two cultivars, Leger (adapted feed type) and Argyle (unadapted malting type) were grown with four fertilizer treatments. The four fertilizer treatments were 0 or 100 kg N ha(-1) applied as ammonium nitrate at seeding, or with 100 kg N ha(-1) at seeding plus 50 kg N ha(-1) applied at awn emergence as broadcast ammonium nitrate (not included in 1988) or foliar-applied urea. Amino acid analyses were conducted by ion exchange chromatography. Nitrogen treatments increased protein per grain in both years, but increased GPC In 1988 only. In 1987, N treatments decreased the proportion of lysine in the grain protein but did not affect other amino acids. In 1988, increased N rates reduced the proportion of aspartic acid, threonine, glycine, lysine, and arginine but increased the proportion of glutamic acid and proline in grain protein. Higher N rates reduced the proportion of cyst(e)ine in grain protein in Leger only. Cultivar differences in amino acid composition were inconsistent between years. Higher rates of N fertilizer increased protein per grain and GPC but lowered the nutritional value of barley grain.