Seasonal trends in herbage yield and quality of Agropyrons

Crested wheatgrasses (Agropyron spp.) are grown on 6 million ha in the U.S. and Canada, where they provide excellent early-season forage, but lose nutritional quality by midsummer. Some producers believe that A. fragile maintains its quality longer than other crested wheatgrasses. This study compared herbage yield and quality of 3 A. fragile entries with A. desertorum, A. cristatum, 1-28 (induced tetraploid of A. cristatum), and the hybrid 'Hycrest'. Entries were established near Logan, Ut., on 1-m spacings. Herbage yield and quality were determined in year 2 and 3 at vegetative, boot, flower, seed ripe, and post-seed-ripe maturity stages (harvests 1 through 5) and on regrowth following the vegetative and boot-stage harvests. All entries flowered within 1 to 2 days of each other. Dry-matter yield increased for all grasses, but digestibility (IVDMD), crude protein, and elemental concentrations declined with maturity. Mean IVDMD values for all grasses were 741,642,534,485, and 444 mg g-1 for harvests 1 through 5 and 490 and 560 mg g-1 for the regrowth following harvest 1 and 2. The A. fragile entries had higher N, Ca, P, and Ca/P, but lower yield, IVDMD, and grass tetany potential values than other Agropyrons. Contrary to expectations, IVDMD of A. fragile decreased to 500 mg g-1 , 6 to 11 days earlier than for the other Agropyrons. The 1-28 and Hycrest entries had higher yield, IVDMD, K, and grass tetany risk and lower N, Ca, P, and Ca/P than the other Agropyrons