Seasonal trends in herbage yield and quality of Agropyrons.

Abstract

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, I-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 I-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.