Effect of timing and intensity of first defoliation on subsequent production of 4 pasture species

Two simulated pasture studies were carried out at Swift Current, Sask., to determine the effects of date and height of first harvest in the year following establishment on the yield of 4 species in subsequent years. Altai wild ryegrass [Leymus angustus (Trin.) Pilger], Russian wild ryegrass [Psathyrostachys junceus (Fisch.) Nevski] and crested wheatgrass [Agropyron desertorum (Fisch.) Schult.] were used in both studies; alfalfa [Medicago sativa L. ssp. X varia (Martyn) Arcangelil] was included in the second study only. In both studies plots were first cut at 1 of 6 dates, approximately 2 weeks apart, during the period from mid-May to late July in the year following establishment. Cuts were made either at a 5 cm or at a 10 cm height to simulate medium grazing and light grazing, respectively. After the first cut, forage was harvested in that year whenever 10 cm of regrowth was present. In the next 5 years in the first study and 3 years in the second, all forage was harvested at 5 cm height on 15 May and thereafter whenever 10 cm of regrowth was present. Treatment effects were greatest in the year treatments were imposed and in the first post-treatment year. In the treatment year, highest forage yields were obtained from plots cut at 5 cm, but in subsequent years, forage yields were higher from plots cut at 10 cm in the treatment year. Moisture conditions in the seeding and establishment years affected the response to treatments. Date of first cut in the treatment year affected yields in subsequent years in both experiments although differences declined with time. Crested wheatgrass was more affected by date of first cut than were the other species. The cutting dates for highest yields in each case correlated with flowering date and indicate that seedings of these grasses should not be harvested until they have flowered. The results of this study also indicate that to ensure continued high forage yields, the first harvest of these grasses should be less intense than subsequent harvests.