Bromegrass in Alaska. IV. Effects of Various Schedules and Frequencies of Harvest on Forage Yields and Quality and on Subsequent Winter Survival of Several Strains
Leslie J. Klebesadel, Emeritus Professor of Agronomy
Agricultural and Forestry Experiment Station; Palmer, Alaska
Bulletin 102; October 1994 (22 pages)
SUMMARY
Effects of different annual harvest schedules and frequencies on several cultivars and strains of bromegrass (Bromus species) were measured in five field experiments at the University of Alaska's Matanuska Research Farm (61.6oN) near Palmer in southcentral Alaska. Most cultivars evaluated and compared were smooth bromegrass (B. inermis Leyss.). Native Alaskan pumpelly bromegrass (B. pumpellianus Scribn.) and the predominantly hybrid (B. inermis x B. pumpellianus) cultivar Polar, developed in Alaska, were included also.
· Bromegrasses compared showed a considerable range of inherent winterhardiness. Saratoga sustained less winter injury and yielded more than Sac; however, both of those southern-type cultivars were inferior in winter survival to all of the more northern-adapted strains compared.
· Although all cultivars were not compared in every experiment, results generally ranked winterhardiness of strains as follows: Native pumpelly > Polar > Carlton = Canadian commercial > Manchar > Saratoga > Sac > Achenbach.
· The different harvest schedules and frequencies resulted in dissimilar total annual forage dry-matter yields as well as differences in herbage quality in individual harvests as measured by crude protein concentration in the herbage.
· Three, four, or five harvests per year generally resulted in lower total annual dry-matter yields than two harvests per year.
· Crude protein concentration was highest, and percent dry matter lowest, in herbage cut frequently (3, 4, or 5 times per year) and therefore at the more immature stages of plant development.
· Interruption of the very rapid growth of bromegrass during June, with harvest prior to late June, resulted in marketdly lower first-cut yield, a slow rate of grass regrowth, and decreased total annual forage yield.
· First-cutting dry-matter yields in mid-June were approximately half of first-cutting yields obtained only two weeks later.
· With two harvests per year, no increase in total annual forage yield accrued from deferring the second harvest to the late-September/early-October period; moreover, quality of second-cutting forage was higher with harvest in late August or very early September than in late September or early October.
· Little consistent difference was noted in total forage yield during the year of differential harvests among the introduced northern-type smooth bromegrass strains (cultivars Carlton and Manchar, and Canadian "commercial"), or the Alaska cultivar Polar.
· The various harvest schedules and frequencies influ
enced subsequent winter survival when winters were moderately to severely stressful. Three harvests per year frequently predisposed Carlton, Canadian commercial, Manchar, and occasionally Polar, to markedly greater winter injury (and lower first-cutting forage yields the following year) than two harvests.
· When three harvests per year resulted in significant subsequent winter injury of brome strains, taking the third harvest in mid-September resulted in more injury than a third harvest in early October.
· When winter injury occurred following two harvests per year, it was more severe when the second harvest was taken in late September or early October than with the second harvest approximately one month earlier in late August or very early September.
· Native pumpelly bromegrass often yielded less than the northern-type smooth bromes; however, when winter injury of those strains was moderate to severe, pumpelly brome surpassed all other strains in sustaining least winter injury and consequently produced higher first-cutting forage yield the following year.
· Total annual yields of crude protein ranged from 780 to 1209 lb/A with little relationship between protein yield and harvest treatments.
· Adequacy of early-season rainfall, especially during April and May (which normally are modest-rainfall months in this area), was very important toward realizing the full forage-production potential of the usually very heavy spring growth of bromegrass.
· The duration of the final regrowth period prior to winter appeared to be important to continued bromegrass stand vigor. Interruption of that last regrowth period with a final harvest in mid-September or later was more damaging with three than with two cuts per year.
· With intensive utilization (frequent harvests) of bromegrass during the first half of the growing season, uninterrupted regrowth after about mid-August apparently permitted stands to restore good energy status prior to winter.
· Three major factors influence winter survival of bromegrass in this area: (a) the severity of winter stresses during each winter, (b) the inherent winterhardiness of the bromegrass cultivar or strain used, and (c) harvest schedule and frequency. Factor (a) is unpredictable and uncontrollable; however, (b) and (c) are controllable, and prudent choices can ensure against stand loss from winter injury or total winterkill. Polar is the most winterhardy cultivar currently available, and harvest schedule and frequency should be in harmony with the grasses' seasonal growth pattern and physiological processes. Two harvests per year, the first near late June/very early July and the second in late August/very early September should provide high yields of good quality forage and insure against weakening the grass stand.