Bromegrass in Alaska. VI. Effects of a Broad Array of Harvest Schedules and Frequencies on Forage Yield and Quality and on Subsequent Winter Survival of Cultivars Manchar and Polar

Leslie J. Klebesadel, Emeritus Professor of Agronomy

Agricultural and Forestry Experiment Station; Palmer, Alaska

Bulletin 104; September 1997 (32 pages)

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SUMMARY

Objectives of this study were to compare several schedules and frequencies of forage harvest of smooth bromegrass (Bromus inermis Leyss.): (a) for distribution of forage yields and total productivity in the year of differential harvests, (b) for percent crude protein in herbage in the various cuttings and for yields of crude protein, (c) for determining rates of growth (production of herbage dry matter) during the growing season, and (d) for effects of those different harvest schedules and frequencies on subsequent winter survival and on stand health and vigor the following year as measured by a uniform evaluation harvest in late June or early July.

Two bromegrass cultivars, mid­temperate­adapted Manchar and subarctic­adapted Polar, were utilized in four experiments (Manchar in two, Polar in two) conducted at the University of Alaska's Matanuska Research Farm (61.6°N) near Palmer in the Matanuska Valley in southcentral Alaska.

·All of the more frequent harvests (3, 4, or 5 per year) resulted in lower total forage yields than the highest­yielding two­harvest treatments (All Exps.).

·During the entire month of June and into early July, smooth bromegrass supplied with adequate fertilizer nutrients and soil moisture put forth remarkably rapid growth, producing high forage yields (Exps. III, IV).

·Rate of forage dry­matter accumulation during most of the month of June ranged from 70 to 197 pounds per acre per day, and much of the difference among rates appeared related to differences in moisture supply (Exps. II, III, IV).

·The highest rate of herbage dry­matter production during a measurable short period in these experiments was 273 pounds per acre per day from 3 to 10 June with Polar bromegrass when it benefited from abundant soil moisture following markedly above­normal precipitation during May (2.54 inches received versus normal = 0.74 inches) (Exp. IIIb).

·With two cuttings per year, the first about 20 June and second about 1 September, approximately one half of the total­year yield was obtained in each cutting; with the first cutting about 1 July (and the second about 1 Sep.), averages of 57% and 43% were obtained in first and second cuttings, respectively. However, relative abundance or scarcity of precipitation in either half of the growing season had a strong influence on yield distribution (Exps. II, III, IV).

·In general, little or no increase in herbage yields accrued from deferring the second of two cuttings to later than late August or very early September. With three cuttings, some increases were obtained with progressively later third cuttings throughout September; however, those late cuttings interrupted the final, pre­winter regrowth period and sometimes predisposed stands to severe winter injury (Exps. II, III, IV).

·Percent crude protein in first­cutting herbage declined from 19.3% on 2 June to 13.1% on 2 July, the latest of four first­cutting dates (Exp. II).

·With two harvests per year, percent crude protein in the second cuttings was highest when the first cutting was taken latest (2 July), lowest when the first cutting was taken earliest (10 June), and intermediate with the intermediate first­cutting date of 22 June (Exp. II).

·Similarly, within each of three groups of treatments (first cuttings harvested on three different dates), as second cuttings were progressively later by about 10­day increments (from 20 July to 22 Sep.) percent crude protein in harvested herbage declined with each later harvest. Thus, as with first cuttings, percent crude protein in the regrowths declined as that grass became more mature with longer periods of growth before harvest (Exp. II).

·With frequent harvests (4 or 5 per year), percent crude protein in herbage remained high in all regrowth harvests, ranging mostly from 25% to 34% (Exp. II).

(mean = about 15 inches annually) is marginal for realizing the full forage­production potential of bromegrass. Above­normal amounts promote high forage yields, but below­normal precipitation can severely limit productivity. Moreover, the timing of precipitation during the growing season can markedly influence forage productivity of bromegrass.

·Because rainfall during April, May, and June at the Matanuska Research Farm typically is very limited (normal = 0.63, 0.74, and 1.59 inches, respectively), any deficiencies in those precipitation amounts severely curtailed the very considerable potential for rapid herbage production by bromegrass during June and early July; moreover, that suppressing effect on productivity was magnified if precipitation was much below normal during the latter portion of the previous growing season (Exps. II, III, IV).

·With two cuttings per year, moisture supply had a marked effect on amount of regrowth produced after the first cutting; for example, in Exp. II with first cutting on 22 June, and with June+July+August precipitation 1.41 inches above normal, second­cutting yield on 22 September was 2.80 T/A; in Exps. III and IV, with the same first­cut date and when precipitation for the same months averaged 1.44 inches below normal, yield on 21 September (mean date) averaged only 1.63 T/A.

·Northern­adapted bromegrass harvested on an appropriate frequency and schedule, one that is in harmony with grass growth requirements and seasonal physiological processes (first cut late June or very early July, second cut late August or very early September), sustained little or no reductions in stand vigor or winter survival. Conversely, inappropriate harvest frequencies or scheduling (usually 3 to 5 cuts per year) tended to weaken stands and predispose them to moderate­to­severe winter injury (Exps. I, II, IV).

·A winterhardy, northern­adapted bromegrass cultivar, well supplied with soil moisture and recommended rates of fertilizer nutrients and harvested only twice, will produce high yields of good quality forage and will not be weakened in stand vigor as generally occurs with more frequent harvests (All Exps.).

·Although these experiments simulated farm­equipment harvest of forage as done for storage or green­chop feeding, the more frequent harvests, their scheduling, productivity, regrowth rates, and herbage quality can relate broadly to bromegrass utilization by rotational grazing also.

·Total yields of crude protein ranged from 443 to 1398 lbs/A; however, the lowest yields were from 2­cut treatments with early second cuttings that did not recover crude protein in unharvested regrowth that developed after those early second cuttings (Exp. II).

·Highest yields of crude protein (1398 and 1337 lb/A) were obtained from 5­cut and 4­cut treatments, respectively. However, those treatments were lower in total dry­matter yields than many of the 2­cut treatments, and most of those 4­ and 5­cut treatments predisposed the bromegrass to severe winter injury (Exp. II).

·Among all 2­cut treatments, highest total yields of crude protein (1026 to 1114 lb/A) generally were obtained from treatments with the second cutting harvested at the end of August; earlier or later second cuttings tended to result in lower total­year yields of crude protein (Exp. II).

·The combination of a stressful winter following 34 different harvest treatments with Manchar bromegrass revealed in considerable detail the markedly different effects of the various harvest schedules, frequencies, and lengths of regrowth periods on subsequent winter survival and stand vigor as measured by first­cut yields the following year (Exp. II).

·Most of the 13 treatments involving three, four, or five harvests per year were more damaging to Manchar winter survival and stand vigor than any of the 21 treatments with two harvests per year (Exp. II).

·With three or four cuttings, Manchar stands were predisposed to maximum subsequent winter injury (almost total winterkill) when the final harvest was taken on 10 September; slightly less, but still very severe, injury occurred where the final cutting had been taken on 31 August or 22 September. Greatest injury with five cuttings occurred where the final harvest had been on 22 September (Exp. II).

·Polar was most injured by two 3­cut treatments with first cutting on 12 June, the second on 20 July, and the third on either 1 or 12 September. Strangely, those treatments were more injurious to Polar stands than 4­cut or 5­cut treatments, all of which had shorter regrowth periods between cuttings, and regardless of final cutting dates from 21 August to 22 September (Exp. IV).

·Dates of occurrence of first killing frost in autumn (about 24°F) can differ greatly from year to yearduring the years of these experiments the range was 16 September to 18 October.

·The amount of precipitation received in this area