Responses of Biennial Sweetclovers of Diverse Latitudinal Adaptation to Various Management Procedures in Alaska

Leslie J. Klebesadel, Emeritus Professor of Agronomy

Agricultural and Forestry Experiment Station; Palmer, Alaska

Bulletin 98; June 1994 (19 pages)

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Summary

This report summarizes eight experiments with sweetclover (Melilotus species). Objectives were (a) determine responses of numerous cultivars and strains, representing a wide range of latitudinal adaptation, to various management procedures, (b) identify management options that contribute to improved winter survival, (c) delineate management procedures for maximizing yields, nutritional value, and usefulness of sweetclover for forage production in Alaska, and (d) identify logical avenues for future management research with sweetclover in this north-latitude area.

Species of sweetclover included were biennial yellow (M. officinalis), biennial white (M. alba), and annual white (M. alba var. annua).

All experiments except one were conducted at the University of Alaska's Matanuska Research Farm (61.6oN) near Palmer in southcentral Alaska; one experiment was conducted at the Fairbanks Experiment Farm (64.9oN) in central Alaska's Tanana Valley.

Experiment I - Time of Planting, Rows:

Four strains of biennial white sweetclover of diverse latitudinal adaptation, were planted in rows without a companion crop at 10-day intervals (from May to August) and thinned to individual plants during two consecutive years. Objectives were to determine influence of planting date on seeding-year phenological development, winter survival, and subsequent forage yield.

Strains used and latitudinal adaptation of each were: (a) The cultivar Spanish adapted at 35o to 48oN in the conterminous U.S., (b) the cultivar Arctic grown at 50o to 56oN in Canada, (c) an Alaskan selection (AK-Syn.1) derived principally from Arctic at 61.6oN, and (d) Matanuska white, a selection from a roadside population that has undergone many generations of adaptive modification at 61.6oN in southcentral Alaska.

· All strains flowered in the seeding year when planted prior to mid-June.

· Spanish winterkilled completely in both tests, regardless of planting dates. Winter survival of Arctic,

and to a lesser extent AK-Syn.1, was usually best with planting in early July. Earlier planting resulted in tall growth resembling annual habit during the seeding year, followed by generally poorer winter survival. Winter survival of Matanuska white was best with earliest planting dates. All strains winterkilled completely when planted later than late July.

· Second-year forage yields were highest from AK-Syn.1, intermediate from Matanuska white, and lowest from Arctic. Yields changed little for each of the strains for planting dates from 10 May to 10 June, but declined rapidly for later planting dates. Second-year forage yields were lowest from rows planted on 21 July and none were obtained from rows planted on later dates due to total winterkill.

· Herbage yield per surviving plant the year after planting was highest with earliest planting and gradually lower with progressively later planting dates.

· Natural selection in Alaska toward improved adaptation has resulted in (a) a sweetclover population (Matanuska white) with winter survival unaffected by flowering during the seeding year, and (b) a selection (AK-Syn.1) derived primarily from Arctic that was consistently superior to Arctic in winter survival.

Experiment II - Influence of Seeding-Year Harvest vs. Non-Harvest on Subsequent Winter Survival of 10 Strains of Biennial Sweetclover:

· The southernmost-adapted cultivars Denta, Spanish, and Goldtop winterkilled 100%, whether harvested or not in late September.

· Cultivars Cumino, Erector, and Madrid winterkilled 100% where harvested, and survived at very low rates (<8%) where not harvested.

· Winter survival was better with more northern-adapted strains but seeding-year harvest invariably and in some cases markedly decreased winter survival of those strains. Percents winter survival in rows harvested vs. not harvested, respectively, were: Arctic 55% and 73%, AK-Syn.1 75% and 86%, Matanuska white 83% and 89%, and Arctic Circle strain 40% and 78%.

Experiment III - Effects of Time of Seeding-Year Harvest on Seeding-Year Forage Yields, Winter Survival, and Second-Year Forage Yields:

· Seeding-year forage yields of AK-Syn.1 biennial white sweetclover broadcast-seeded 8 June increased continuously with progressively later harvests at 10-day intervals from 0.04 T/A on 20 July to 2.52 T/A at final harvest on 20 September.

· Percent crude protein in seeding-year forage declined from 33.7% at 20 July harvest to 13.6% at 20 September harvest.

· Stored food reserves in roots (3 treatments sampled) were considerably higher where plants had no topgrowth removal until 6 October than where plants were harvested 10 August or 10 September; plants were slightly lower in stored food reserves following 10 September than 10 August harvest.

· Winter survival was modest following all seeding-year harvest dates, averaging 29%; best survival was 40% following earliest (20 July) harvest and poorest (11%) following harvest on 30 August.

· Plants were shortest and forage yields lowest in the second year where seeding-year harvest had been on 30 August. In general, plant heights and forage yields were increasingly higher where seeding-year topgrowth removal had been progressively earlier or later than 30 August, with tallest plants and highest yields occurring where seeding-year forage harvest had been earliest (20 July) or latest (6 October).

Experiment IV - Influences of Two Planting Dates on Seeding-Year Forage Yields, and on Proportions and Crude Protein Concentrations of Leaves and Stems in Herbage of 12 Strains:

· The annual Hubam and the southernmost-adapted biennial cultivars (which grew tallest) produced highest seeding-year forage yields.

· Forage of the tallest-growing cultivars, especially the annual Hubam, was comprised of lower percentages of leaves and higher percentages of stems than the shorter-growing strains.

· Plants of all strains in the earlier-planted (25 May) rows were both taller and contained lower percentages of leaves at the 21 September harvest than plants in later-planted (12 June) rows.

· Over all strains and both planting dates, mean percent crude protein was 24.0% in leaves and 6.8% in stems at harvest on 21 September.

· Percent crude protein at harvest on 21 September was slightly higher in both leaves and stems (25.9% and 7.7%, respectively) of later-planted (12 June) rows than in rows planted 25 May (22.2% for leaves and 5.9% for stems).

· With all strains, forage yields harvested 21 September generally were much higher from rows planted 25 May than those planted 12 June; although later planting reduced the growing period by only 15%, mean

forage yields were reduced 30%.

Experiment V - Annual Forage Production of Madrid Sweetclover as Influenced by Three Planting Dates and Various Row Spacings vs. Broadcast Seeding:

· Seeding-year forage yields on 21 September were highest with earliest (10 May) planting, intermediate with intermediate planting date (29 May), and lowest with latest planting (16 June).

· Planting in rows 18 inches apart resulted in generally higher forage yields, with all three planting dates, than broadcast seeding or rows planted 12, 24, or 30 inches apart.

Experiments VI, VII, and VIII - Seeding-Year Forage Production of 11 Diversely Adapted Strains Seeded on Different Dates in Three Different Years:

· Seeding-year forage yields of all 11 strains were highest in the year that planting was earliest (20 May), and lowest in the year that planting was latest (9 June).

· The annual Hubam, and cultivars of both white and yellow biennial sweetclover that were farthest from their latitude-of-adaptation (when grown in Alaska), grew tallest and produced highest forage yields.

General Summary and Recommendations

· Lowered winter survival resulting from utilization of biennial sweetclover (spring-seeded without a companion crop) for forage in the seeding year suggests that attempts generally will not be successful that seek to utilize the crop for maximum forage production in both years of its growth. Therefore, it appears that sweetclover culture in this high-latitude area can be conducted in either of two distinct ways, each with a very different type of sweetclover strain. Those two avenues are:

· (a) Annual forage production: Plant nonhardy, tall-growing, leafy, southern-adapted, low-coumarin cultivars as early as possible in rows about 18 inches apart with effective weed control. Expect no winter survival.

· (b) Utilization as a biennial for second-year forage production: Seed early and use the most winterhardy biennial sweetclover strains planted in association with a cereal companion crop. The companion crop should be removed at an immature stage for forage leaving a tall stubble. Early seeding and early companion-crop harvest can guard against damaging effects of companion-crop lodging and provide a longer late-summer period for sweetclover seedling growth free of the cereal crop competition. Leaving a tall stubble insures against injurious, too-short clipping of sweetclover seedlings; moreover, tall stubble holds protective, insulating snow cover in place against the removal force of strong winter winds.