Growing conditions during September and early October are frequently favorable for alfalfa growth. Producers observing this growth may desire to harvest during this period. Increased emphasis on alfalfa production, higher hay values and recently developed alfalfa varieties have renewed questions on the possibility of making a harvest after onset of dormancy in late October or during November.
Alfalfa stores energy in the roots and crowns. These energy reserves are used by the plant to survive over winter, to develop cold tolerance, and to initiate spring growth and growth after each cutting.
When alfalfa initiates growth in the spring, plant reserves stored in the roots and crowns are used to start this new growth from crown buds. Depletion of stored reserves continues until the plants are at least six to eight inches tall. By this time energy products are being synthesized in the leaves more rapidly than is being used for growth and some storage begins. This storage continues and reaches its highest level at about full bloom.
Following the cutting of the first crop, preferably at mid to late bud stage, this process of food reserve depletion and renewal is repeated and continues for each subsequent cutting. Root reserves are not at their highest level at the bud stage of growth. However, plants can usually maintain a satisfactory level of reserves for the growing season.
In terms of persistence, spring, summer and fall cutting management are related. Research has determined that when harvests are made at late bud-early bloom stage of development, the fall cutting schedule is important for stand maintenance. Make the last regular harvest by the calendar: northern Ohio, September 1 to 7; central Ohio, September 3 to 12; southern Ohio September 5-15. This means that on those fields with an intensive cutting schedule, no harvest should be taken from early-mid September to mid-October. At least 30 days between the last regular harvest and killing frost are needed to adequately restore root and crown reserves. Research from Iowa indicates alfalfa yields were 0.61 tons per acre lower the following harvest year where a harvest was made during this period the previous fall. This trial included both the older adapted varieties and more recently developed varieties, with the carryover effect similar among all varieties.
Both Pennsylvania and Michigan have reported when the first cutting is delayed until mid-bloom, early to mid-June in Ohio, or when cutting intervals are lengthened to 42-45 days, the detrimental effect of harvesting on any date in the fall is lessened. However, it's still not wise to cut alfalfa stands on a regular basis from mid-September to mid-October and especially not the same field year after year.
Alfalfa growth which accumulates by October 15-20 may be harvested when adequate growth is present to merit the harvest procedure. Observations indicate this quantity varies greatly from year to year. Ohio research has shown the quality of this accumulated material to be high, usually 20 percent or more crude protein. However, the quantity of this harvest varies each year, from approximately one ton per acre some years to minuscule quantities in other years.
Because of cooler temperatures, shorter days, higher humidity and moisture, it is usually not possible to harvest this late growth as dry hay. The common method of harvest would be for silage. Seldom will there be sufficient regrowth to significantly lower root plant food reserves.
Raising of the alfalfa roots from the soil is called heaving. This is caused by fluctuating temperatures above and below freezing, thus raising the alfalfa root from the soil and destroying the plant. Several conditions are necessary for frost heaving to occur. These c
onditions include a highly frost susceptible soil such as a silt loam or clay soil, high soil moisture content, and temperatures just below the soil surface registering 32 degrees F or lower. A lack of mulch or snow cover contributes to this frost formation within the soil.
The winter of 1985-86 resulted in severe heaving in many areas of northern Ohio. A harvest management trial at the Ohio Agricultural Research and Development Center at Wooster was severely damaged by heaving. A study of this area indicated management of the alfalfa can influence the heaving problem.
Plots with alfalfa harvested in the late fall on October 20 showed severe damage with 38 percent of plants heaved, compared to only 5 percent of the plants heaved where no crop was harvested on October 20. The most heaving, 53 percent, occurred where the alfalfa was harvested on a vigorous 30 day schedule with five harvests from May 15 through September 15. The primary relationship with percent of heaving appeared to be lack of soil cover resulting from the late harvest or from poor fall regrowth following frequent harvests during the summer.
Alfalfa producers thinking of making a late harvest should consider their need for the extra forage contrasted to the possible risk of losing a portion of the alfalfa stand during the winter from heaving.
Suggestions to minimize the problems of late harvest include:
Prepared and Distributed by:
Donald K. Myers
Extension Agronomist Emeritus
R. W. Van Keuren
Professor Emeritus, Agronomy
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