The energy needed for regrowth of perennial forages in the spring comes from stored reserves of total nonstructural carbohydrates (TNC). These are the food reserves used by plants to develop cold tolerance, to live through the winter and to initiate growth after each cutting. TNC reserves derived from photo-synthetic activity are stored in various plant tissues which varies according to plant species.
When alfalfa commences growth in the spring, TNC energy stored in the roots and crown is used in the formation of new top growth from crown buds. Depletion of these energy reserves continues until the plant is able to photosynthesize more than sufficient energy in leaves to meet growth requirements and begins to replenish TNC storage in the roots. Storage continues and reaches its highest level in the roots, usually about the full bloom growth stage.
After the first crop is cut the process of TNC food reserve depletion and renewal is repeated for each successive new growth. Quality of first spring harvest of established alfalfa is highest at the early bud stage but seasonal yield of forage and total digestible nutrients (TDN) are maximized by delaying the first harvest until the one-tenth bloom stage.
Careful management of new seedings is especially important in the seeding year to ensure a long-lived productive stand. New seedings should not be harvested until plants have come to at least the one-half bloom stage to ensure adequate storage of TNC in the roots. This management should be followed for all harvests in the seeding year. Established stands of alfalfa can survive earlier harvesting in the spring than that recommended for new seedings.
Removal of first cuttings at the full bud stage in the spring does not reduce the annual forage yields appreciably. It may even be necessary to spread the harvest period of each cut or may be desirable to improve forage quality and to prevent overmature hay crops. Because the effects of early cutting are accumulative, the practice of cutting at early growth stages should be rotated among alfalfa fields. Alfalfa stand will not be reduced from a single cut at the bud stage, provided successive cuttings are permitted to reach at least the one-tenth bloom stage of maturity.
Stage of bloom serves as a useful index for determining when to harvest alfalfa. Prolonged cool moist cloudy weather can delay the appearance of blossoms in alfalfa. Thus when these conditions occur the activity of new shoots at the crown should be checked. If these shoots, which will form the next crop, begin to elongate, the first harvest should be removed even though blossoms are not visible. If delayed, these new shoots will continue to elongate and will be removed with the forage harvest. The next harvest would then be reduced and delayed.
Late summer-fall harvest management of alfalfa is critical to winter survival and spring regrowth. Crown bud number begins to be determined in late summer and continues to increase until the alfalfa plants go dormant. These crown buds grow in length and size until the winter dormant stage, and are important since the following spring the growth of the crown buds produce the stems and leaves which make the yield of the first hay crop.
Since the first crop yields are related to the number of crown buds formed the previous fall, the management should be to promote the crown bud development. The buildup of TNC reserves in crowns and roots is also important for winter survival and spring regrowth. Thus fall management should allow a minimum period of 6 weeks for regrowth before taking a fourth cut or before the arrival of the first killing frost.
In taking a fall harvest of alfalfa, sufficient stubble (4 to 6 inches) should be left to collect snow and aid survival under ice conditions. Under many circumstances taking a fourth cut will not out-weigh the winter survival risk or provide sufficient yield to justify the harvesting cost.
Spring growth of birdsfoot trefoil originates from overwintering crown buds similar to that found in alfalfa. Stems for successive harvests also originate mainly from auxiliary buds at the crown.
However, in birdsfoot trefoil some regrowth may occur from buds formed in the axils of the leaves on the old stems. Under a hay management system when the first harvest was removed at ½ to full bloom, Pennsylvania data showed highest forage yields were obtained for the season with a 6-7 week harvest schedule. With hay management, cutting heights of about 2 inches seem to be most satisfactory for birdsfoot trefoil. Cutting at this height will save some green leaves and auxiliary buds so that more rapid regrowth takes place.
Red clover and alsike clover form tiller-like branches at the crown in late summer and early fall. The following season's growth arises from these overwintering tiller branches. Under favorable climatic and soil conditions these tiller branches frequently develop into floral stems during the seeding year, and which may set seed during the fall period. This depletes the root reserves and such plants seldom survive into the next season. Management of these legumes during the late summer and fall period of the seeding year should be to prevent floral stem and seed formation. This can best be accomplished by clipping or grazing. In established stands hay crops should be removed at the early bloom maturity stage.
White clovers including ladino spread by stolons and are best suited for grazing. Because they have shallow root systems they do not tolerate drought. White clovers will not persist under dense shade of companion grasses so grazing management should be to prevent the grass getting so tall that it smothers out the legume.
Stephen J. Herbert
Dept. of Plant and Soil Sciences
University of Massachusetts Amherst
Crops, Dairy, Livestock News. Vol. 1:2, Summer 1996
Last updated: 3/15/05.