Yellow Sweetclover (Melilotus officinalis)
Plant Characteristics: Biennial legume with coarse stems, serrated margins on leaflets. The petiole, or stem, of the middle leaflet of sweetclover is much longer than those of the other two leaflets. Flowers are yellow on a raceme.
Establishment: White sweet clover is well adapted to clay and loam soils, drought tolerant and winter-hardy. Plant sweetclover seed at the rate of 10-15 pounds per acre and at a depth of 1/4 - 1/2 inch. Spring seeding should be done from February 1 to April 15 because sweetclover requires a good supply of moisture and cool temperatures for germination and early seeding growth. These conditions are lacking when seeding is delayed until after small grain harvest. Late seeding tends to die the following year, with second year production reduced by about 25 percent. Sweetclover weevil could be a problem
Fertilization: Sweetclover tolerates a wide range of climatic and soil conditions and grow well on highly alkaline soils. Sweetclover requires at least moderately drained soil conditions and a pH greater than 6.5. If soil pH is below 6.0, apply lime well in advance of seeding. If more than 4 tons of lime are needed, at least half the recommended rate should be plowed down 6-12 months ahead of planting, with the other half applied just prior to planting and disked into the soil.
Adequate levels of phosphorus, potassium, and sulfur should be available for good growth and high production. Sweetclover should be fertilized similar to alfalfa. Follow soil test recommendations to determine fertilizer rates needed. As a rule, each ton of forage produced removes 10-15 pounds of P2O5 and 40-60 pounds of K20; so the same amounts must be returned to the soil in the form of fertilizer. Properly inoculated and nodulated sweetclover will not require the addition of nitrogen.
Grazing/Hay Management: Most forage production occurs from May to August with yields ranging from 1.5 to 2.5 tons/ac. Sweetclover do not tolerate close grazing or mowing during the first year of growth because regrowth occurs from stem buds rather than crown buds. A large amount of shoot and root growth can be produced during the second year. Growth occurs early in the season and declines rapidly after midsummer. Grazing may begin when plants are 12 to 14 inches, but must be rested during September and early October when buds are forming. Closer grazing within the seeding year markedly decreases second year production. In the spring of its second year, sweetclover is a prolific producer, and animal performance may equal that on alfalfa. Because second year spring growth is so rapid, start grazing when plants are 6-8 inches tall. If cattle keep this spring growth grazed down, the grazing season can be extended into July and August. A grazing pressure of 3-4 head per acre may be needed to prevent the crop from flowering and becoming woody.
Sweetclover is not a good hay species because it tends to be stemmy. If 19 to 24 inches of growth accumulate the first year, biennial sweetclover could be cut for hay. However, this may kill many of the buds and reduces second year production. To minimize that problem, cut after the root storage period of growth (early October) and leave at least a 6-inch stubble for winter protection. It might be possible to get more than one cutting from second year sweetclover, provided the first cutting is made in the bud stage. Sweetclover could be used for hay and should be cut before it blooms. Since the silage may contain dicoumarol, which causes sweetclover disease, wilt it to 65 percent moisture at ensiling, add 200 pounds of corn or 100 pounds of molasses per ton, and pack firmly.
Forage Quality: Quality is high if the crop is cut in the bud stage. Delaying cutting until full bloom results in stemmy, low-quality hay since the large, moist stems take longer to dry than the leaves, which become brittle and shatter badly. The percentage of crude protein and crude fiber in young plants are 21 and 19% and at hay stages these values are to 19% and 36% , respectively.
Bloat can be a problem. One risk with sweetclover is that coumarin is present in large quantities in the unimproved varieties. Coumarin may be converted to dicoumarol, a toxic product, during heating and spoilage. Dicoumarol reduces blood-clotting capability and may result in animals bleeding to death from slight wounds. Low-coumarin cultivars are available and should be used for forage applications
Varieties/Cultivars: Common, Madrid, Goldtop, Erector, and Yukon.