McLeod (1982) gave as common names for the white species, white sweet clover and Bokhara sweet clover, and for the yellow species yellow sweet clover, official melilot, and common sweet clover.

Metcalfe (1985) listed several common names under the general heading of sweetclover, including annual yellow sweetclover (Melilotus indica All.), Banat sweetclover (Melilotus dentata [W. & K.] Pers.), yellow sweetclover (Melilotus officinalis Lamarck or Melilotus officinalis [L.] Lamarck), white sweetclover (Melilotus alba Medik. or Melilotus alba Desrousseaux), Daghestan sweetclover (Melilotus suaveolens Ledeb.), Israel (Hubam) sweetclover (Melilotus alba var. annua Coe), and sourclover or sour sweetclover (Melilotus indica All.).

The approved common and scientific names for the two species treated here are white sweet clover (Melilotus alba Desrousseaux) and yellow sweetclover (Melilotus officinalis [L.] Lamarck) (Metcalfe, 1985).

According to Duke (1981), yellow sweetclover comprises 3 subspecies and about 16 ecotypes and forms. Recommended cultivars include 'Albotrea.' 'Common Yellow,' 'Erector,' 'Madrid,' 'Switzer,' and 'Goldtop.'

Seeds of yellow sweetclover occur one or two to the pod and are smooth, ovoid-elliptical, 1.5-3 mm. long, ca 1.5 mm broad, and yellow or greenish-yellow, sometimes with purple spots. Seeds are said to poison horses (Duke, 1981).

Duke (1981) described yellow sweetclover as a biennial or annual herb with strong taproot; stems erect or ascending, 0.3-2.8 m tall, often tinged with red; leaves trifoliate, the leaflets of the lower and middle leaves broadly oval, lanceolate to rhomboid-ovate, 1-5 cm long, rounded at tip, those of upper leaves oblong-lanceolate, rounded or truncate at tip, irregularly dentate or entire; stipules entire, 8-12 mm long, lanceolate or subulate; racemes lax, 30-80 flowered, 4-15 cm long; pedicels 2-2.5 mm long; clayx 2-3 mm long, teeth as long as tube or shorter; corolla yellow, 4.5-7 mm long, standard and wings more or less equal to or up to 1 mm longer than keel; style 1.7-2.3 mm long, often persisting; ovules 4-6, rarely 3 or 8; pods ca, 3.4 mm long, 2-2.5 mm broad , 1.5 mm thick, compressed with strong rugose transverse veins or wrinkled gray to straw-colored, rarely black, obtuse at tip.

Duke, (1981) detailed the thermal tolerances for the sweetclovers. White sweetclover tolerates an annual mean temperature range of 5.7-24.3 C, with the mean of 54 cases being 12.7; the corresponding figures for yellow white sweetclover are 4.9-21.8 C, with the mean of 47 cases being 10.9 C . White and yellow sweetclovers tolerate high and low temperatures and are seldom winter-killed. Both species are said to be tolerant of both heat and frost. There are intervarietal differences in winterhardiness for white sweetclover, with 'Arctic' and 'Polara' both tolerant of Canadian conditions. For yellow sweetclover, cv 'Madrid' was noted as relatively resistant to fall freezes.

Based on Duke's (1981) account, yellow sweetclover is assigned to the Eurosiberian and Mediterranean Centers of Diversity, and is native from Europe to central temperate Asia and western China, south to North Africa, Ethiopia, Eritrea, and Kenya, and has been introduced to various temperate reions, including North and South America. It is cultivated in India. It ranges form the Boreal Moist through Warm Temperate Thorn to Moist Forest Life Zones, and persists up to an altitude of 4,000 m. In California, Munz (1973) noted that yellow sweetclover is less commonly naturalized than white sweetclover or sourclover. According to McLeod (1982), sweetclovers will grow almost anywhere, given sufficient and suitably-distributed rainfall. They grow in southern Canada and throughout the United States, thriving in both semiarid and humid regions.

Sweetclovers grow well where annual rainfall exceeds 17 inches, suitably distributed throughout the year, and often persist in areas too dry for alfalfa. Yellow sweetclover withstands drier conditions than white (McLeod, 1982).

Zachariassen and Power (1991) found that crimson clover showed a consistently-higher water use efficiency (g of dry matter produced per liter of water evapotranspired) than hairy vetch at 10, 20, and 30C. White sweetclover showed intermediate values.

Goldstein (1989) wrote that principal considerations in drought-proofing a farm on the northern Great Plains are: (1) improving soil structure through integrated use of grasses, (2) integrating animals with grain-farming operations, (3) effective management of yellow sweetclover, (4) stubble mulching to improve infiltration of water, and (5) timing tillage to have maximum positive impact on soil improvement. Yellow sweetclover is useful when grown in combination with a brome grass or a winter-hardy orchard grass like cv 'Pierre'. This is better than a solid stand of yellow sweetclover for both soil improvement and grazing. Such a mixture could be grazed or stubble mulched by undercutting the plants and leaving the residue on the surface. This approach to tillage leads to better water infiltration and efficiency of nitrogen use in the following grain crops than does plowing.

McLeod (1982) ascribed to sweetclovers the ability to convert the insoluble nutrients phosphorus and potassium from forms unavailable to other plants.

Sweetclovers are intolerant of acid soils (Duke, 1981; Brinton, 1989). According to Johnny's Selected Seeds (1983), white sweetclover requires soil pH of at least 6.8. and best growth occurs on neutral or alkaline soil with abundant lime. If soil pH is less than 6, soil should be limed well in advance of seeding (McLeod, 1982).

McLeod (1982) confirmed that sweetclovers tolerate cemented clays and gravels to poor sand and stated that the the deep roots open the subsoil. He also mentioned that the white species prefers clay loams and that the yellow does best on loam soils.

Madson (1951) stated that sweetclover tolerates loam to heavy soil types.

Schonbeck (1988) wrote that yellow sweetclover does well on soils that will not support true clovers (Trifolium spp.).

In New York state, Scott and Burt (1985) evaluated cover crops after overseeding into corn 6-18" high were medium red clover, mammoth red clover, alfalfa, yellow sweetclover, alsike clover, birdsfoot trefoil, Canada field peas, Austrian winter peas, cowpeas, perennial or annual ryegrass, medium red clover + ryegrass, or medium red clover + rye. Of these, alfalfa, medium red clover, yellow sweetclover, hairy vetch, ryegrass, and medium red clover + ryegrass have performed well.