Clovers (Taylor, 1985).

Trifolium (Taylor, 1985).

The genus Trifolium contains about 240 species (Gillett, 1985).

According to the review by Gillett (1985), Musil (1963) wrote a descriptive key to seeds of 32 clover spp., including 9 of agricultural importance. Gillett (1985) wrote that color of seed can vary with maturity, and size and shape of seed can vary, with variability in the latter based on crowding. The hilum has not been a useful structure upon which to base taxonomic distinctions. Seed size, shape, and color are the most useful characters.

The attitude of the radical and its length relative to the cotyledons are useful taxonomic characters in distinguishing among Trifolium spp. (Gillett, 1985).

All Trifolium possess the typical papilionaceous legume flower with ten stamens; leaves usually comprise three leaflets, but a few species have five leaflets per leaf (Taylor, 1985).

For most Trifolium spp., growth is limited to the cool part of the year; species that perform as perennials in the northern United States may behave as winter annuals in the Southeast (Taylor, 1985).

Trifolium spp. inhabit the temperate regions of the world; some are native to North America, but most of agricultural interest were introduced from Europe. From sixty to 65 species of Trifolium are from the American center of diversity, 150-160 from the Eurasian, and 25-30 from the African (south of the Sahara) (Taylor, 1985).

According to Taylor (1985), Trifolium spp. inhabit temperate regions of the world and require a cool, moist climate, or their growth is confined to seasons where such weather conditions prevail.

Based on the account by Murphy et al. (1976), fertilization at planting time should depend on the previous history of the field and the available soil phosphorus. The latter can be determined in a commercial soil-testing laboratory by the sodium bicarbonate-extraction soil test. If the field has not been previously fertilized or the phosphorus is less than 5 ppm, apply about 500 pounds single superphosphate per acre, to supply both phosphorus and readily available sulfur. Where soil tests show more than 5 ppm phosphorus, less fertilizer may be used. Additional nitrogen increases competition from grass species in newly-seeded pastures and reduces nitrogen fixation.

Many grasslands show phosphorus deficiencies. Clover plants growing without sufficient phosphorus are small, with small, dark-green leaves. Soil phosphorus levels are rated as very low (5 ppm); low (5 to 10 ppm); intermediate (10 to 20 ppm); and high (over 20 ppm). Based on those ratings, fertilizer should be applied as follows:

After two or three heavy applications on low-phosphorus soils, only maintenance amounts should be required. If soil phosphorus is high, light applications every second year increase clover production by replacing phosphorus and sulfur removed by grazing (Murphy et al., 1976).

Single superphosphate also supplies sufficient sulfur (about 12%) except where rainfall is greater than 30 inches. In wet areas, apply about 50 lbs/acre of sulfur in alternate years. If a high percentage of the sulfur will not pass through a 50-mesh screen, use from 100 to 200 lbs/acre. The larger particles will last longer. After the first year, the clover can be more heavily grazed if the soil phosphorus and sulfur supplies are adequate (Murphy et. al, 1976).

Clover rhizobia require a soil pH of greater than 5.0 but usually less than 10.5 (Burton, 1985). Clover growth is best in the soil pH range of 6.0-7.0 (Blue and Carlisle, 1985).

Trifolium spp. will grow on a wide range of soil types (Taylor, 1985).

Kendall and Stringer (1985) reported that competition for sunlight is a major aspect in both intraspecific and interspecific dynamics, leading to domination of stands by clovers that express rapid regrowth or tall stature.

Burton's (1985) review indicated that whereas some strains of Rhizobium trifolii tolerated salinity, others did not. Kendall and Stringer (1985) wrote that most Trifolium spp. do not grow in highly saline soils, and often are more adversely affected than are grasses. Berseem, rose, and some varieties of subterranean and strawberry clovers are moderately tolerant of salintiy. Alsike, red, white dutch, and ladino clovers are said to show low tolerance.

The following account is based on that of Lee (1985). Herbicides applied before clover is seeded include EPTC, benefin, and propham. Prophamare can be applied after seeding but before emergence. After emergence of clover seedlings, propham, chlorpropham, and pronamide can be applied. Broadleaf weeds can be reduced in seedling stands of red or ladino clovers, dinoseb or 2,4-DB are appropriate herbicides. In mixed stands of clovers and grasses, postemergence application to control broadleaf weeds are the only options. MCPA and amine formulations of 2,4-D are useful in mixtures of alsike, ladino, or red clovers and cereals.

For most Trifolium spp., growth is limited to the cool part of the year; species that behave as perennials in the northern United States may behave as winter annuals in the Southeast (Taylor, 1985). Cold, foggy midwinter conditions do not favor growth of clovers, and they often appear unthrifty during such periods (Murphy et al., 1976).

Seeding rates vary greatly among the Trifolium spp. (Van Keuren and Hoveland, 1985).

Clover seed should be placed no more that 1/2 in deep because seeds are small and seedlings will be unable to reach the soil surface for development if buried too deeply. Smooth, firm seedbeds, with few large clods, can assist in maintaining uniformly shallow seeding (Murphy et al., 1976).

Seed clovers using an alfalfa drill or disk to prepare seedbed, broadcast seed, and use cultipacker or ringroller to incorporate seed (Bugg, pers. comm.). As recounted by Murphy et al. (1976), soil cover reduces depredations by birds and rodents, provides better moisture for imbibition and seedling development, and by reducing exposure to heat and sunlight ensures better survival of the rhizobia with which the seed may have been inoculated. Preceding crops of sudan grass or grain can reduce competition from weedy annual plants, and provides a firm seedbed. Clover seed can be sown directly into the stubble, with no further seedbed preparation and covered by using a ringroller. Alternatively, light disking can be used to cover seed. If the seed is not drilled, a roller or some type of drag should be used to cover the seed with soil. Where tillage is not feasible, a rangeland drill may be used (Murphy et al., 1976).

Seeding by early October, even into dry soil, leads to better establishment than November seedings. Cold reduces growth, and frost heave can push small clover plants out of the ground. Clovers compete best if they start growing simultaneously with resident annual plants (Murphy et al., 1976).

Clovers (Trifolium spp.) should be inoculated with Rhizobium trifolii (Nitragin Inoculant Types "B", "R", "O", or "WR" depending on the species of clover) (Nitragin Company, Inc., No Date). Survival of rhizobia is extended by use of coating materials that adhere the inoculant to the seed; nonetheless, sow within one day of inoculating (Weaver, 1988).

In the United States, most seed for Trifolium spp. is produced in the Northwest (Taylor, 1985). Flowering and seed production may be reduced by ungrazed, rank growth (Murphy et al., 1976).

Rincker and Rampton (1985) wrote that seed should contain less than 10% moisture if storage is to be for 1 year or longer. Moist seed lose viability rapidly. Rodents and other pests should, of course, be excluded.

Trifolium spp. are annual or perennial forbs; growth habit varies greatly among the various species (Bugg, pers. comm.)

Maximum height varies greatly among the various Trifolium spp. (Bugg, pers. comm.)

Most Trifolium spp. have simple taproots; some also have stolons or rhizomes that extend the life of the plant. The heavy root systems of clovers improve soil tilth and life, increase water-holding capacity, and deepen the soil to enhance drainage (Taylor, 1985).

The first year following seeding is critical for a clover stand. The stand should produce abundant seed to ensure perpetuation of the stand. Weed competition can be reduced through good seedbed preparation (Murphy et al., 1976).

Established clover does best when closely, continually grazed; this practice reduces rank growth and limits the number of foxtail and other grasses which can increase as soil N increases under clover (Murphy et al., 1976). Proper grazing and fertilization ensure self-perpetuating stands of adapted clovers. Clover pasture can be rotated with two successive crops of cereal grain or hay and then reseeded to clovers (Murphy et al. 1976).

Clovers grow better when mowed to 3 to 6 inches. Grasses tend to dominate if mowed to 6-12 inches (Murphy et al., 1976). Subclovers can be mown closely through the spring, whereas mowing of rose and crimson clover should cease when flower heads appear, to promote reseeding (C.A. Ingels, pers. comm.).

Most Trifolium spp. can be incorporated by disking or other standard methods of incorporation.

Harvest strategies typically represent compromises between delay to maximize yield and persistence and early harvest to maximize quality (Van Keuren and Hoveland, 1985). Mixtures of grasses and legumes give more consistent year-around production (Van Keuren and Hoveland, 1985).

The following account is from Bugg (pers. comm.) The usual range of implements for managing forage and green manure crops applies. Mowing equipment includes sickle-bar, rotary, and flail mowers. Appropriate tillage implements include disk, spring-toot, and spike-tooth harrows as well as power spaders. Combines are used for seed harvest.

Many Trifolium spp. are useful honey plants (Taylor, 1985).

Mixtures of grasses and legumes give more consistent year-around production (Van Keuren and Hoveland, 1985).

Kendall and Stringer (1985) reported that competition for sunlight is a major aspect in both intraspecific and interspecific dynamics, leading to domination of stands by clovers that express rapid regrowth or tall stature.

White and Scott (1991) in New York found that yield of cereal rye was less affected by living mulch of white clover, 'Ladino' clover, or red clover than of crown vetch, birdsfoot trefoil or alfalfa.

Clover above-ground dry biomass yields reported by Bugg et al. (1996) in Hopland, Mendocino County, during May following October seeding were (mean +/- S.E.M., Mg/ha): Berseem Clover ('Bigbee') 8.5+/-0.8; Crimson Clover ('Flame') 8.5+/- 1.5; Rose Clover ('Hykon') 6.2+/-1.7; 'Koala' Subclover, 9.7+/-1.6; 'Mt. Barker' Subclover 7.6+/-0.9; 'Seaton Park' Subclover 6.8+/-0.4; 'Dalkeith' Subclover 5.1+/-1.8; 'Trikkala' Subclover 8.3+/-1.4; Strawberry Clover ('Salina') 1.9+/-0.6; and White + Strawberry Clovers 3.9+/-0.9. Moraes et al. (1989) assessed dry matter yield, crude protein percentage, and in vitro dry and organic matter digestibilities for the native Brazilian clovers Trifolium riograndense Burkart (autotetraploid and diploid forms) and T. polymorphum Poir. were compared with white clover (T. repens L.) cultivars 'BR-1-Bage', 'Regal', 'Jacul', and 'Gualba.' The new varieties of white clover appeared promising. The native clovers showed low dry matter yield, but good quality, and appeared not to be cyanogenic.

N contribution varies greatly among the Trifolium spp.(Bugg, pers. comm.).

Non-N nutrient contributions are poorly investigated among the Trifolium spp. (Bugg, pers. comm.).

Trifolium spp. have widely-varying phenologies, rooting depths, water-use patterns, and drought tolerances (Bugg, pers. comm.).

Taylor (1985) wrote that forage crops like clovers protect soil from rain damage and reduce runoff, erosion, and pollution of surface waters.

Clovers confer many benefits to soils. Based on the account by Taylor (1985), the heavy root systems of clover: (1) make the soil mellow and supportive of root growth of succeeding plants; (2) enhance soil microbial life; (3) increase soil water-holding capacity; (4) reduce wind and water erosion of light soils and the baking of heavy soils; (5) increase soil permeability. Taylor (1985) also wrote that forage crops like clovers protect soil from rain damage and reduce runoff, erosion, and pollution of surface waters.

Taylor (1985) wrote that clovers contain from 60-80% (weight/weight) digestible dry matter. Van Keuren and Hoveland (1985) wrote that clover pasturage is beneficial for dairy and beef cattle and for horses. Clovers can also be used for hay, silage, and soilage (Van Keuren and Hoveland, 1985).

Manglitz (1985) wrote that insect pests attacking clovers include clover leaf weevil (Hypera punctata [Fabricius]), alfalfa weevil (Hypera postica [Gyllenhal]), alfalfa caterpillar (Colias eurytheme Boisduval), green cloverworm (Plathypena scabra [Fabricius]), omnivorous leaf tier (Cnephasia longana [Haworth]), various grasshoppers and crickets, various beetles, yellow clover aphid (Therioaphis trifolii Monell), pea aphid (Acyrthosiphon pisum [Harris]), blue alfalfa aphid (Acyrthosiphon kondoi Shinji), clover aphid (Nearctaphis bakeri [Cowen]), potato leafhopper (Empoasca fabae Harris), clover leafhopper (Aceratagallia sanguinolenta [Prov.]), meadow spittlebug (Philaenus spumarius [L.]), clover root curculio (Sitona hispidulus [Fabricius]), clover root borer (Hylastinus obscurus [Marsham]), clover head caterpillar (Grapholita interstinctana [Clemens]), lesser clover leaf weevil (Hypera nigrirostris [F.]), clover head weevil (Hypera meles [F.]), clover seed weevil (Tychius picirostris [Fabricius]), clover seed midge (Dasyneura legumnicola [Lintner]), and clover seed chalcid (Bruchophagus platypterus).

Insects can cause periodic local damage but do not usually eliminate the legume attacked; chemical control is usually impractical. In spring, various phytophagous mites can cause severe local damage. Along the Sierra foothills, a small leaftier caterpillar ties the folded clover leaf together with a web and lives inside, feeding on the leaf. Larvae of alfalfa weevil and clover leaf weevil (green, legless, and about 1/2 inch long) damage growing tips and young leaves in late spring (Murphy et al., 1976).

Leath (1985) noted that clovers have problems with plant-parasitic nematodes, including: (1) root knot nematodes (Meloidogyne spp.); (2) Root-lesion nematode (Praylenchus penetrans); (3) clover cyst nematode (Heterodera trifolii); (4) stem nematode (Ditylenchus dipsaci); (5) Xiphinema spp.; (6) Tylenchorhyncus spp.; and (7) Paratylenchus spp.

According to Leath (1985), clovers are afflicted with several diseases, including: (1) internal breakdown, a physiogenic disease that involves the deterioration of pith in the upper crown region; (2) 15 major diseases caused by fungal pathogens or complexes thereof; and (3) 15 diseases of minor importance, including those caused by fungal and bacterial pathogens. Barnett and Diachun (1985) list 19 classes of virus that affect clovers.

Murphy et al. (1976) detailed several important diseases of clovers. The causal agents of damping-off disease are the common soil-borne fungi Pythium spp. These usually attack young plants below the soil line, invade plant cells, and kill seedlings rapidly. Seed treatment does not protect small-seeded legumes; varietial and specific susceptibility varies.

Sclerotinia, a soil-borne fungal pathogen commonly termed water mold, leads to the appearance of dead, watery vegetation in scattered spots about 6 inches in diameter. This mainly occurs from late February through early April and is most severe in rank, ungrazed fields. The spots rapidly increase in size to several feet in diameter. A dense white mycelial web covers the dying clover. Within 10 days, small hard, black sclerotia (lumps of mycelium) appear on the soil surface. These look like large, irregularly shaped subclover seeds but are soft enough to cut open with a thumbnail and are white inside. With drying weather the disease disappears. A wide range of legumes is affected; treatment is impractical (Murphy et al., 1976).

Pepper spot (causal agent the fungus Pseudoplea trifolii) is common on clovers during February and March. Symptoms include black spots on leaflets and petioles. Severe infection causes the leaves to turn yellow, then brown, and the dead tissue is dotted with tiny black fruiting bodies of the fungus (Murphy et al., 1976).

Grazing keeps the faster-growing weeds and grasses from overtopping clover. Ideally, a new field should be kept grazed to about 3 inches until seed heads appear on the annual grasses. Thereafter, livestock feed selectively on clovers and should be removed from the range until clover seeds have matured (Murphy et al., 1976).

Field mice, kangaroo rats, and birds may deplete clover seed, threatening stand maintenance. Broadcast seeding without subsequent incorporation exposes seed to these seminivorous pests. Gophers and ground squirrels also destroy established plants. Trapping and baiting are sometimes worthwhile, but control of birds and insects is generally not possible (Murphy et al., 1976).