The common name is crimson clover (Duke, 1981; McLeod, 1982) or scarlet clover (Duke, 1981).

Trifolium incarnatum L. (Duke, 1981).

Duke (1981) listed the following as reseeding varieties of crimson clover: 'Dixie,' 'Auburn,' 'Chief,' and 'Talladega,' and 'Tibbee;' 'Frontier' is a soft-seeded variety. According to Knight (1985), five named reseeding cultivars have been used: 'Dixie,' 'Auburn,' 'Autauga,' 'Chief,' and 'Talladega;' the first three are mature about a week earlier than the last two. Cv 'Flame' has a higher proportion of hard seed, matures earlier, and produced more biomass than 'Dixie' (Baltensperger et al., 1987).

Crimson Clover has about 330,000 seeds/kg (Knight and Hoveland, 1985).

Hardseededness is a character that reduces the chance of premature germination and ensures self-reseeding. Among varieties of crimson clover, hardseededness can vary from 30-75% (Knight, 1985).

Five named reseeding cultivars have been used: 'Dixie,' 'Auburn,' 'Autauga,' 'Chief,' and 'Talladega.' The first three are mature about a week earlier than the last two (Knight, 1985).

'Flame' has a higher proportion of hard seed than 'Dixie' (Baltensperger et al., 1987).

Crimson clover shows good seedling vigor according to Slayback (pers. comm.).

MT Farm Williams (1956) noted that during establishment the force produced by legume seedlings may be crucial in overcoming the weight of overlying soil and surface crusts. Using glass tubes containing vermiculite and glass rods of known mass, the force produced by seeds of crimson clover, rose clover, subterranean clover, and alfalfa was estimated. Mean forces exerted (in g, + SEM) were estimated as follows. Alfalfa: 15.2 +/- 0.5 g; crimson clover: 23.8 +/- 0.2; rose clover 24.1 +/- 0.5; subterranean clover 60.0 +/- 2.9. The force exerted by the seeds was highly correlated (R=0.999) with seed weight, but not so highly (R=0.837) with hydrolyzable carbohydrates, suggesting that other factors may operate as well.

Williams (1963) conducted further studies on the penetrating force of emerging seedlings, which can be important in overcoming soil crusts and compaction and excessively-deep seeding. Crimson clover varieties showed great variability in the amount of force exerted by seedlings. 'Autauga' F.C. 32, 963 and Mississippi selection F.C. 32, 964 showed particularly great forces. These greatly exceeded those of rose clover, 'Caliverde' and 'Ranger' alfalfa, and 'Kenland' red clover. Forces exerted by crimson clover and alfalfa were highly dependent on temperature, with the maximum force attained for the former near 20o C, and for the latter between 25 and 30o C. These patterns suggest that plantings could be timed to achieve best emergence of seedlings.

Crimson clover is similar in appearance to rose clover but is a taller, more erect plant (Miller et al., 1989).

The showy crimson flower also distinguishes the crimson clover plant (Murphy et al., 1976; Finch and Sharp, 1983). The light-green foliage is covered with soft hairs; the leaves are usually unmarked but sometimes have a few dark-red spots; the plant branches less than does rose clover, and can grow to 1.5 ft. in height (Murphy et al., 1976).

Crimson clover flowers are self fertile but not self pollinating (Knight, 1985; Knight and Hoveland, 1985). Flowers produce much nectar and are heavily visited by various types of bees (Knight, 1985).

Crimson clover cannot tolerate extreme heat or cold and grows best during the cool, humid weather that typifies the winter in mild climates (generally south of New Jersey) (McLeod, 1982). It tolerates mean annual temperatures of from 5.9-21.3 degrees C, with the mean of 30 cases being 12.9 (Duke, 1981). Seedlings require considerable heat in the early stages of growth (McLeod, 1982). Crimson clover should be established 6 weeks before the average date of the first frost (Knight, 1985). Williams (1963) found that the forces exerted by crimson clover and alfalfa seedlings, which can be important in overcoming soil crusts, compaction, and excessively-deep seeding, were highly dependent on temperature, with the maximum force attained for crimson clover near 20o C, and for alfalfa between 25 and 30o C. These patterns suggest that plantings could be timed to achieve best emergence of seedlings. In establishing crimson clover, moisture tended to be limiting through November 1, with temperature the critical consideration thereafter, until mid-February (Knight, 1985).

According to Duke (1981), crimson clover is native to Atlantic and southern Europe, Caucasus and Transcaucasus. Knight and Hoveland (1985) maintain that it is native to southern Europe. It is assigned to the Mediterranean and Eurosiberian Centers of Diversity, is grown from the subtropical through cool temperate regions, and ranges from the Boreal Wet through Subtropical Moist Forest Life Zones (Duke, 1981). In Europe, it was cultivated for forage and green manure during the 18th century (Knight, 1985).

Crimson clover appears well-adapted to the predominant climatic conditions of the southeastern USA (Hargrove, 1986), and it tolerates a wide range of climatic and soil conditions (Knight, 1985).

Although Finch and Sharp (1983) stated that crimson clover is adapted to the same conditions as rose clover, Murphy et al. (1976) maintained that the former is not adapted over so wide a range of conditions.

Crimson clover tolerates from 3.1-16.3 dm (12.2-64.2 inches) of annual precipitation, with the mean of 30 case being 9.2 Duke, (1981) and grows well in regions with 8.89 dm (35 inches) or more annual rainfall (McLeod, 1982). It cannot endure much drought (McLeod, 1982) and likewise does not do well on poorly-drained soils (Duke, 1981; Knight and Hoveland, 1985). Moist soil is essential for germination and establishment (McLeod, 1982). In California, crimson clover will reseed only under excellent moisture conditions (Miller et al., 1989), i.e., with moisture at least throughout April (Murphy et al., 1976).

In establishing crimson clover, moisture tended to be limiting through November 1, with temperature the critical consideration thereafter, until mid-February (Knight, 1985).

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. Sweet clover showed intermediate values.

Crimson clover is adapted to soils of low fertility, and has an intermediate lime requirement; on infertile sites, phosphate and potash fertilizers and manure may increase production (McLeod, 1982). A fall application of 200-400 kg/ha of 0:20:20 N:P:K fertilizer may suffice for two years on infertile sites (Duke, 1981).

Crimson clover is tolerant of alkaline soils and of a pH range of 4.8-8.2, with the mean of 26 cases being 6.5 (Duke, 1981). Slayback (pers. comm.) suggested a pH range of 5.5 to 7.0. Crimson clover is intolerant of poorly-drained calcareous soils (Knight and Hoveland, 1985), and muck or extremely acid soils do not support good growth (McLeod, 1982).

Crimson clover tolerates a wide range of soil conditions (Knight, 1985) but does not do well on calcareous soils or with poor drainage (Knight and Hoveland, 1985). Duke (1981) wrote that crimson clover or varieties thereof are noted for tolerance of high pH, heavy soil, and sand, thriving on sand or clay soils, so long as drainage is good. McLeod (1982) stated that the species will grow on almost any soil, provided it is well-drained, but said that best growth occurs on loam soils with a good humus content. Soils that are cold or waterlogged during the winter are not suitable (Duke, 1981) nor are muck or extremely acid soils (McLeod, 1982). Other recommendations on suitable soil types include: sandy loam to clay loam (Slayback, pers. comm.), clay or sandy soil (Murphy et al., 1976; Knight and Hoveland, 1985); and Ultisols (Hargrove, 1986). Pears et al. (1989) stated that crimson clover appears well-adapted to on sandy loam soils and does not do well on heavy soils.

According to McLeod (1982), crimson clover withstands shade. It is a self-reseeding component of understory cover crops in orchards and vineyards in California and in pecan orchards in southern Georgia. This suggests some tolerance of shade (Bugg, pers. comm.).

White and Worsham (1990) evaluated eight herbicide treatments for hairy vetch and another eight for crimson clover under no-till management preceding corn and cotton. Preceding cotton, the treatments were: (1) Paraquat, (2) Paraquat + 2,4-D, (3) Paraquat +cyanazine, (4) Glyphosate, (5) Glyphosate + 2,4-D, (6) Glyphosate + cyanazine, (7) 2,4-D, (8) Cyanazine. Preceding corn, the treatments were (1) Paraquat, (2) Paraquat + 2,4-D, (3) Paraquat + dicamba, (4) Glyphosate, (5) Glyphosate + 2,4-D, (6) Glyphosate + dicamba, (7) 2,4-D, (8) Dicamba. Paraquat alone of in combination with dicamba, 2,4-D or cyanazine, and cyanazine alone were the best controls for crimson clover. Glyphosate alone was relatively ineffective at controlling hairy vetch in corn; all other treatments were effective against hairy vetch in corn. In cotton, the only treatments that worked well against hairy vetch were 2,4-D or cyanazine alone or combined with glyphosate.

Based on relay-intercropping trials in southern Georgia, crimson clover appears susceptible to glyphosate (Round-up) (Bugg, pers. comm.). Paraquat (0.6 kg ai/ha) and HOE-39866 (0.8 kg ai/ha) gave control of crimson clover and hairy vetch regardless of the date of application (Griffin and Dabney, 1990).

Duke (1981) termed crimson clover a stout, soft-pubescent winter annual. Seed should be sown from mid July until November, with early seeding more important in northern sectors; spring plantings usually result in stunting, poor flowering, and low seed yields (Duke, 1981). Crimson clover grows in the winter but puts on most of its growth in the spring, maturing in May (Finch and Sharp, 1983). Flowering is induced when daylength exceeds 12 hours (Knight, 1985). The flowers are self fertile but not self pollinating (Knight, 1985; Knight and Hoveland, 1985), produce much nectar, and are heavily visited by various types of bees (Knight, 1985).

Seeding rates have been variously suggested as 9 lbs/acre (Finch and Sharp, 1983); 12-15 kg/ha (10.7-13.4 lbs/acre) (Duke, 1981); 15 to 20 lbs/acre (Miller et al., 1989); 15-30 lbs/acre (McLeod, 1982); and 40-50 lbs/acre for unhulled seed (McLeod, 1982).

Crimson clover can be grown in conjunction with rye, vetches, annual ryegrass, and various cereals. When sown in combination with companion crops, crimson clover is usually sown at 2/3 the normal rate, and the other crop at 1/3 the monocultural rate. Developmental rates of annual ryegrass and tall fescue are similar to that of crimson clover (Knight, 1985).

Recommendations for sowing depth include 1/2 inch (McLeod, 1982), 1.3 cm (0.5 inch) on clay soils, and 2 cm (0.79 inch) on sandy soils (Duke, 1981).

Duke (1981) suggested a firm seedbed (see: McLeod, 1982; Finch and Sharp, 1983) and broadcasting or drilling; drilling produces a better stand than broadcasting (Duke, 1981; McLeod, 1982). If seed are drilled, spacing between plants should be about 2.5 cm (1 inch). Natural, unhulled seed germinates better than hulled, according to McLeod (1982).

Crimson clover can be grown in combination with cereal grains, annual ryegrass, and other winter annual legumes. It can also be established in existing stands of bermudagrass, dallisgrass, johnsongrass, bahiagrass, or sericea lespedeza (Knight and Hoveland, 1985).

Before overseeding into existing grass sod, grass must be mowed closely to allow seedlings to establish. Light disking can also reduce competition by grasses (Knight, 1985).

Duke (1981) stated that seeding can occur from July until November, with early seeding being important in northern sectors. The aim of early sowing is to ensure that plants are well established before freezing weather occurs; frost heaving is especially damaging to young plants (Knight and Hoveland, 1985). In fact, crimson clover should be established 6 weeks before the average date of the first frost (Knight, 1985). However, July sowing can result in stand failure due to virus (Knight, 1985). In Mississippi, August 15 planting led to the highest yields (Knight, 1985). In establishing crimson clover, moisture tended to be limiting through November 1, with temperature the critical consideration thereafter, until mid-February (Knight, 1985).

For California, fall seeding is suggested (Finch and Sharp, 1983). Slayback (pers. comm.) specified that September-October seeding dates are best and that spring sowing for summer production necessitates irrigation. Spring seeding often results in stunting, poor flowering, and reduced seed yield (Duke, 1981). Despite its natural winter-annual growth habit, in the Far North, crimson clover can be spring sown and grown as a summer crop, as is done in rotation with potatoes in Maine (McLeod, 1982).

Crimson clover requires rhizobial inoculant type "R" (Nitragin Co.) (Burton and Martinez, 1980; Duke, 1981).

Crimson clover seed cost is low (Bugg, pers. comm.).

Crimson clover seed availability is fair to good (Slayback, pers. comm.).

Flowering is induced when daylength exceeds 12 hours (Knight, 1985). In California, crimson clover flowers from May through August, according to Munz (1973). Cvv 'Dixie' and 'Frontier' are among the earliest to head out and set seed (Morey and Marchant, 1977), but cv 'Flame' flowers still earlier (about 2 weeks) (Baltensperger et al., 1987).

Crimson clover was considered early maturing by Finch and Sharp (1983), and will set seed by late May (Finch and Sharp, 1983; Miller et al. 1989).

Cv 'Flame' matures 2 weeks earlier than 'Dixie' (Baltensperger et al., 1987).

Crimson clover reseeds well when allowed to mature (McLeod, 1982). This has been seen in in vineyards in Del Rey (east side of the southern San Joaquin Valley, California) (Masumoto, pers. comm.).

However, reseeding requires moisture at least through April, as recounted by Murphy et al. (1976). The seedheads are easily accessible for use by grazing animals, and removal of all seed-producing heads must be prevented if reseeding is to be assured (Murphy et al. 1976).

Duke (1981) listed seed yields as commonly ranging from 340-410 kg/ha, with higher values on soils of intermediate as opposed to high fertility. Maximum seed yields are in the range of 1,000-1,200 kg/ha (Knight and Hoveland, 1985).

According to Duke (1981), seed can be harvested in three ways: (1) combine standing plants; (2) mowed and left to swath or windrowed to dry and later threshed with a combine; or (3) mowed, swathed, or windrowed to dry, then hauled to a stationary huller or thresher. Hulls should be dark brown if seed is to be combined directly, light brown if mowed.

The seed has intermediate longevity (McLeod, 1982).

Crimson clover is a stout, soft-pubescent annual legumes; stems are erect (Duke, 1981).

Crimson clover can grow to 18 inces in height (Murphy et al. 1976) or, according to Finch and Sharp (1983), to between 12 and 16 inches. Height of cv 'Flame' grown in Hopland, Mendocino County, California, was 48.90+/-15.77 cm (19.25 +/- 6.21 inches) (Mean +/- S.E.M.) (Bugg et al., unpublished data).

The root system is simple, dominated by a taproot, and often well nodulated (Bugg, pers. comm.).

Kutschera (1960) reported that crimson clover generally roots to a depth of 31-55 cm.

In establishing crimson clover, moisture tended to be limiting through November 1, with temperature the critical consideration thereafter, until mid-February (Knight, 1985). It should be established 6 weeks before the average date of the first frost (Knight, 1985), but July sowing can result in stand failure due to virus (Knight, 1985). For early sowing, frequent late summer and early fall rainfalls are required so the plants can get a good start (McLeod, 1982). On the other hand, the species requires considerable heat in the early stages of growth (McLeod, 1982).

Crimson clover can be overseeded into existing grass sod, but grass must be mowed closely to allow seedlings to establish. Light disking can also reduce competition by grasses (Knight, 1985).

During establishment, the force produced by legume seedlings may be crucial in overcoming the weight of overlying soil and surface crusts. Using glass tubes containing vermiculite and glass rods of known mass, the force produced by seeds of crimson clover, rose clover, subterranean clover, and alfalfa was estimated. Mean forces exerted (in g, + SEM) were estimated as follows. Alfalfa: 15.2 + 0.5 g; crimson clover: 23.8 + 0.2; rose clover 24.1 + 0.5; subterranean clover 60.0 + 2.9. The force exerted by the seeds was highly correlated (R=0.999) with seed weight but not so highly (R=0.837) with hydrolyzable carbohydrates, suggesting that other factors may operate, as well (Williams, 1956).

Crimson clover varieties that reseed include 'Dixie,' 'Auburn,' 'Chief,' and 'Talladega,' and 'Tibbee' (Duke, 1981; Knight, 1985). The first three are mature about a week earlier than the last two (Knight, 1985). 'Frontier' is a soft-seeded variety (Duke, 1981). Hardseededness is a character that avoids premature germination and ensures self-reseeding; among varieties of crimson clover, hardseededness can vary from 30-75% (Knight, 1985). Cv 'Flame' shows better biomass production, earlier maturation, higher percentage of hard seed, and better stand persistence than do the cultivars previously named (Baltensperger et al., 1987). Liming and additions of P and K may be needed to maintain productive stands (Duke, 1981).

Crimson clover can be overseeded into existing grass sod, but grass must be mowed closely to allow seedlings to establish. Light disking can also reduce competition by grasses (Knight, 1985). Once established, crimson clover should be mowed no closer than 3 to 5 inches (Finch and Sharp, 1983; Miller et al. 1989), allowing 3 to 4 weeks regrowth before maturity (Finch and Sharp, 1983). Such mowing can improve growth (McLeod, 1982) and reduce lodging (Knight, 1985).

Crimson clover produces flowers at the ends of stems; therefore, grazing must be regulated to keep animals from removing all the flowers (Murphy et al., 1976).

For best results as a green manure, crimson clover should be plowed down 2-3 weeks before the succeeding crop; strip-tillage schemes are also used, whereby row crops are planted in the tilled strips and the crimson clover in the intervening strips allowed to produce seed for harvest and residue serves as mulch (Duke, 1981). McLeod (1982) stated that the residue decomposes rapidly when turned under.

House (1989) reported a replicated trial in which corn was grown following no-till or conventionally-tilled winter cover crops of hairy vetch, crimson clover, or wheat. Hairy vetch harbored a more abundant and diverse below-ground arthropod fauna (herbivores and predators) than did crimson clover or wheat. Elateridae, Curculionidae, and Carabidae were particularly abundant following no-till hairy vetch. Scarabaeidae were especially abundant following conventionally-tilled crimson clover. Elateridae (wireworms) were the dominant herbivores in no-till systems. Observed faunal differences had dissipated by July.

Seed may be combined from standing plants, mowed and swathed or windrowed to dry, and then hulled or threshed with either a combine or stationary machines (Duke, 1981).

Normal mowers, combines, threshers, and tillage implements are appropriate in managing crimson clover; no expensive machinery is needed (Duke, 1981).

Crimson clover is the most important winter annual legume in the Southeast; it is excellent for pasture, hay, or green manure and at protecting the soil during winter and spring (Duke, 1981; and see McLeod, 1982). It can be winter grown as a green manure in rotation between milo and cotton, for example, or soybeans, small grain, and cotton (McLeod, 1982).

As recounted by Murphy et al. (1976), it is often used as a hay crop or for roadside plantings as well as for range seeding. It is best suited for short-rotation planting, for use in a mixture with grains, or as a rotation crop with grains, and it is sometimes cut for hay. The seedheads are easily accessible for use by grazing animals.

Crimson clover is a good green-manure crop for pecan and other orchard crops and can also be used in agroforestry, double-cropping, and no-till farming systems (Knight and Hoveland, 1985).

In Georgia, crimson clover can be a self-reseeding cover crop in pecan, peach, and other orchards (Knight, 1985). In Alabama, it has been used to improve the soil for cotton (Knight, 1985).

Crimson clover can be overseeded into existing grass sod, but grass must be mowed closely to allow seedlings to establish. Light disking can also reduce competition by grasses (Knight, 1985).

As detailed by Knight (1985), crimson clover can be grown in conjunction with rye, vetches, annual ryegrass, and various cereals. When sown in combination with companion crops, crimson clover is usually sown at 2/3 the normal rate, and the other crop at 1/3 the monocultural rate. Developmental rates of annual ryegrass and tall fescue are similar to that of crimson clover.

Crimson clover can be grown in combination with cereal grains, annual ryegrass, and other winter annual legumes. It can be established in existing stands of bermudagrass, dallisgrass, johnsongrass, bahiagrass, or sericea lespedeza (Knight and Hoveland, 1985). In Georgia, crimson clover can be a self-reseeding cover crop in pecan, peach, and other orchards (Knight, 1985). Crimson clover can be seeded with subclover or black medic (Finch and Sharp, 1983).

Williams (1963) evaluated pure plantings and in 1:1 bicultures of a S. Australian commercial strain of crimson clover, rose clover (T. hirtum All., strain S.6), and subterranean clover (T. subterraneum L. cv 'Bacchus'). Competition for light was assessed in relation to leaf area and leaf position in the canopy. Leaf area in 4-cm horizontal strata, leaf weight, shoot weight production, and light penetration through canopies were measured at intervals during the vegetative phase (i.e., through 99 days after sowing). Crimson and rose clovers held apparent initial advantages over subterranean clover in terms of light-absorbing surface area of cotyledons and first unifoliate leaves and because these leaves were elevated further from the soil surface. However, this situation changed with time. In paired sowings, crimson and subterranean clover became equally dominant over rose clover, while subterranean clover overtopped crimson despite the greater total leaf area of the latter. The most productive mixture (crimson clover + subterranean clover) was no more productive that the best species (crimson clover) in monoculture. Competition has other dimensions than those reported here, including the advantage conferred by hardseededness of rose clover, which enables it to dominate polyspecific stands following droughts that kill seedlings of the other two clovers.

Subterranean clover has, on the average, larger seed than does crimson clover, and plot studies by Williams, Black, and Donald (1968) indicated that the former will tend to dominate in mixtures due to more rapid early growth and shading of the crimson clover. When larger seeds of crimson clover were selected and interseeded with smaller seeds of subterranean clover, the pattern was reversed. Crimson clover was not eliminated from any of the mixtures evaluated.

Ranells and Wagger (1997b) conducted a replicated field trial on N-dynamics of the following monocultural and bicultural cover crops: (1) cereal rye; (2) crimson clover; (3) hairy vetch; (4) cereal rye/crimson clover; and (5) cereal rye/hairy vetch. Cereal rye grown without legume (in monoculture) contained 11.2 and 11.1 (two years of data) kgN/ha when grown with low residual soil N (prior corn fertilized using 150 kgN/ha). The corresponding values for cereal rye grown with crimson clover were 12.3 and 12.3 and with hairy vetch, 19.9 ad 15.3 kgN/ha. With high residual N (300 kgN/ha) applied to preceding corn crop), results were qualitatively similar, with statistically significant differences obtained in 1993 as follows: rye (11.3 kgN/ha) < rye (with crimson clover-18.2 kgN/ha) < rye (with hairy vetch-26.5 kgN/ha). These results occurred while the corresponding figures for cereal rye biomass in Mg/ha were 5.73 > 3.26 > 2.27. Cereal rye monocultures reduced residual soil N by 62 and 37% in 1993 and 1994. Bicultures with cereal rye and legumes reduced residual soil N by 44 and 15% for the same years. Taken together, these values strongly suggest transfer of N from legumes to associated cereal rye, because the cereal rye was sown at lower densities and attained equal or lower biomass in biculture, yet accumulated higher total N than in cereal rye monocultures.

In North Carolina, Ranells and Wagger (1997) reported a replicated trial on recovery of potassium nitrate labeled with 10 atom % N-15 by monocultures of cereal rye and crimson clover and a biculture of the two. Above-ground dry matter production through time was as follows (data given for two successive years).

Above-ground N accumulation through time was as follows (data given for two successive years):

Above-ground C:N ratios through time were as follows (data given for two successive years).

Duke (1981) reported that crimson clover hay yields average from 4.5-5.0 Mg/ha, with yields as high as 7.5 Mg/ha on exceptional soils. Smith et al., (1987.) summarized dry matter yields (Mg/ha) obtained in individual studies: 2.4, 4.5, 5.0, 5.3, 6.7, 3.2. Hargrove (1982) reported that dry matter production averaged 3,364 lbs/acre/yr., but mean dry weight of three year field trial in Georgia was 7.17 Mg/ha, exceeding production of of other cover crops (Hargrove, 1986). On a high-fertility site in Hopland, Mendocino County, California, dry above-ground biomass of cv 'Flame' was 8.5+/-1.5 Mg/ha, Mean +/-S.E.M.; when weeds were included, biomass was 9.1+/-1.5 Mg/ha, (Mean +/- S.E.M.) (Bugg et al., unpublished data).

In North Carolina, Ranells and Wagger (1997) reported a replicated trial on recovery of potassium nitrate labeled with 10 atom % N-15 by monocultures of cereal rye and crimson clover and a biculture of the two. Above-ground dry matter production through time was as follows (data given for two successive years).

Above-ground N accumulation through time was as follows (data given for two successive years):

Above-ground C:N ratios through time were as follows (data given for two successive years).

Duke (1981) reported that crimson clover hay yields average from 4.5-5.0 Mg/ha, with yields as high as 7.5 Mg/ha on exceptional soils. Based on Duke's (1981) report of 16.7% N on a dry-matter basis, and the assumption that 6.5% of this is N, these biomass yields project to N contents of 48.85-54.28 kg N/ha with peak values of 81.41 kg N/ha. Above-ground biomass data from Hopland, Mendocino County, California, collected by Bugg et al. (Unpublished data) project to 91.79 +/- 16.03 kg N/ha (cv 'Flame'). Studies in Georgia by Hargrove (1982), during 1976-77, showed that for fluted coulter planted corn following crimson clover no response was obtained to an additional 105 lbs of N/acre. Crimson clover dry matter production averaged 3,364 lbs/acre/yr, and the tissue contained 71 lbs of nitrogen/acre/yr. Hargrove (1982) calculated that based on dry matter tields and N content: 1.1 tons/acre at 2.4% translated to 53 lbs N/acre.Hargrove (1986) later found that crimson clover can replace as much as 120 kg fertilizer N/ha (no-till grain sorghum trials in Georgia) although the mean N content of three year field trial in Georgia was 170 kg/ha. In terms of total N content, crimson clover tended to be superior to other leguminous cover crops due to its large dry matter production. The mean N content of crimson clover was significantly greater than that of subterranean clover and common vetch but not significantly greater than that of hairy vetch (Hargrove, 1986).

Smith et al. (1987) summarized aboveground nitrogen contents (kg/ha) obtained in individual studies as: 133, 56, 170. Proportion of nitrogen estimated obtained from fixation were given as: 0.79, 0.36, 0.78. Estimated N fertilizer equivalences under no-tillage regimes were given (kg/ha): followed by cotton - 34-67, 68; followed by corn - 67, 50 or less, 100,19-128; followed by sorghum - 89 or less, 50 - 128.

Smith et al. (1987) also gave aboveground nitrogen contents (kg/ha) obtained in mixture with rye as 147, with the proportion of nitrogen estimated obtained from fixation being 0.69. Proportion of nitrogen accumulated in roots was given as 0.12.

In a study of corn and sorghum production in Georgia by McVay et al. (1989), crimson clover had an above-ground N-content of 108 kg/ha and replaced 99 kg/ha of N. Bermuda grass grown following crimson clover receives 120-240 kg/ha of N from crimson clover residue (Knight and Hoveland, 1985). Crimson clover can provide 75 to 100 kg/ha of N to succeeding corn. (Knight, 1985).

Ranells and Wagger (1996) found that, based on linear correlation coefficients, initial C:N ratio was a consistently significant predictor of N release by cover crop residues (cereal rye, crimson clover, hairy vetch, and bicultures of cereal rye/crimson clover and cereal rye/hairy vetch). By contrast, Lignin:Nitrogen ratio was not a reliable predictor of N release, although this has been the case in prior studies.

In a replicated field study, Ranells and Wagger (1997a) explored N-recovery by cereal rye and crimson clover monocultures, bicultures of these two plants, and a weedy fallow on the coastal plain of North Carolina. 15N-labelled potassium nitrate fertilizer was applied to microplots 1 week after sowing cover crops (sowing in early October) in a Norfolk loamy sand. Rooting depth was 25 cm in December, 70 cm in March, and 90 cm in April. Percent recovery of fertilizer N by various cover crop regimes was as follows:

Significance tests (Fisher's plsd) indicated the following ranking for efficiency of fertilizer N recovery: cereal rye > cereal rye/crimson clover > crimson clover = resident winter-annual weeds.

Ranells and Wagger (1996) conducted field trials on the North Carolina coastal plain concerning monocultures of crimson clover, hairy vetch, and cereal rye, and bicultures of crimson clover/cereal rye and hairy vetch/cereal rye managed without tillage. The greatest N-content occurred with hairy vetch monocultures (154 kg N/ha) and the least with cereal rye (41 kg N/ha). The rates of N-release were in this order: hairy vetch > crimson clover = hairy vetch/cereal rye > crimson clover/cereal rye = cereal rye. For cereal rye grown in monoculture, the C:N ratio was 40:1, whereas when cereal rye was grown in biculture with hairy vetch, the C:N ratio was 28:1. Thus, cereal rye grown with hairy vetch has less likelihood of immobilizing N during decomposition. Mean values obtained for this two-year study were as follows:

In this tillage experiment, growth stages were as follows, on April 19 or 20.

In the warm, rainy first year of the study, 90% of the N in the hairy vetch monoculture had been released by the 8th week of the study; 71% of the N had been released for the cereal rye monoculture.

Quemada and Cabrera (1995a) reported the following:

These data for residues left on the soil surface reflect the slower breakdown of stems, and the immobilization of N caused by application of materials with high C/N ratios.

Quemada and Cabrera (1995a) also evaluated the relative allocation of carbon to soluble compounds, cellulose, hemicellulose, and lignin, which have profoundly differing rates of decomposition, with the list given in descending order of rate of breakdown. For all three plant species mentioned, stems had much higher concentrations of lignin than did leaves.

Using the CERES-N submodel, Quemada and Cabrera (1995b) further explored the release of N from no-till cover crop residues, deriving decay rate constants from breakdown rates for stems, leaves, and mixtures of both. The constants that best fitted the data were 0.14-day for cellulose; decay rate for lignin was assumed to be 0.00095-day. That is each day, more than 10% of the soluble carbohydrate pool degrades to CO2, about 0.34% of the cellulose pool degrades, and less than 0.1% of the lignin.

Quemada and Cabrera (1995b) in Georgia used the CERES-N model to predict conditions for leaves or stems or 50:50 by dry weight mixtures of crimson clover, cereal rye, oat, and wheat harvested at maturity. All crop residue was cut into 1-cm pieces and placed atop sandy loam soil that had previously been managed without tillage. Incubation was in acrylic plastic cylinders at 35° and 98% RH, for 160 days. The study was replicated three times. Observed N-mineralization was slower than previously reported for incorporated residues:

Humus native to the soil was estimated to mineralize N at 0.00042/day.

Reported C/N ratios were:

 

Ranells and Wagger (1992) in the North Carolina Piedmont reported that N release rate from crimson clover residues managed without tillage was dependent on the growth stage at which the plant was killed (using glyphosate [Round Up®] herbicide). After 16 weeks of decomposition, %N release and total cumulative N release for crimson clover residues were as follows (means of two years):

These authors also provide detailed chemical profiles of the crimson clover at different stages and for two successive years indicating the progressive increase of lignin, hemicellulose, and cellulose, and the increase of C:N ratio as the plant matures from late vegetative state to seed set. Concomitantly, biomass of the cover crop (Mg/ha) and N content (kgN/ha) increase while N concentration (g/kh) decreases. Based on these studies, Ranells and Wagger (1992) recommended killing the crimson clover at late bloom stage to maximize N release.

Ranells and Wagger (1997b) conducted a replicated field trial on N-dynamics of the following monocultural and bicultural cover crops: (1) cereal rye; (2) crimson clover; (3) hairy vetch; (4) cereal rye/crimson clover; and (5) cereal rye/hairy vetch. Cereal rye grown without legume (in monoculture) contained 11.2 and 11.1 (two years of data) kgN/ha when grown with low residual soil N (prior corn fertilized using 150 kgN/ha). The corresponding values for cereal rye grown with crimson clover were 12.3 and 12.3 and with hairy vetch, 19.9 ad 15.3 kgN/ha. With high residual N (300 kgN/ha) applied to preceding corn crop), results were qualitatively similar, with statistically significant differences obtained in 1993 as follows: rye (11.3 kgN/ha) < rye (with crimson clover-18.2 kgN/ha) < rye (with hairy vetch-26.5 kgN/ha). These results occurred while the corresponding figures for cereal rye biomass in Mg/ha were 5.73 > 3.26 > 2.27. Cereal rye monocultures reduced residual soil N by 62 and 37% in 1993 and 1994. Bicultures with cereal rye and legumes reduced residual soil N by 44 and 15% for the same years. Taken together, these values strongly suggest transfer of N from legumes to associated cereal rye, because the cereal rye was sown at lower densities and attained equal or lower biomass in biculture, yet accumulated higher total N than in cereal rye monocultures.

In North Carolina, Ranells and Wagger (1997) reported a replicated trial on recovery of potassium nitrate labeled with 10 atom % N-15 by monocultures of cereal rye and crimson clover and a biculture of the two. Above-ground dry matter production through time was as follows (data given for two successive years).

Above-ground N accumulation through time was as follows (data given for two successive years):

Above-ground C:N ratios through time were as follows (data given for two successive years).

Quemada and Cabrera (1995a) in Georgia found that chemical composition of various winter-annual plants varied in their chemical composition and in their decomposition rates when managed without tillage. In addition, leaves consistently varied from stems in having greater C/N ratios and lignin and cellulose contents (the latter two expressed as g/kg of plant material). Based on CO2 emissions and N mineralized, stems decomposed more slowly than leaves for crimson clover, cereal rye, wheat, and oat.

Clover dry matter production averaged 3,364 lbs/acre/yr., and the tissue contained 5 lbs of P/acre and 90 lbs of K/acre (Hargrove, 1982).

Ranells and Wagger (1996) cited Van Soest (1964) as a reference for the statement that lignia linkages in non-leguminous plants are usually more resistant to decomposition than those of legumes. Ranells and Wagger observed that, based on field trials in North Carolina, lignia concentrations were significantly greater for hairy vetch (84g/kg) than for cereal rye (27g/kg) or crimson clover (46g/kg) (Least Significant Difference=11).

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. Sweet clover showed intermediate values (Zachariassen and Power, 1991).

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. Sweet clover showed intermediate values (Zachariassen and Power, 1991).

Compared to an adjacent area under conventional tillage management, soil organic carbon and organic nitrogen levels were much higher in no-till crimson clover winter cover crop plots at the conclusion of the study (Hargrove, 1982).

Ranells and Wagger (1997b) conducted a replicated field trial on N-dynamics of the following monocultural and bicultural cover crops: (1) cereal rye; (2) crimson clover; (3) hairy vetch; (4) cereal rye/crimson clover; and (5) cereal rye/hairy vetch. Cereal rye grown without legume (in monoculture) contained 11.2 and 11.1 (two years of data) kgN/ha when grown with low residual soil N (prior corn fertilized using 150 kgN/ha). The corresponding values for cereal rye grown with crimson clover were 12.3 and 12.3 and with hairy vetch, 19.9 ad 15.3 kgN/ha. With high residual N (300 kgN/ha) applied to preceding corn crop), results were qualitatively similar, with statistically significant differences obtained in 1993 as follows: rye (11.3 kgN/ha) < rye (with crimson clover-18.2 kgN/ha) < rye (with hairy vetch-26.5 kgN/ha). These results occurred while the corresponding figures for cereal rye biomass in Mg/ha were 5.73 > 3.26 > 2.27. Cereal rye monocultures reduced residual soil N by 62 and 37% in 1993 and 1994. Bicultures with cereal rye and legumes reduced residual soil N by 44 and 15% for the same years. Taken together, these values strongly suggest transfer of N from legumes to associated cereal rye, because the cereal rye was sown at lower densities and attained equal or lower biomass in biculture, yet accumulated higher total N than in cereal rye monocultures.

Crimson clover is an excellent pasture and hay crop (Duke, 1981). Use in mixture with grass reduces the danger of bloat (Knight, 1985), which seldom occurs with crimson clover (Duke, 1981).

No specific information is available; the plant is very attractive to bees, which might annoy or sting workers (Bugg, pers. comm.).

Flowers of crimson clover are attractive to bees (Pears et al., 1989).

In California, crimson clover flowers contain abundant minute pirate bug (Orius tristicolor), an important beneficial insect that preys on various agricultural pests (Bugg, pers. comm.).

In southern Georgia, crimson clover was found to sustain pea aphid (Acyrthosiphon pisum [Harris]) and blue alfalfa aphid (Acyrthosiphon kondoi Shinji) which do not attack pecans. They were found along with associated predators that can disperse to pecan trees and attack pecan aphids. Crimson clover is being used by some pecan growers in efforts to enhance early-season biological control of pecan aphids (Bugg et al., 1990a).

House and Alzugaray (1989) reported that hairy vetch (Vicia villosa Roth) sustained higher densities of above-ground arthropods and a more taxonomically-diverse entomofauna than did crimson clover (Trifolium incarnatum L.) or wheat (Triticum aestivum L.). Soil arthropods were more diverse under no-tillage than under tillage. Pest and beneficial soil arthropods were most abundant in no-tillage corn preceded by hairy vetch. Differences that were apparent early had dissipated by midseason.

Bugg et al. (1991a) reported on a study in southern Georgia on cool- season cover crops relay intercropped with spring plantings of cantaloupe (Cucumis melo L. var. reticulatus Seringe) in efforts to enhance biological control of insect pests on the latter. Eight cover-crop regimes were tested in a replicated trial: (1) A hybrid vetch, Vicia sativa L. X V. cordata Wulf (Fabaceae, cv 'Vantage'); (2) Common lentil, Lens culinaris L. (Fabaceae, cv 'Chilean 78'); (3) Subterranean clover, Trifolium subterraneum L. (Fabaceae, cv 'Mt. Barker'); (4) Crimson clover, Trifolium incarnatum L. (Fabaceae, cv 'Dixie'); (5) Rye, Secale cereale L. (Poaceae, cv 'Wrens Abruzzi'); (6) Mustard, Brassica hirta Moench (Brassicaceae, cv 'Florida Broadleaf'); (7) Polyculture of the six crops just mentioned; and (8) A control which received no seeds but was otherwise treated similarly to other regimes. Significant differences due to cover crop were obtained for densities of the generalist predator Geocoris punctipes (Say) (Hemiptera: Lygaeidae) (a bigeyed bug) amid cover crops, their residues, or weeds; on or near cantaloupe plants; and on or near sentinel egg masses of fall armyworm, Spodoptera furgiperda (J. E. Smith) (Lepidoptera: Noctuidae) pinned to cantaloupe leaves. No significant effect due to cover crop was found for proportions of of egg masses occupied or damaged by predators. In all four cases, absolute responses were highest for the plots of subterranean clover. Among those regimes attaining good stands of cover crops, numbers of G. punctipes per sentinel egg mass were significantly greater for the subterranean clover regime than for rye, crimson clover, polyculture but not than TVantageU vetch. Rye was particularly poor habitat for G. punctipes.

Bugg et al. (1990a) reported on a trial in southern Georgia that concerned 20 cover-cropping regimes and associated insects. Convergent lady beetle (Hippodamia convergens Guerin-Meneville]) and seven-spotted lady beetle (Coccinella septempunctata [L.]) first were found in substantial numbers on rye, then on crimson clover (which harbored pea aphid [Acyrthosiphon pisum {Harris}]) and lentil, later on subterranean clover, still later on narrow-leafed lupin, then hairy vetch, and lastly on mustard and collard. Lygus spp., which are important pests of field, row, and orchard crops, were exceptionally abundant on 'Cahaba White' and 'Vantage' vetches; both feature stipular extrafloral nectaries at which Lygus frequently fed. Lygus were also abundant on hairy vetch (monoculture and biculture) and to a lesser extent on turnip and monocultural crimson clover but were notably scarce on subterranean clover.

Field trials in southern Georgia by Bugg et al. (1990b) indicated that during April and early May Lygus lineolaris (Palisot de Beauvois) (tarnished plant bug) attained relatively-high densities on the hybrid vetch (cvv 'Cahaba White' or 'Vantage'), lower levels on crimson clover and lentil, and particularly-low densities on 'Mt. Barker' subterranean clover. Low densities were also obtained on 10 other varieties of subterranean clover. Late-instar and adult tarnished plant bug lived longer when caged on crimson clover than on hybrid vetch, which in turn supported better survival than did subterranean clover. When adults of tarnished plant bug were caged on hybrid vetch or subterranean clover with or without floral and fruiting structures, there was no evidence that the presence of these structures prolonged tarnished plant bug survival on either crop. In choice tests with flowering and fruiting sprigs of three cover crops, tarnished plant bug preferred crimson clover over hybrid vetch, which in turn was more attractive than subterranean clover. When sprigs were presented after reproductive structures had been excised, there was no statistically-significant preference by tarnished plant bug. Results of the survival and choice experiments do not explain why tarnished plant bug was typically more abundant on hybrid vetches than on crimson clover. Early-instar tarnished plant bug nymphs may find the extrafloral nectar of the vetches more accessible than the floral nectar of crimson clover. Such an effect on early-instar nymphs could have led to the observed differences in densities. Subterranean clovers appear to provide both a less-attractive and less-favorable habitat for Lygus lineolaris (Palisot de Beauvois) than either crimson clover or the hybrid vetches. Preferred use of subterranean clovers in rotation or as interplants might reduce tarnished plant bug in agroecosystems.

In a replicated trial in North Carolina, House (1989) reported that corn was grown following no-till or conventionally-tilled winter cover crops of hairy vetch, crimson clover, or wheat. Hairy vetch harbored a more abundant and diverse below-ground arthropod fauna (herbivores and predators) than did crimson clover or wheat. Elateridae, Curculionidae, and Carabidae were particularly abundant following no-till hairy vetch. Scarabaeidae were especially abundant following conventionally-tilled clover. Elateridae (wireworms) were the dominant herbivores in no-till systems. Observed faunal differences had dissipated by July.

Crimson clover is more tolerant of Meloidogyne spp. than are red, white, or arrowleaf clovers (Quesenberry et al., 1986), but Duke (1981) listed 19 types of plant-parasitic nematodes that have been isolated from the roots. McKenry (pers. comm.) has stated that crimson clover is a good host for Meloidogyne hapla and other Meloidogyne spp.

Guertal et al. (1998) reported on replicated greenhouse pot and field studies in Alabama on the effects of winter-annual cover crops on southern root-knot nematode (Meloidogyne arenaria) and reniform nematode (Rotylenchulus reniformis), two plant-parasitic species. In the greenhouse pot trial using fine sandy loam soil, hairy vetch showed an increase of reniform nematode density (population index = 1.43 [final nematode density divided by initial nematode density]), common vetch (cv 'Cahaba White') maintained the existing reniform nematode densities (population index = 0.99), and reniform nematode densities were decreased both for cereal rye (population index = 0.37) and no cover crop (control) (population index = 0.08). Final reniform nematode densities for hairy vetch were not significantly different from those for common vetch; both of these, however, differed significantly for final densities for cereal rye and control. The latter two treatments did not differ from one another.

In a field study on fine sandy loam soil in southeastern Alabama, Guertal et al. (1998) reported that densities of southern root-knot nematode (Meloidogyne arenaria) on okra were significantly increased by preceding winter cover crops of common vetch, hairy vetch, or crimson clover, by comparison with plots lacking cover crops.

Guertal et al. (1998) concluded that the vetches tested are maintenance hosts for reniform nematode (Rotylenchulus reniformis) and should not be grown prior to susceptible cash crops, such as cotton. Cereal rye or bare fallow would be a better choices based on this criterion.

Crimson clover is more resistant to diseases than are most alternative clovers (Baltensperger et al., 1987), and it is said to tolerate viral diseases (Duke, 1981). However, July sowing of crimson clover can result in stand failure due to virus (Knight, 1985).

Crimson clover is said to be tolerant of weeds (Duke, 1981).

Weed above-ground biomass in a replicated study (r=4) at Blue Heron Vineyard, Hopland, Mendocino County, California on May 15-16, 1991, for cv 'Flame' was 0.607+/-0.153 Mg/ha (Mean +/- S.E.M.), which was 12.34% of the weed biomass attained in control plots. Dominant winter annual weeds were chickweed, shepherds purse, rattail fescue, and annual ryegrass. In early May, vegetational cover data by cv 'Flame' was 71.50+/-17.12 % (Mean +/- S.E.M.) (Bugg et al., unpublished data)

Purslane and water grass were difficult to control following no-till crimson clover in southern Georgia (relay intercropping with cantaloupe) (Bugg, 1990).