Subterranean clover (Duke, 1981) and subclover (Duke, 1981; Finch & Sharp, 1983) the common names.

There is dispute over the taxonomic status of subterranean clovers; some systematists have said that three species are comprised, and that subterranean and subclover are common names applied to three clover species: Trifolium subterraneum L. , T. yanninicum Katznelson and Morley and T. brachycalycinum Katznelson and Morley (Smith and Roquette, Jr., 1988). Others have written that there are three subspecies of Trifolium subterraneum L>, as noted: Trifolium subterraneum L. spp. subterraneum Katznelson and Morley, Trifolium subterraneum spp. yanninicum Katznelson and Morley. (Mackay and Barnard, 1981), and Trifolium subterraneum spp. yanninicum Katznelson and Morley (Mackay and Barnard, 1981), and Trifolium subterraneum spp. brachycalycinum Katznelson and Morley (Duke, 1981.). Trifolium subterraneum L. spp. subterraneum comprises the cultivars 'Enfield' (Mackay and Barnard, 1981), Green Range' (AHPRA, 1985), 'Junee' (AHPRA, 1985), 'Karridale' (AHPRA, 1985). Trifolium subterraneum spp. yanninicum includes 'Meteora' and 'Trikkala' (Mackay and Barnard, 1981). Trifolium subterraneum spp. brachycalycinum includes 'Clare' and 'Koala' (Hill et al., 1991; Graves, pers. comm.).

The subterranean clovers include numerous cultivars (Finch & Sharp, 1983) with varying flowering and maturation dates and low-temperature requirements for reproduction (McGuire, 1985). Cultivars also vary greatly as to soil pH and moisture optima and tolerances, heights, biomass production, proportion of hard seed, and concentrations of estrogenic compounds (R.L. Bugg, pers. comm.).

Many varieties of subterranean clover were produced in Australia (McLeod, 1982; McGuire, 1985). Collectively, strains are adapted over a wide range of rainfall zones and soils (McLeod, 1982).

In high rainfall areas of Victoria, Australia, Clark et al. (1991) found that 'Trikkale' and 'Larisa' (both spp. yanninicum) persisted over 8-12 years of sheep pasturing better than 'Yarloop' (spp. yanninicum) or 2 replications of spp. subterraneanum 'Mt. Barker' or 'Woogenellup.'

Graves et al. (1991) planted various subclover lines in the hills of San Diego and San Luis Obispo counties, then evaluated persistence over 7 years and production of the phytoestrogen formononetin. The hardseeded accessions 312-A, 92, 59, and 1142 showed significantly better persistence (P<0.05) than the Australian cultivars 'Geraldton', 'Nungarian' and 'Daliak' in San Diego County. In San Luis Obispo County, the 4 Spanish accessions mentioned above and accession 704 showed significantly better persistence in 1985 than did 'Nungarian' and 'Daliak'. During 1987, no significant differences were found in San Luis Obispo County.

Formononetin (which causes abortion in sheep) extractions showed that line 312-A had an unusually high concentration: 0.339% in Feb. 1987, 0.136% in March, 1987. 'Geraldton' also showed high concentration (0.161%) during Feb. 1987. Other accessions showed concentrations less than 0.06% at both sampling dates.

Subterranean clover has the advantage of producing inaccessible (below-ground) seed, which ensures regeneration of the stands (McGuire, 1985). Duke (1981) described the seed as large, broadly ellipsoid, and purplish black, with 143,325 seeds/kg. McGuire (1985) described the seed as black or purplish black, but white in the case of Trifolium yanninicum (e.g., 'Yarloop' [Murphy et al., 1976]).

'Meteora' seed is ovoid, cream to amber, and relatively large (Mackay and Barnard, 1981). 'Trikkala' has large cream seeds (Mackay and Barnard, 1981).

Subclover has an establishment advantage over the other clover species because of its large seed (Evers, 1988).

Hard seed will not germinate at planting but will at some later date (Evers, 1988); this is apparently a survival mechanism in areas with erratic weather. Relative hard seededness varies among subclover cultivars, as recounted by Mackay and Barnard (1981) hardseededness ratings, on an increasing scale from 1 to 10 were:

'Junee' hard-seededness is high for its maturity, approaching that of cv. 'Dinninup' (Mackay and Barnard, 1981).

'Karridale': Seeds are medium sized and black (AHPRA, 1985).

'Karridale' hardseededness is moderately low, similar to or slightly higher than that of cv 'Woogenellup' and higher than that of cv 'Mt. Barker' (AHPRA, 1985).

'Green Range' hard-seededness in Western Australia has been moderately high, equal to or a little higher than that of cvv. Seaton Park and Esperance and clearly higher than that of cv. Woogenellup. In New South Wales tests, hard-seededness has only been similar to that of cv. Woogenellup. Burr burial approximates that of cv. Woogenellup. (AHPRA, 1985.)

The subterranean clover varieties 'Nungarin', 'Seaton Park', and 'Woogenellup' were evaluated under various watering and defoliation regimes. Development of hard (impermeable) seed in 'Nungarin' and 'Seaton Park' was reduced by continuous watering. Repeated defoliation during flowering reduced seed yield in all three varieties tested. Defoliation prolonged flowering. On the other hand, defoliation before flowering is known to increase seed yield (Archer, 1990).

Seed of cv 'Seaton Park' exhibits embyo dormancy, which prevents germination despite permeable seedcoat and imbibition of water. This appears to have some value in protecting seed from microbial attack as well as out-of-season germination (Archer, 1990).

As noted by Murphy et al.(1976), numbers of seed per unit weight also vary among cultivars, as follows (in seeds/lb):

Other figures include:

• 'Green Range,' 130,000 seeds/kg (AHPRA, 1985);
• 'Junee', 150,000 per kg (Mackay and Barnard, 1981);
• 'Karridale,' 130,000 per kg (AHPRA, 1985);
• 'Meteora,' 100,000 per kg (Mackay and Barnard, 1981); and
• 'Trikkala,' 90,000 per kg (Mackay and Barnard, 1981).

Subterranean clover seed contains 30-40% protein (McGuire, 1985).

Subclover seedlings should have 3 to 8 nodules when they reach the three-leaf stage in presence of proper rhizobia and are more vigorous and have more leaves and nodules than crimson and arrowleaf clovers at 3 and 7 weeks after planting (Evers, 1988).

During establishment, the force produced by legume seedlings may be crucial in overcoming the weight of overlying soil and surface crusts. Williams (1956) used glass tubes containing vermiculite and glass rods of known mass to estimate the force produced by seeds of crimson clover, rose clover, subterranean clover, and alfalfa. 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.

As noted by McGuire (1985), taxonomic distinction of subclovers is clearest at flowering. Nonetheless, seedlings do exhibit some morphological differences; for example, 'Junee' seedlings are prostrate, relatively small and fine, with unifoliate leaf moderately hairy and with a small central crescent spot and narrow white arms curving down to the leaf lower margin (Mackay and Barnard, 1981). 'Karridale' seedlings are erect, with unifoliate leaf moderately hairy, with a small and inconstant crescent spot in the center (AHPRA. 1985). Machado et al. (1974) conducted a pot experiment that entailed shading with aluminum foil boxes the cotyledons (seed leaves) of 'Clare' subterranean clover seedlings 20 days after sowing. Seedlings that had shaded cotyledons weighed on the average 68.1 mg (dry phytomoass) whereas unshaded plants weighed 149.2 mg (P<0.05). This experiment highlighted the importance of photosynthesis by cotyledons in promoting vigorous seedling growth.

Duke (1981) described subterranean clover as a decumbent, large-seeded winter annual legume, more or less softly pubescent with stems slender, procumbent to decumbent, 0.5-4.0 (rarely to 8) dm long, forming circular clumps; leaves are all long-petioled; leaflets broadly obcordate, entire except for the shallowly crenate apex; stipules ovate to oblong-ovate, the lowermost acuminate, otherwise acute to obtuse; peduncles axillary, reflexing, elongating, and burying the heads in the soil after anthesis; inflorescence a few-flowered fascicle becoming a globose head in fruit; fertile flowers 2-5, whitish, striped with rose, 12-14 m long; sterile flowers developing after anthesis, numerous, apetalous, finally completely enclosing the pods; calyx of fertile flowers nerveless, the tube glabrous, the subequal flexous teeth ciliate, equalling the tube, at first setaceous, becoming stout; corolla about twice the length of the calyx; sterile flowers with calyx-teeth rather unequal, narrow, irregularly bent, slightly exserted, 1-seeded. McGuire (1985) mentioned that stems and runners of subterranean clover are prostrate and do not develop adventitious roots.

Smith and Roquette (1988) also stated that subclover has prostrate, non-rooting stems; the inconspicuous flowers are white or white with pink veins and arise from leaf axils. After self-fertilization, the flower stem (peduncle) bends toward the ground as a burr develops around the seed pods.

Subterranean clover is self-fertile and cleistogamous (McGuire, 1985).

Various cultivars have morphological and other characteristics, as recounted by various authors (Editor's note).

In cv 'Bacchus March' most burs are produced above ground (Murphy et al., 1976).

Mackay and Barnard (1981) wrote that cv 'Enfield' has hairy stems that are reddish brown when exposed to sunlight. The petioles are relatively short, hairy and reddish brown when exposed. The leaves are dark green and moderately hairy with more hairs on the lower surface than on the upper. The first leaves have a light green crescent and, if conditions are cold, the rest of the leaf, above and below the crescent, can be heavily pigmented with anthocyanin. As the plant develops to the rosette stage the color fades, leaving a few purple flecks and the light green, arrowhead-shaped crescent which usually does not extend to the edge of the leaflet. The stipules are highly pigmented, if exposed, but in a dense sward only the veins are red. The calyx tube is green but the lobes have some anthocyanin. The flowers are white with purple veins in the standard. In a sward, the flowers develop close to the ground and are therefore much less visible from above than in other varieties.

Murphy et al. (1976) described cv 'Geraldton' as having leaves sparse, long runners, and as being an abundant seed producer, and a winter producer.

According to (AHPRA, 1985), cv 'Green Range' has slightly indented leaflets together with prominent leaflet crescent markings inherited from it Nangeela grandparent. The crescent is angular and comprises a yellow-green central area, rising to a point close to the leaflet margin, with strong white arms on either side descending to the base of the leaflet. In winter or under some other conditions restricting growth, coarse purplish-red flecking is variably prominent, especially just above and below the crescent, together occasionally with purplish-brown pigmentation outlining the crescent or forming a partial bar along the midrib below the crescent. The stipules have strong, bright purplish-red pigmentation over much of their surface, especially towards the base of runners. Leaflet upper surfaces sparsely to moderately hairy. Petioles and stems sparsely to moderately hairy, peduncles moderately hairy; all with weak to moderate purplish-brown pigmentation where exposed to the sun. Calyx green apart from occasional light purplish-brown pigmentation of the teeth. Corolla is white with fine pink veins.

Mackay and Barnard (1981) described cv 'Junee' as having a broad- triangular, moderately indented leaflet and leaflet crescent marking similar to that of cv 'Tallarook', derived from that cultivar via cv 'Howard.' The crescent has only slight curvature and, in early leaves, consists of a small central light green area with variable and sometimes faint whitish arms at either side. Late in the growing season, often only the white arms are visible. In winter and under certain other conditions conducive to slow growth, there is usually some purple-red flecking in the vicinity of the leaflet midrib and occasional flecks elsewhere, together with brownish purple flushing mainly of the area below the crescent. Stipule and calyx light green. Corolla is white with pinkish red veins. Leaflet upper surfaces sparsely to moderately appressed-hairy. Petioles and stems sparsely hairy and peduncles more or less hairless. Stems relatively slender, with slight to moderate purplish brown pigmentation where exposed to the sun. In the reproductive phase, 'Junee' can be distinguished from cv. Howard, despite similar leaf and calyx markings, by the lesser hairiness of its leaves, petioles, stems, and especially peduncles, which are nearly glabrous as opposed to the densely hairy peduncles of 'Howard.'

According to AHPRA (1985), cv 'Karridale' has rounded leaflets and prominent, rounded leaflet crescent markings inherited from its 'Nangeela' grandparent. The crescent comprises a yellow-green central area with strong white arms on either side, curving towards the vase of the leaflet. In winter or under some other conditions restricting growth, coarse purplish red flecking is variably prominent, especially just above and below the crescent, together occasionally with purplish brown pigmentation outlining the crescent. Stipule veins purplish red, usually with a moderately prominent transverse bar of the same color. Leaflet upper surfaces more or less hairless. Petioles sparsely hairy, stems moderately hairy, peduncles moderately appressed-hairy: all robust, with moderate brownish purple pigmentation where exposed to the sun. Calyx green apart from occasional light purplish brown pigmentation of the teeth. Corolla white with fine pink veins.

Mackay and Barnard (1981) termed cv 'Meteora' a typical member of subspecies yanninicum and wrote that it was almost glabrous, possessing long petioles. Leaflets are large and bright green on long petioles. Leaflet markings are distinct from the other yanninicum cvv 'Yarloop' and 'Trikkala'. The leaflet crescent is conspicuous and yellow green, reaching the margin of the leaflet in mature leaves. There are no crescent arms or conspicuous leaf flecks. Stipules are green with red veins and a red flush between the veins under cool conditions. Calyx tube is green, glabrous, corolla white. Pods large, leathery and enclosed in the large transversely wrinkled calyx. In the burr, 2-3 pods protrude from the sparsely distributed sterile calyxs.

Mackay and Barnard (1981) described cv 'Trikkala' as a typical member of subspecies yanninicum, being almost glabrous with long petioles. Leaf, flower, and stipule characteristics as for cv. Larisa.

According to Duke (1981), subclover tolerates mean annual temperatures of 5.9-21.3 C, with a mean of 34 cases of 14.4 C. Subterranean clovers include a large number of varieties representing wide ranges of maturation dates and of low-temperature requirements for reproduction (McGuire, 1985). The species is well adapted to Mediterranean climate of cool, wet winters and hot, dry summers (Smith and Roquette, Jr., 1988). Cool, moist, mild winters are essential for persistence (Hofstetter, 1988). There are both warm and cold boundaries to subterranean clover production. Flowering by subclovers is induced by low temperatures (vernalization). Late-maturing cultivars are prevented from flowering by lack of cold; early-maturing cvv may be required in warm areas. By contrast, protracted cold weather can delay flowering and seed set (McGuire, 1985). Once established, seedlings can survive temperatures as low as 10 F (McLeod, 1982). In the Willamette Valley of Oregon, -14 degrees Centigrade accompanied by dry wind led to complete loss of pastures of 'Nageela', 'Mt. Barker', and 'Tallarook'. In other areas, subterranean clover stands (rosette stage, mid-season and late cultivars) have recovered after temperatures as low as -20 degrees Centigrade. 'Clare' stands were lost in Mississippi after a low temperature of -15 C; other strains survived (McGuire, 1985). Cv 'Yarloop' is subject to frost injury, according to Murphy et al. (1976).

Temperature effect on vegetative growth were studied at three diurnal temperature regimes. Subclover showed a linear increase in relative growth rate with temperature up to 15 to 25 C (Guerrero and Williams, 1975).

Duke (1981) stated that subterranean clover is assigned to the Mediterranean and Australian Centers of Diversity and ranges from the Cool Temperate Steppe top Wet through Subtropical Dry to Moist Forest Life Zones, and is adapted to areas with more than 400 mm of annual rainfall and below 1,000 m in elevation. Munz (1973) did not mention the species as naturalized in California, but it is widespread in hills of the North Coast counties, and is common in Mendocino County grazing lands (Bugg, pers. comm.).

Nearly all varieties of subterranean clover were first developed in Australia (McGuire, 1985).

Geographic suitabilities in California have been variously described. Graves et al. (1986) asserted suitability at elevations below 3500 feet, whereas Peaceful Valley (1988) stated that the species is suited for areas with 10 inches or more of rain, below 3000 ft., and McLeod (1982) stipulated 20 inches of annual rainfall and below 3,300 ft.

In western San Diego County below 3500' elevation, Murphy et al., (1976) suggested 'Geraldton,' 'Nungarin' and 'Northam.' With limited irrigation from September through June and at elevations below 4,000, 'Seaton Park,' 'Trikkala,' 'Enfield', and 'Meteora' are suitable.

Because of the varying tolerances of the three species of subterranean clover, soil conditions do not usually restrict production. Temperature and rainfall, however, do (McGuire, 1985). Duke (1981) reported that subterranean clover tolerates mean annual precipitation of 3.8-16.3 dm, with the mean of 34 cases bing 9.0 (35.42 inches). McGuire (1985) reported that high summer rainfall can prompt premature germination of sub clover seed and decrease its persistence.

Subterranean clover has been said to require 10 inches or more of rain (Murphy et al., 1976; Peaceful Valley, 1988), 12 inches of irrigation or rainfall (Munoz & Graves, 1988), and 20 inches of annual rainfall (McLeod, 1982).

Minimum rainfall requirements (in inches) were given by Murphy et al. (1976). Seasonal distribution is important as well as total rainfall. In general, later-maturing cultivars rquire more and later rain than do early varieties. Minimum rainfall values indicate that the clover should be expected to reseed in an area of the state with the long-term annual rainfall indicated:

'Tallarook' needs late spring rains to ensure seed maturation (Murphy et al., 1976).

'Enfield' grows well in a range of environments from 450 mm annual rainfall to 900 mm annual rainfall (Mackay and Barnard, 1981).

Cv 'Junee' is adapted to areas where cvv 'Woogenellup' and 'Esperance' are grown, where it may be more persistent than 'Woogenellup' and possibly 'Green Range,' especially where summer rainfall is heavy and rainfall variability is high, or where cropping is relatively frequent. Because of its large proportion of hard seed, it may be able to extend into some areas of shorter or less reliable growing season where cv 'Seaton Park' is now grown (Mackay and Barnard, 1981).

'Karridale' has tolerated high-rainfall areas of southern mainland Australia, giving good winter and very good spring production. It has been seen as a direct replacement for cv 'Mt. Barker,' and perhaps 'Woogenellup' in the wet part of that cultivar's range (AHPRA, 1985).

Cv 'Meteora' tolerates waterlogging; its growth in flooded conditions is 93% of unflooded controls and similar to cv 'Yarloop' (Mackay and Barnard, 1981), which also tolerates high soil water (Murphy et al., 1976).

The subterranean clover varieties 'Nungarin,' 'Seaton Park,' and 'Woogenellup' were evaluated under various watering and defoliation regimes. Development of hard (impermeable) seed in 'Nungarin' and 'Seaton Park' was reduced by continuous watering. Repeated defoliation during flowering reduced seed yield in all three varieties tested. Defoliation prolonged flowering. On the other hand, defoliation before flowering is known to increase seed yield (Archer, 1990).

Seed of cv 'Seaton Park' exhibits embryo dormancy, which prevents germination despite permeable seedcoat and imbibition of water. This appears to have some value in protecting seed from microbial attack as well as out-of-season germination (Archer, 1990).

Earlier maturing, shorter-statured subclover causes less moisture depletion for associated warm-season grass than later maturing, taller clovers (e.g., 'Yuchi' arrowleaf, 'Bigbee' berseem) (Bade et al., 1988).

A combination of P and K can increase subclover production (Haby, 1988). McGuire (1985) wrote that superphosphate has been the most important fertilizer used on rangeland to support subterranean clover and that sulfur and molybdenum can also be limiting. McLeod (1982) emphasized the importance of phosphate fertilization. Peaceful Valley's (1988) account said that subterranean clovers thrive with low soil fertility, but growth and nitrogen fixation are greater on soils supplemented with phosphorus, calcium, and sulfur.

Haby (1988) wrote that 40 or more lbs S/acre increased yields 45 % over treatments receiving only phosphorus. Clover growing on deeper sandy soils should be more responsive to S applications. Micronutrient requirements in acid soils are thought to include molybdenum, boron, and in heavily limed soils, possibly zinc. Copper increased subclover yields in Australia.

In a growth chamber study by Guerrero and Williams (1975), Filaree (Erodium botrys) and subterranean clover (Trifolium subterraneum cv 'Woogenellup') were grown in sole and mixed cultures in a phosphorus-deficient range soil (from Butte County) and in sand with differing levels of supplemental nitrogen, phosphorus, and sulfur. Filaree dominated if phosphorus was limiting, whereas subterranean clover did so if nitrogen were left out of the fertilizer. Subterranean clover has a higher requirement for phosphorus than does filaree and also appears less capable of exploiting insoluble phosphatic sources. Addition of superphosphate to rangeland soils is suggested as a means of promoting subterranean clover.

Shock et al. (1984) added the equivalent of 0, 10, and 80 kg of S per ha were added to lysimeters containing monocultures and bicultures, of subterranean clover, soft chess, and filaree. The equivalent of 100 kg of N per ha was also added as ammonium chloride. Addition of sulfur improved uptake of fertilizer nitrogen by subterranean clover and soft chess monocultures and in subterranean clover + soft chess and subterranean clover + filaree bicultures. Addition of sulfur fertilizer increased the percentage of N derived from fixation by subterranean clover.

As recounted by Barrow and Mendoza (1990), sigmoid yield responses to increasing levels of a nutrient (e.g., P) suggest that there is a lower threshold concentration below which plants cannot take up the nutrient, and diminishing returns to further addition of the nutrient above an upper threshold. Those scientists conducted trials with freshly-applied vs. incubated phosphate using a yellowish brown loamy sand (pH 5.6), and found markedly sigmoid response curves for subterranean clover (cv 'Yarloop') and narrow-leafed lupin (Lupinus angustifolius), but not for L. cosentinii or L. luteus. The results suggest that the lupins (especially L. cosentinii) grew better than subterranean clover at low phosphorus concentration. At low levels of phosphate application, roots of subterranean clover were heavily infected with vesicular-arbuscular mycorrhizae; infection but no arbuscules were detected with the lupins. Previous studies had suggested that responses of subterranean clover to added phosphorus are not sigmoid in the presence of mycorrhizal fungi. Findings of the present study were contrary to this.

Based on pot experiments and literature review, burr medic and barrel medic are not as efficient at absorbing P as is subterranean clover. Yellow serradella is more efficient at absorbing P from soil than either subterranean clover or burr medic (Paynter, 1990).

Iron deficiency is often most pronounced on soils with high pH. On sites with calcareous soils and high pH, 'Mt. Barker' and 'Woogenellup' have shown iron deficiency symptoms (chlorosis). By contrast 'Koala' and 'Clare' have shown no chlorosis, and 'Larisa' and 'Trikkala' showed only slight chlorosis (Gildersleeve et al., 1988).

In Californian rangeland dynamics, high soil nitrogen leads to dominance by nonlegumes, whereas legumes dominate when phosphorus and sulfur are elevated (Shock et al., 1984). Evers (1988) confirmed that grass and weeds can retard subclover stands if high rates of nitrogen are used. When nitrogen fertilizer was applied to a subclover-ryegrass mixture there was no decrease in nodulation at up to 50 lbs/acre. Subclover alone showed decreased nodulation at the lowest rate (25 lbs/acre).

Apply P (and K if required) fertilizer in the fall just before expected clover germination. Avoid N fertilizer in the fall when attempting to establish or re-establish clover (Ocumpaugh, 1988).

Clover forage production averaged 37% less when 100 lbs N/acre were applied to bermuda grass and bahiagrass the previous summer. Subclover growth, reseeding, and persistence are improved if nitrogen fertilizer is not applied the previous summer (Evers and Smith, 1988).

Hochman et al. (1990) reported that, based on detailed replicated field trials in New South Wales, Australia, decline of subterranean clover on acid soils was related to root rot caused by the fungal pathogen Phytophthora clandestina and by low P availability. Liming did not reduce disease incidence, and on one site led to decreased P availability, where soil pH was elevated above 5.5.

According to Duke (1981), subterranean clover tolerates soil pH of 4.5-8.2, with the mean of 31 cases being 6.1. Haby (1988) maintained that subterranean clovers do not tolerate pH 5.1, and soils which have a pH below 5.5 should be limed to 6.0 or above. In general, the species is best adapted to acid or moderately acid to neutral soils (Murphy et al., 1976; Finch & Sharp, 1983; Graves et al., 1986; Munoz & Graves, 1988; Peaceful Valley, 1988; Miller et al., 1989). T. subterraneum, including the cultivars 'Mt. Barker,' 'Woogenellup,' and 'Tallarook,' are well adapted to and highly productive on sandy, acid soils, where the newer varieties 'Esperance', 'Larisa', and 'Meteora' also show promise. T. brachycalycinum, including cvv 'Clare' and 'Koala', predominates on neutral and more alkaline soils (Smith and Roquette, Jr., 1988). Indeed, those two cvv are the most productive cultivars of subterranean clover where soil pH exceeds 7.2 (Bade et al., 1988; Evers, 1988; Reed et al., 1989), with 'Mt. Barker' and 'Karridale' faring well at lower pH (Bade et al., 1988). Most varieties of subterranean clover can stand moderately acid soil (McGuire, 1985).

Subterranean clover varieties 'Koala,' 'Meteora,' and 'Clare' yielded the most on a calcareous site, and 'Trikkala,' 'Larisa,' and 'Koala' yielded particularly well on an acid site. In general, 'Koala' has performed particularly well on alkaline soils (Gildersleeve et al., 1988).

As recounted by Richardson et al. (1988), nodulation of subterranean clover is reduced at solutions of pH lower than 5.0, and eliminated below 4.5. Low numbers of rhizobia were present. Nodulation is also sensitive to Al concentrations of 10 micromoles or greater. These restrictions can be somewhat reduced by the addition of Ca and P. To ensure proper nodulation of subterranean clover throughout the rooting profile, lime should be incorporated, rather than merely placed on the soil surface. Plants compensate for low pH by nodulating more in the less-acidic portions of the soil profile. Inoculation and calcium coating of seeds did not alleviate poor nodulation in the acidic zones.

Evans et al. (1988) found that nodulation of 'Woogenellup' subterranean clover is reduced when soil pH is below a threshold level of about 5.0. Liming improves this situation. Although rhizobia may ultimately attain the same densities in acid as in limed soils, their accumulation is not as rapid in the former during autumn and winter.

Gildersleeve et al. (1988) wrote that iron deficiency is often most pronounced on soils with high pH. On sites with calcareous soils and high pH, susceptible species exhibit symptoms of iron deficiency chlorosis when grown on high pH, high base status soils containing free calcium carbonate. 'Clare' and 'Koala' are the only Australian varieties available suggested for calcareous soils. Both performed well in field and greenhouse trails in Texas. 'Mt. Barker' and 'Woogenellup' have shown iron deficiency symptoms (chlorosis). By contrast 'Koala' and 'Clare' have shown no chlorosis, and 'Larisa' and 'Trikkala' showed only slight chlorosis.

When paired with either 'Seaton Park' or 'Daliak' subterranean clovers in a 3-year field replacement-series study, the cultivar 'Clare' (Trifolium brachycalycinum) dominated the mixed stands. Soil pH was 5.4-5.5; mowing was once every 4 weeks. Petiolar length of 'Clare' is much greater than the early-maturing 'Daliak,' and slightly greater than the mid-season maturing 'Seaton Park.' Under stress, 'Clare' also showed better seedling vigor and survival and greater seed production per plant. Dry matter production by 'Clare' also is less dependent on plant density. There was evidence of overyielding by mixtures of 'Clare' and 'Seaton Park.' 'Clare' seed reserves appeared to be more greatly reduced over the summer months than were those of 'Seaton Park' or 'Daliak.'

Because cultivars of the three species of subterranean clover vary in their tolerances, soil conditions do not usually restrict production as temperature and rainfall do (McGuire, 1985). Duke (1981) wrote that subterranean clover does especially well on light soils, although it tolerates heavy soils, and that the species grows well and reseeds on all well-drained soils that can sustain white clover. Munoz & Graves (1988) wrote that the species tolerates loam to clay soils. McLeod (1982) stated that growth is best in well drained, loam soils and that the species does well on hilly land. However, varieties of T. yanninicum (e.g., 'Meteora', 'Trikkala', and 'Yarloop') do well on waterlogged soils (McGuire, 1985), on which this species is widely distributed (Smith and Roquette, Jr., 1988).

Bade et al. (1988) mentioned that subterranean clover performs very well on clay pan soils so long as pH is below 7.3. Sub clover is adapted to most of the fine sandy loam and clay upland soils in Southeast Texas.

Serpentine soils are widespread in the California Coast Range and Sierra Nevada, where many winegrape vineyards are located. In a greenhouse pot study, Jones et al. (1977) assessed biomass production by 'Mt. Barker' subterranean clover in soils of the Henneke series (a lithic argixeroll). Soils from 23 sites subjected to 7 fertilizer regimes (including unfertilized control) with 4 replications of each combination. Biomass production by subterranean clvoer showed that if P and S were supplied, addition of Ca increased yield on 17 sites, K on 10, and Mo on 14.

Subterranean clover shows moderate shade tolerance (Brinton, 1989).

Early- or mid-season-maturing cultivars of subterranean clover may be needed where orchard shade is dense. On the other hand, based on observations in Contra Costa County apple orchards, moderate shade may improve growth and reproduction of later-maturing varieties by reducing evapotranspiration and resultant water stress (Bugg, 1990). In dense shade of a mature walnut orchard Russell Lester's (Solano Co.), subterranean clovers, remained green until June 17, when 'Lana' vetch had already turned brown due to lack of irrigation (Bugg, pers. comm., 1993).

Fifteen cultivars of subterranean clover and one of balansa clover were grown in conjunction with perennial ryegrass and evaluated for tolerance to four herbicides applied separately and in some two-way combinations: 2,4-DB, MCPA-Na salt, MCPA amine, and bromoxynil, 2,4-DB + bromoxynil, MCPA-Na salt + bromoxynil, MCPA amine + bromoxynil. The subterranean clovers evaluated were 'Clare,' 'Nuba,' 'Larisa,' 'Meteora,' 'Trikkala,' 'Dalkeith,' 'Enfield,' 'Esperance,' 'Green Range,' 'Junee,' 'Karridale,' 'Mt. Barker,' 'Nungarin,' 'Seaton Park,' and 'Woogenellup.' The sole representative of Trifolium balansae was cv 'Paradana.' Based on visual assessment, 2,4-DB was the most damaging herbicide and bromoxynil the least. 'Trikkala' (Trifolium subterraneum ssp. yanninicum) showed particularly good tolerance of herbicides. Within the subspecies brachycalycinum, 'Clare' showed much better tolerance than did 'Nuba' (Evans et al., 1989).

Griffin and Dabney (1990) reported that subterranean clover was controlled by paraquat at 1.1 kg ai/ha (80% control when applied in early April; 100% control in early May). Glyphosate and SC-0224 applied in April gave 53% control. HOE-39866 applied in April gave excellent control of subterranean clover.

Subterranean clover is tolerant of Paraquat, 2,4-DB, and Poast (Lanini, pers. comm.) and is more resistant to glyphosate than most other cover crops (Bugg, pers. comm.).

Ocumpaugh (1988) recommended avoiding both herbicides toxic to clover and "brush control" herbicides such as picloram, unless these can be applied as a spot treatment or with a carpet roller. Such herbicides have enough residual effect to prevent clover establishment for a year or more. Subclover will tolerate low rates of 2,4-D, but weeds will not be controlled unless the herbicide is applied when the weeds are small.

On neutral and alkaline soils, competition by burclover and its rhizobia can interfere with establishing subterranean clover stands. Burclover is very sensitive to 2,4-D herbicide and can be removed with an application of 0.75 lb/a (Bade et al., 1988).

Duke (1981) and McGuire (1985) both term subterranean clover a winter annual. The species is self-fertile and cleistogamous (McGuire, 1985), and the flowers do not attract insect visitors (Bugg, pers. comm.). Cocks (1990) reported that for various medics, up to 95% of fully-opened flowers abort, failing to produce mature pods. By contrast, for subterranean clover, the range is from 23-63%. Abortion may be a means of ensuring that seed are sufficiently large to produce viable seedlings.

After flowering, peduncles reflex and drive the seed heads underground (Duke, 1981). As remarked by McGuire (1985), this provides the advantage of inaccessible (below-ground) seed, which ensures regeneration of the stands.

The subterranean clover varieties 'Nungarin', 'Seaton Park', and 'Woogenellup' were evaluated under various watering and defoliation regimes. Development of hard (impermeable) seed in 'Nungarin' and 'Seaton Park' was reduced by continuous watering. Repeated defoliation during flowering reduced seed yield in all three varieties tested. Defoliation prolonged flowering. On the other hand, defoliation before flowering is known to increase seed yield (Archer, 1990).

Seed of cv 'Seaton Park' exhibits embyo dormancy, which prevents germination despite permeable seedcoat and imbibition of water. This appears to have some value in protecting seed from microbial attack as well as out-of-season germination (Archer, 1990).

From Nedlands, Western Australia, Cotterill (1990) reported that subterranean clover (cv 'Seaton Park') produced less dry matter biomass early (by the equivalent of December 15 here) but had produced more by the equivalent of March 7 here than 'Serena' burr medic. A mixture of the grasses Bromus diandrus, Hordeum leporinum, Lolium rigidum, and Vulpia myuros reduced growth by both legumes.

Seeding rates have been variously recommended as 9-13 kg/ha or 20 kg/ha aerial seeding (McGuire, 1985), 10-20 lb/acre (Hofstetter, 1988), 12 lb/acre (Finch & Sharp, 1983), 12-20 lbs/acre of raw seed (Graves et al., 1986), 15 lb/acre (Miller, 1988), 15-30 lb/acre (Munoz & Graves, 1988), 22-28 kg/ha (broadcast) (Duke, 1981), 20 to 30 lbs/acre (McLeod, 1982; Miller et al., 1989), and 20-30 lb per acre (Peaceful Valley, 1988).

Evers (1988) suggested a general seeding rate of 10 to 16 lbs/acre. Increasing the seeding rate increases the amount of early forage production and a solid cover is formed earlier. The seeding rate needed for a satisfactory subclover stand increases as the seedbed becomes rougher and/or the weed and grass competition becomes more severe.

Subterranean clover can be sown in prepared seed beds at a depth of about 1 cm; it can also be seeded aerially (McGuire, 1985).

Evers (1988) suggested that the best stands occur when seeds are placed in the top on-half inch of soil. If planting in a well drained sandy soil, drilling the seed in narrow rows about 3/4-inch deep may be more desirable. 1/4 to 1/2 inches was recommended by Peaceful Valley (1988), and 1/2 inch by McLeod (1982).

Subterranean clover can be sown in prepared seed beds at a depth of about 1 cm; it can also be seeded aerially (McGuire, 1985).

If feasible, plant seed into the soil as opposed to surface sowing in order to extend the survival of the rhizobia bacteria (Weaver, 1988).

Evers (1988) reported that broadcasting the seeds resulted in the highest yields. Drilling in narrow rows gave better yields that did drilling in wide rows. Broadcasting the seed delayed competition between clover seedlings for light and moisture and produced a solid canopy of subclover quicker. Drilling the seed in rows resulted in early competition between clover seedlings within the row and delayed forming a solid canopy within until the plants were big enough to cover the area between the rows.

Seedbed should be smooth, firm, and free of clods. Covering the seeds with soil protects inoculant on the seed, and improves water retention. Rolling is recommended, especially on clay or loam soils (Evers, 1988).

The small grain seed box on a regular grain drill will work for subclover if high seeding rates (about 15 lbs/acre or higher) are used. Lower rates can be used if the clover is mixed with ryegrass (Evers, 1988).

Subterranean clover should be seeded in mixes at heavier (than medics) rates (8 to 15 lbs/acre) in the early fall before the first rains (Miller et al., 1989).

Subterranean clover should be seeded onto a firm seedbed in the fall (Finch & Sharp, 1983).

Recommended planting dates are in the early fall (Lanini, pers. comm.; Munoz & Graves, 1988); or simply in the fall (McLeod, 1982; Finch & Sharp, 1983; Miller, 1988; Peaceful Valley, 1988).

According to Evers (1988), good germination of subclover does not occur until the daily low temperature reaches the mid-60's. An early planting date maximizes fall forage production before winter but also increases the risk of losing the clover stand to fall drought. Delaying the planting date for cooler temperatures increase the amount of time for germination and seedling establishment and reduces the amount of fall forage production. However, there is less risk of drought.

The WR rhizobial strain (Nitragin Co.) (the same strain as for rose clover) is appropriate for subterranean clover (Burton and Martinez, 1980; Duke, 1981; Munoz & Graves, 1988).

Information on rhizobial requirements is limited. Nodulation and growth on a new site with strains WU95 and CC2480a was good. TA1 was slightly inferior (Mackay and Barnard, 1981).

In field tests rhizobial strains differed in ability to compete with ineffective native rhizobia and in ability to survive the long summer drought. In composites, poor or moderately effective rhizobial strains reduced the effectiveness of the good strains. Subclover growth increased in field experiments as the amount of inoculum was increased, indicating that high rhizobial numbers were important. Peat inoculum applied with 40% gum arabic solution as a sticker and a lime coating was much superior to peat inoculum applied as a water slurry. Vacuum-inoculation treatment gave no better results than uninoculated seed. The effectiveness of inoculation sticker materials fell generally in the following decreasing order: "PELGEL-PELINOC", gum arabic-lime, methyl-cellulose-lime, sugar lime (Jones et al., 1978).

Cultivars of subclover differed in responses to strains of rhizobia. 'Woogenellup' was more specific than was 'Mt. Barker' (Jones et al., 1978).

Jones et al. (1978) reported trials with subterranean clover indicating that that effective rhizobia could be impeded by ineffective native rhizobia. To be effective, rhizobia must be able to survive the long summer drought. Therefore, 2-year studies that include reseeding stands are needed. Cultivar 'Woogonellup' performed best when inoculated with rhizobial strain X-47 and was more specific in rhizobial affinity than was 'Mt. Barker'. In 2nd-year stands, 'Woogonellup' did best with strain X16; 'Mt. Barker performed adequately with strains X16 and X20. Peat-based inoculum was superior to other forms. Effectiveness of glues in descending order was "PelGel-Pellinoc" > gum arabic-lime > methylcellulose-lime > sugar-lime.

Evans et al. (1988) stated that nodulation of 'Woogenellup' subterranean clover is reduced when soil pH is below a threshold level of about 5.0. Liming improves this situation. Although rhizobia may ultimately attain the same densities in acid as in limed soils, their accumulation is not as rapid in the former during autumn and winter.

Bade et al. (1988) wrote that on neutral and alkaline soils, competition by burclover and its rhizobia can interfere with establishing subterranean clover stands. Burclover is very sensitive to 2,4-D herbicide and can be removed with an application of 0.75 lb/a.

'Mt. Barker' has been the most available variety (Bade et al., 1988), and some cultivars are hard to find, with new cultivars replacing old ones (Slayback, pers. comm.). Most of the subclover seed is produced in Australia, but there is a small amount of seed of 'Mt. Barker' produced in Oregon; it is best to order seed at least one month before the desired planting date (Evers, 1988).

Most major agricultural seed retailers in California sell subterranean clover; readily available cultivars include 'Dalkeith', 'Koala', 'Mt. Barker', 'Seaton Park', and 'Trikkala' (Bugg, pers. comm.).

Variation among stains in the number of days to flowering may be as much as 60 days (Murphy et al., 1976). Smith and Roquette, Jr. (1988) indicated that days to flowering vary among cultivars as follows: 'Nungarin' - 77, 'Northam' -'78, 'Dwalganup' - 83, 'Geraldton' - 97, 'Daliak' - 97, 'Dalkeith' - 98, 'Uniwager'- 103, 'Yarloop' - 109, 'Seaton Park' - 110, 'Trikkala' - 112, 'Dinninup' - 113, 'Enfield' - 118, 'Esperance' - 120, 'Junee' - 128, 'Green Range' - 128, 'Clare - 129, 'Woogenellup' - 130, 'Howard' - 93-135, 'Bacchus Marsh' - 131, 'Karridale' - 136, 'Mt. Barker' - 137, 'Larisa' - 142, 'Nangeela' - 143, 'Meteora' - 148, and 'Tallarook' - 163.

Starting times for flowering periods were related by Murphy et al. (1976) as follows: early-season (late Jan. - early Feb.) cultivars are 'Geraldton', 'Dwalganup', 'Daliak;' early-midseason (mid-Feb.- March) are 'Seaton Park', 'Yarloop', 'Dinninup;' mid-season (March and April) are 'Woogenellup', 'Howard', 'Clare', 'Bacchus March', 'Mt. Barker', 'Nangella;' and late-season (late April and May) is 'Tallarook'.

Cv 'Green Range' flowers and matures in early mid season, about the same time as cv 'Woogenellup' (approximately 128 days at Perth with early May sowing), and 6-9 days earlier than cv 'Karridale' (AHPRA, 1985).

'June' flowers in early midseason, about a week earlier than cv. 'Woogenellup' in inland and southern Western Australia. At Perth it flowers about the same time as 'Woogenellup' (about 128 days with early May sowing, which would correspond to early November sowing in the northern hemisphere) (Mackay and Barnard, 1981).

'Karridale' shows mid-season flowering, about the same time as cv. 'Mt. Barker' and 6-9 days after cvv. 'Green Range' and 'Woogenellup.' At Perth (Australia), flowering occurs about 136 days after early May sowing (AHPRA, 1985).

Cv 'Trikkala' typically flowers slightly later than cv 'Yarloop' or about 118 days after germination in Western Australia (Mackay and Barnard, 1981).

Cv 'Koala' has been termed a midseason-flowering variety (Fred Thomas, pers. comm.).

In general, subterranean clover matures during May (Finch & Sharp, 1983), but there are large number of varieties representing a wide range of maturation dates (McGuire, 1985). Cultivars are grouped according to the length of time required to reach maturity or seed set, as early, early mid-season, mid-season, and late-season (Murphy et al., 1976). The earliest and latest strains may differ by as much as 60 days (McLeod, 1982).

McLeod (1982) listed the following as early maturing: 'Geraldton,' 'Dwalganup,' 'Daliak.' Mid-season-maturing cultivars are 'Dinninup,' 'Woogenellup,' and 'Mt. Baker,' with 'Tallarook' listed as late maturing and requiring five months to mature. 'Yarloop' was stated to require ample water, and 'Clare' to tolerate high pH.

Early-maturing, relatively-hardseeded Australian varieties include 'Nungarin,' 'Northam,' 'Dalkeith' (Miller et al., 1989).

According to Miller et al. (1989), early- to mid-early-season maturing varieties include 'Nungarin,' 'Northam,' 'Geraldton,' 'Daliak,' 'Dalkeith'. Early-mid-season to mid-season varieties include 'Seaton Peak,' 'Trikkala,' 'Enfield,' and 'Esperance'. Mid-season varieties include 'Clare,' 'Woogenellup,' 'Howard,' and 'Mt. Barker'. Late mid-season cultivars include 'Larisa,' 'Nangella,' and 'Meteora.' Late varieties include 'Tallarook.'

McLeod (1982) listed 'Geraldton,' 'Dwalganup,' and 'Daliak' as early varieties, 'Dinninup,' 'Woogenellup,' and 'Mt. Baker' as mid-season cultivars, and 'Tallarook' as late.

Low rainfall, high evaporation, shallow soils with southern exposure, or high elevations can lead to short growing seasons, favoring early strains like 'Geraldton,' 'Dwalganup,' or 'Daliak.' Where growing seasons are longer, mid- season strains like 'Dinninup,' 'Woogenellup,' or 'Mt. Barker,' would be suitable. The late strain 'Tallarook' requires at least a five months (Murphy et al., 1976).

Early-maturing varieties like 'Geraldton,' 'Northam,' and 'Nungarin' are recommended for areas with short growing season (e.g., San Diego County) (Graves et al., 1986). 'Enfield' matures a little earlier than 'Woogenellup' (Mackay and Barnard, 1981), whereas 'Green Range' matures in early mid season, about the same time as cv 'Woogenellup' (AHPRA, 1985). 'Junee' maturation is a week or more earlier than 'Woogenellup,' or about the same as cv 'Esperance' (Mackay and Barnard, 1981). 'Karridale' matures in mid-season, about the same time as cv 'Mt. Barker' and 6-9 days after cvv 'Green Range' and 'Woogenellup' (AHPRA, 1985). 'Meteora' shows late mid-season maturity (7-10 days later than cv 'Mt. Barker') (Mackay and Barnard, 1981). 'Trikkala' matures early; the trait is derived from a simply inherited Neuchatel gene which may produce earlier than normal flowering with a very early seasonal break (Mackay and Barnard, 1981).

Subterranean clover will self-seed readily (Miller, 1988; Munoz & Graves, 1988). Subterranean clover does best at reseeding when the canopy is opened up by grazing (or presumably mowing). Defoliation actually increases seed production (McGuire, 1985). However, per McLeod's account (1982), grazing should be curtailed at flowering to allow reproduction.

Seed matures in the burr at or below the soil surface which allows seed production under moderately intensive grazing (Smith and Roquette, Jr., 1988). Evers and Smith (1988) confirmed that subclover can produce seed under close grazing, unlike most other annual clovers. Moderate grazing to a 2- to 3-inch height increases seed production. In Oregon studies, seed production is greatest when subclover is grazed until early burr formation. Moisture stress during flowering and seed maturation reduced yields. Subterranean clover can produce in excess of 500 lbs of seed/acre in Oregon and produce from 200 to 400 lbs/acre in Texas.

Duke (1981) described seed harvest as entailing close mowing with a lespedeza cutter bar. The residue is then windrowed. Pea lifter guards attached above the bar are useful when the clover growth is especially heavy. Alternatively, the clover can be mowed closely but above the seed heads with a standard mower. Then a strong hay rake can be used to pull up and windrow the runners and heads. Clover plants must be completely dry for this to be successful; remaining seed heads can be collected by vacuum. Threshing can be done using stationary or combine threshers.

According to McGuire (1985), in Australia, burrs were long harvested using rakes, sweepers, and sheepskin rollers. More recently, Australians have harvested using suction combines, after the soil surface is disturbed enough to allow the buried seed to be picked up and separated from the earth. Seed yields can be as high as 2 Mg/ha, but 500-1,000 kg/ha is more typical.

For various medics, up to 95% of fully-opened flowers abort, failing to produce mature pods. By contrast, for subterranean clover, the range is from 23-63%. Abortion may be a means of ensuring that seed are sufficiently large to produce viable seedlings (Cocks, 1990).

Cv 'Enfield' produced more burrs per unit area and more seeds per burr than 'Woogenellup.' Seeds are small, and their density can be almost twice that of 'Woogenellup.' Most of the seed is formed above ground, as with 'Woogenellup' and 'Trikkala' (Mackay and Barnard, 1981).

'Esperance' shows high seed yields, and in studies conducted in Denmark with mild clover scorch infections in all treatments, 'Esperence' yields greatly exceeded those of 'Woogenellup' and 'Seaton Park' (Mackay and Barnard, 1981).

'Geraldton' is an abundant seed producer (Murphy et al., 1976).

When rainfall is high (850 mm or greater), 'Meteora' seed yields have been satisfactory (400 kg/ha. or greater), but this late variety produces an unusually high proportion of residual hard seeds (60% or more), and this may lead to low plant density in second-year stands if summers are cool (Mackay and Barnard, 1981).

In general, seed has intermediate longevity (McLeod, 1982), with hardseeded cultivars showing extended viability (Peaceful Valley, 1988).

Duke (1981) described the species as a more or less softly pubescent annual legume, with stems slender and procumbent to decumbent. Miller et al. (1989) and Finch & Sharp (1983) termed it a prostrate plant that buries its seed pod after flowering. Mackay and Barnard, (1981) described it as semi-prostrate.

It has also been called indeterminate (Bugg et al., 1989), but indeterminacy is better expressed in later-maturing cultivars.

Different cultivars show differing habits and statures. 'Enfield' is prostrate (Mackay and Barnard, 1981). 'Green Range': is moderately robust (AHPRA, 1985). 'Junee' is prostrate in the early stages, but it changes to semi-erect after flowering (Mackay and Barnard, 1981). 'Karridale' grows vigorously, appearing semi-prostrate early but becoming erect after flowering (AHPRA, 1985). 'Meteora' shows an erect, tall growth habit (Mackay and Barnard, 1981).

Subterrranean clover may grow to a height of 6 to 8 inches. (Graves et al., 1986; Finch & Sharp, 1983).

In southern Georgia, a study indicated that subterranean clover varieties attained maximum heights as noted (cm, Mean+/-SEM, where cultivar was replicated): 'Enfield': 23.63; 'Esperance': 15.00; 'Howard': 22.75; 'Junee': 18.25; 'Nangeela': 21.75; Talarook': 15.50; "Mississippi Ecotype": 16.00; 'Koala': 34.63+/-1.63; 'Larisa': 24.88+/-0.63; 'Meteora': 23.63+/-0.88; 'Trikkala': 29.75+/-1.25; 'Mt. Barker': 23.88+/-1.25 (Bugg, pers. comm.).

In a replicated study (r=4) at the Blue Heron Vineyard (Fetzer Vineyards), Hopland, Mendocino County, California, May 2, 1991, heights for the various subterranean clovers were as follows (cm, Mean +/-S.E.M.): 'Koala': 45.72+/-2.93, 'Dalkeith': 31.75+/-1.27, 'Trikkala': 43.82+/-1.60, 'Mt. Barker': 36.83+/-2.64, and 'Seaton Park': 37.47+/-2.40 (Bugg et al., unpublished data).

Subterranean clover has a taproot with many fibrous supporting roots; the stems and runners of subterranean clover are prostrate and do not develop adventitious roots (McGuire, 1985). According to Fred Thomas (pers. comm.), early taproot development by subterranean clover is not as rapid as that of burclover. Therefore, in mixed stands, burclover is favored by a germinating rain in early autumn followed by a drought, whereas continuous moisture from autumn on favors subterranean clover.

Subterranean clover tolerates close grazing, has large seeds that make establishment easier and enable early fall production, and is weed suppressive (Bade et al., 1988). Nonetheless, Finch & Sharp (1983) noted that weed control is usually required in the establishment phase, because young subterranean clover plants are poor competitors. Mow competing weeds to a height of 2-4 inches during establishment .

Ocumpaugh (1988) wrote that while managing mixed stands, these should be grazed short (or, presumably in orchards or vineyards, mowed) by the time subterranean clover seedlings are germinating. Continuous grazing can begin after subclover seedlings have 4 to 6 trifoliate leaves. Continue grazing until cool temperatures limit grass growth. If reseeding is desired, do not overgraze during April and early May (in Texas) when seed is developing, especially if rainfall is below normal.

As reported by Williams (1956), 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.

Tillage can be timed to determine floristic composition of swards, as noted by Forcella and Gill (1986). Seeds of subterranean clover and annual ryegrass (Lolium rigidum) are less persistent than sorrel (Rumex acetosella) and common knotweed (Polygonum aviculare). Red brome (Bromus rubens), silvergrass (Vulpia spp.), and subterranean clover dominated only where tillage was in summer or early autumn. Annual ryegrass was most abundant where soil was tilled in late autumn and early winter. Sorrel and common knotweed were favored only by winter tillage.

Abdul-Baki and Teasdale (1993) described a production system for fresh market tomatoes in Maryland, involving mulches produced by mowing either hairy vetch or subterranean clover, or of horto paper or black polyethylene plastic on preformed beds. A high-speed flail mower was used to convert the two winter-annual, September-sown cover crops to mulch. Tomato seedlings were transplanted on May 1 or 8. Black polyethylene plastic mulch led to the best early production but overall yield was best with hairy vetch. Subclover was less winter-hardy than hairy vetch.

Subterranean clover has the advantage of of inaccessible (below-ground) seed, which ensures regeneration of the stands (McGuire, 1985). Subterranean clover is susceptible to shading by associated grasses, and benefits from removal of most plant residues before autumn (McGuire, 1985). To maintain subclover stands, mow periodically during winter and early spring (Graves et al., 1986). McGuire (1985) wrote that subterranean clover reseeds best when the canopy is opened up by grazing (or presumably mowing). Defoliation actually increases seed production.

Ocumpaugh (1988) wrote that while managing mixed stands, these should be grazed short (or, presumably in orchards or vineyards, mowed) by the time subterranean clover seedlings are germinating. Continuous grazing can begin after subclover seedlings have 4 to 6 trifoliate leaves. Continue grazing until cool temperatures limit grass growth. If reseeding is desired, do not overgraze during April and early May (in Texas) when seed is developing, especially if rainfall is below normal.

Dabney et al. (1989) found that no-till management resulted in better reestablishment of subterranean clover stands than did spring tillage.

Bugg et al. (unpublished data) found that under no-till management in an organic vineyard in Hopland, Mendocino County, California, subclovers were seeded in replicated plots in October 1990 and evaluated for reestablishment in the spring of 1992. Cvv 'Koala,' 'Mt. Barker,' and 'Trikkala.'showed good re-establishment in the second year, but 'Dalkeith' and 'Seaton Park' did not. This may have been related to the hardseededness and embryo dormancy discussed by Archer (1990).

Forcella and Gill (1986) reported that tillage can be timed to determine floristic composition of swards. Seeds of subterranean clover and annual ryegrass (Lolium rigidum) are less persistent than sorrel (Rumex acetosella) and common knotweed (Polygonum aviculare). Red brome (Bromus rubens), silvergrass (Vulpia spp.), and subterranean clover dominated only where tillage was in summer or early autumn. Annual ryegrass was most abundant where soil was tilled in late autumn and early winter. Sorrel and common knotweed were favored only by winter tillage.

Graves et al. (1987) conducted a 6-year study in southern and central Californian grasslands under medium to heavy grazing. These scientists found that several Spanish subterranean clovers with hardseededness showed better persistence and vegetational coverage than did the more commonly-available Australian varieties 'Geraldton', 'Nungarin', and 'Daliak'. Particularly promising were the Spanish strains 312-A, 92, 59, and 1142. All the Spanish strains flowered later than 'Nungarin', which is of concern because early maturation helps ensure reproduction in years with no late rains. Strain 312-A showed the latest flowering, 6 weeks after 'Nungarin', but also the best persistence.

In a follow-up study, Graves et al. (1991) reported that hardseeded Spanish subterranean clovers show as good or better persistence on southern and central Californian foothills and coastal areas than does the most persistent Australian cultivar, 'Geraldton', and show lower concentrations of estrogenic compounds.

Archer (1990) evaluated the subterranean clover varieties 'Nungarin', 'Seaton Park', and 'Woogenellup' under various watering and defoliation regimes. Development of hard (impermeable) seed in 'Nungarin' and 'Seaton Park' was reduced by continuous watering. Repeated defoliation during flowering reduced seed yield in all three varieties tested. Defoliation prolonged flowering. On the other hand, defoliation before flowering is known to increase seed yield. Seed of cv 'Seaton Park' exhibits embyo dormancy, which prevents germination despite permeable seedcoat and imbibition of water. This appears to have some value in protecting seed from microbial attack as well as out-of-season germination.

Richardson et al. (1988) maintained that to ensure proper nodulation of subterranean clover throughout the rooting profile, lime should be incorporated, rather than merely placed on the soil surface. Plants compensate for low pH by nodulating more in the less-acidic portions of the soil profile. Inoculation and calcium coating of seeds did not alleviate poor nodulation in the acidic zones. Nodulation of subterranean clover is reduced at solutions of pH lower than 5.0, and eliminated below 4.5. Low numbers of rhizobia were present. Nodulation is also sensitive to Al concentrations of 10 micromoles or greater. These restrictions can be somewhat reduced by the addition of Ca and P.

Hill et al. (1991) found that when paired with either 'Seaton Park' or 'Daliak' subterranean clovers in a 3-year field replacement-series study, the cultivar 'Clare' (Trifolium brachycalycinum) dominated the mixed stands. Soil pH was 5.4-5.5; mowing was once every 4 weeks. Petiolar length of 'Clare' is much greater than the early-maturing 'Daliak,' and slightly greater than the mid-season maturing 'Seaton Park.' 'Clare' also showed better seedling vigor and survival and greater seed production per plant under stress. Dry matter production by 'Clare' is less dependent on plant density. There was evidence of overyielding by mixtures of 'Clare' and 'Seaton Park.' 'Clare' seed reserves appear to be more greatly reduced over the summer months than were those of 'Seaton Park' or 'Daliak.' Cultivars of Trifolium brachycalycinum (e.g., 'Clare') supposedly suited mainly to neutral to alkaline soils and is believed less tolerant to close grazing and less able to bury its burrs than is T. subterraneum (e.g., 'Seaton Park,' 'Daliak').

Subterranean clover is susceptible to shading by associated grasses, and it benefits from removal of most plant residues before autumn (McGuire, 1985). Subclover can produce seed even under continuous grazing (Bade et al., 1988). Several authors emphasized subclover's tolerance of mowing or grazing, and recommended mowing at 2-4 inch or 3-4 inch height during establishment and periodically thereafter, in order to reduce weeds (Finch & Sharp, 1983; Evers and Smith, 1988; Graves et al., 1986; Munoz & Graves, 1988; Peaceful Valley, 1988; Miller et al., 1989). Miller et al. (1989) prescribed frequent mowing at 2-4 inches height to allow subclover to compete with weeds and to have a good seed set.

Evers and Smith (1988) noted that the low growth of subclover enables it to tolerate mowing. If associated weeds show upright growth, mowing to 3- to 4- inch height will favor subclover. Spring mowing after winter weeds begin flowering but before seeds are produced will reduce weed densities the next year.

McGuire (1985) wrote that subterranean clover reseeds best when the canopy is opened up by grazing (or presumably mowing). Defoliation actually increases seed production.

Ocumpaugh (1988) wrote that while managing mixed stands, these should be grazed short (or, presumably in orchards or vineyards, mowed) by the time subterranean clover seedlings are germinating. Continuous grazing can begin after subclover seedlings have 4 to 6 trifoliate leaves. Continue grazing until cool temperatures limit grass growth. If reseeding is desired, do not overgraze during April and early May (in Texas) when seed is developing, especially if rainfall is below normal.

Archer (1990) evaluated the subterranean clover varieties 'Nungarin,' 'Seaton Park,' and 'Woogenellup' under various watering and defoliation regimes. Repeated defoliation during flowering reduced seed yield in all three varieties tested. Defoliation prolonged flowering. By contrast, defoliation before flowering is known to increase seed yield.

Motazedian and Sharrow (1986) varied mowing height and frequency in mixed stands of subterranean clover and perennial ryegrass. In stands dominated by perennial ryegrass, greater stubble heights led to greater productivity; the opposite was true for stands dominated by subterranean clover. The greatest interval between defoliations (49 days) led to the greatest productivity of the stands.

Phillips et al. (1983) concluded that subterranean clover (cv 'Woogenellup') is apparently compatible in mixture with soft chess ('Blando' brome), at least with periodic mowing.

Christensen (1971) proposed that in Californian vineyards, French plowing would leave a narrow strip of cover crops in each alley and would permit use of early-maturing species like brome grass, bur clover, 'Geraldton' subterranean clover, and the rose clovers. Mowing cover crops could reduce the threat of frost. Dates for plowing down cover crops depends on the maturation dates early to mid-June for subterranean clovers.

No-till management resulted in better reestablishment of subterranean clover stands than did spring tillage (Dabney et al., 1989)

Forcella and Gill (1986) reported that tillage can be timed to determine floristic composition of swards. Seeds of subterranean clover and annual ryegrass (Lolium rigidum) are less persistent than sorrel (Rumex acetosella) and common knotweed (Polygonum aviculare). Red brome (Bromus rubens), silvergrass (Vulpia spp.), and subterranean clover dominated only where tillage was in summer or early autumn. Annual ryegrass was most abundant where soil was tilled in late autumn and early winter. Sorrel and common knotweed were favored only by winter tillage.

Duke (1981) reported that subterranean clover seed can be harvested when the plants are dead and thoroughly dry. Harvest by mowing close to the ground with a tractor-drawn power take-off lespedeza cutter bar, and windrowing. For especially dense stands, it is important to have pea lifter guards that attach over the upper surface of the bars. Alternatively, if the plants are thoroughly dry, mow with a standard mower, then use a strong hay rake to pull up the runners and burs, and windrow. Remaining heads can be vacuumed up.

McGuire (1985) reported that seed harvesting in Australia typically involves suction combines, after the soil surface is disturbed enough to allow the buried seed to be picked up and separated from the earth. Seed yields can be as high as 2 Mg/ha, but 500-1,000 kg/ha is more typical.

Subterranean clovers may be mowed by flail or rotary mowers (Bugg, pers. comm.).

Subterranean clovers collectively have the greatest use of any annual clovers (McGuire, 1985).

Advantages to subterranean clover include its tolerance of close grazing, its ease of establishment and early fall production due to large seed size, and its suppression of weeds (Bade et al., 1988). Duke (1981) noted that subterranean clover is useful for pasture when grown with companion grasses, and that it is also suitable for silage or hay; its decumbent habit and mat of creeping stems make it suitable for erosion control. Miller et al. (1989) wrote that subterranean clover is the most productive legume for use in orchards and vineyards below 4,000 feet. Finch & Sharp (1983) recommended its use in orchards and vineyards below 3,000 feet. Peaceful Valley (1988) cited it as useful for dryland and drip irrigated orchards, including uncultivated almonds, and vineyards, and described it as excellent for range land reseeding and hilly land. Other applications include intercropping with grains on acidic soils (Peaceful Valley, 1988) and green manure (McLeod, 1982).

Glatzle (1989) described ley-farming systems (cereal grain production alternating with pasture) with annual, self-regenerating legumes as being increasingly used in areas with Mediterranean climate. In particular, practices in southern and southwestern Australia involve the use of self-regenerating stands of annual medics (Medicago polymorpha, M. truncatula, M. littoralis, M tornata, M scutellata, and M. rugosa) and subterranean clovers (Trifolium subterraneum L., ssp. subterraneum, brachycalycinum, and yanninicum). Advantages include production of high-quality forage, need to sow pasture but once, increased yield of cereal in response to nitrogen added by pasture legumes, soil protection and improvement, and stabilization of farmers' incomes.

Subterraneum clover is used in grass mixtures, particularly warm- season perennial grasses like bermudagrass, kleingrass, bahiagrass, and dallisgrass. Grasses are most productive when clover is not present. During the period when both are growing, the pasture must be managed to favor the clover. Subclover matures about the time that summer grasses initiate active growth (Ocumpaugh, 1988).

Wick and Alleweldt (1983) found that when grown together in containers, subterranean clover cv 'Clare' caused a 20% reduction in growth by Riesling grape vines. The mechanism for this inhibition was not known, and it occurred regardless of the level of nitrogen fertilization. No such inhibitory effect was seen for subterranean clover cv 'Daliak' or for white clover. The legumes supplied nitrogen to the vines when only low amounts of nitrogen were added, and there was higher use of water by vines with legumes.

When grown outside in a young vineyard in Germany, 'Daliak' showed more rapid early growth than white clover, but was damaged by frost and did not reseed (Wick and Alleweldt, 1983).

Stirzaker et al. (1992) grew tomatoes in Camden, New South Wales, Australia, using various production systems, including winter cover cropping with 'Nungarin' and 'Woogenellup' subterranean clovers, used to promote an in situ-grown mulch.

Stirzaker et al. (1992) in Sydney, New South Wales, Australia, experimented with variuos lettuce/tomato production systems, including cultivated lettuce/tomato, zero-tillage lettuce/tomato, subclover/lettuce/tomato, and fallow/lettuce/tomato. Subclover led to reduced erosion by comparison with all other treatments. Soils under subclover had greater bulk density and greater water content and lower air porosity than soils from the cultivated treatment. Tomato yields were significantly greater with subclover than with fallow or cultivation in the first crop. Tomato yields did not differ significantly among treatments in the second crop. Soil organic matter in the 0-30 mm stratum was significantly greater under subclover/lettuce/tomato than any other treatment, 30 months after the start of the rotation. The subclover mulch production method was never adopted by farmers in Australia, and has been abandoned by Stirzaker and colleagues because of its complexities (Stirzaker, pers. comm.).

Stasiak (1990) found that peach seedlings transplanted into established vigorously growing subterranean clover stands showed reduced growth the first year, but increased growth by the second year.

Murphy et al. (1976) recounted that mixtures of several varieties are usually more productive than any single variety alone. Recommendations (lbs/acre) depend on local conditions and seed availability.

 

Zone 1: North Coast (rainfall 35" or more):

• 'Geraldton' and/or 'Daliak' subclover - 2 lbs/acre
• 'Woogenellup' and/or 'Howard' subclover - 2 lbs/acre
• 'Mt. Barker' subclover - 3 lbs/acre 'Tallarook' subclover - 2 lbs/acre

Zones 1 and 2: North and Central Coast, coastal valley (rainfall 20-35"):

• 'Geraldton' and /or 'Daliak' subclover - 2 lbs./acre
• 'Woogenellup' and /or 'Howard' subclover - 2 lbs/acre
• 'Dinninup' and/or 'Seaton Park' subclover - 2 lbs/acre
• 'Mt. Barker' subclover - 2 lbs/acre
• 'Wilton' rose clover - 1 lbs/acre

Zones 2, 4, and 5: Central Coast and higher foothills (rainfall 15-35"):

• 'Geraldton' and /or 'Daliak' subclover - 2lbs./acre
• 'Woogenellup' and /or 'Howard' subclover - 2 lbs/acre
• 'Dinninup' and/or 'Seaton Park' subclover - 1 lbs/acre
• 'Mt. Barker' subclover - 1 lbs/acre
• 'Jemalong' and/or 'Harbinger' barrel medic - 2 lbs/acre
• 'Hykon' and/or 'Kondinin' rose clover - 1 lbs/acre
• 'Wilton' rose clover - 1 lbs/acre

Zone 3: South Coast (rainfall 10-20"):

• 'Geraldton' and/or 'Daliak' subclover - 2 lbs/acre
• 'Hykon' and/or 'Olympus' rose clover - 2 lbs/acre
• 'Jemalong' and/or 'Harbinger' barrel medic - 2 lbs/acre

Zones 4, 5, and 5A: Central Valleys (rainfall 10-20"):

• 'Wilton' rose clover - 2 lbs/acre
• 'Hykon' and/or 'Kondinin' rose clover - 2 lbs/acre
• 'Dinninup' and/or 'Seaton Park' subclover - 2 lbs/acre
• 'Geraldton' and/or 'Daliak' subclover - 2 lbs/acre
• 'Woogenellup' and/or 'Howard' subclover - 2 lbs/acre

Murphy et al.(1976) mentioned several replacement options. Cv 'Clare' can replace part of other midseason varieties ('Woogenellup', 'Howard', 'Seaton Park', or 'Dinninup') on heavy soils with pH of 7.5-9.0. 'Yarloop' subclover can replace midseason varieties on waterlogged soils. Crimson clover can be substituted for part of the rose clover, especially in grainland rotation.

Hill et al. (1991) found that when paired with either 'Seaton Park' or 'Daliak' subterranean clovers in a 3-year field replacement-series study, cv 'Clare' (Trifolium brachycalycinum) dominated the mixed stands. Soil pH was 5.4-5.5, mowing was once every 4 weeks. Petiolar length of 'Clare' is much greater than the early-maturing 'Daliak,' and slightly greater than the mid-season maturing 'Seaton Park.' 'Clare' also showed better seedling vigor and survival and greater seed production per plant, under stress. Dry matter production by 'Clare' also is less dependent on plant density. There was evidence of overyielding by mixtures of 'Clare' and 'Seaton Park.' 'Clare' seed reserves appear to be more greatly reduced over the summer months than were those of 'Seaton Park' or 'Daliak.' Trifolium brachycalycinum cultivars such as 'Clare' are supposedly suited mainly to neutral to alkaline soils, and are believed less tolerant to close grazing and less able to bury their burrs than is T. subterraneum.

Williams (1963) sowed Crimson clover (Trifolium incarnatum L., strain S. Australian commercial), rose clover (T. hirtum All., strain S.6), and subterranean clover (T. subterraneum L. cv 'Bacchus') in pure plantings and in 1:1 mixtures of two species. 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). Williams (1963) found that 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 (cirmson clover + subterranean clover) was no more productive than 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 is susceptible to shading by associated grasses, and benefits from removal of most plant residues before autumn (McGuire, 1985).

Williams et al. (1968) stated that subterranean clover has, on the average, larger seed than does crimson clover, and plot studies 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.

Bade et al. (1988) reported that on neutral and alkaline soils, competition by burclover and its rhizobia can interfere with establishing subterranean clover stands. Burclover is very sensitive to 2,4-D herbicide, and can be removed with an application of 0.75 lb/a.

McGuire (1985) wrote that when a mixture of white clover and subterranean clover is sown, white clover completely dominates the moist sites, and subterranean clover dominates the dry sites.

Subterranean clovers can also be grown with grasses. In California, McGowan and Williams (1971) found that a cereal companion crop (barley) can increase the forage produced in the first year of sowing while permitting good growth and seed production of subterranean clover. This was determined on nine sites in the Sacramento Valley and adjacent foothills. Where grain yields were 2,000 kg/ha or less and soil moisture was adequate in April (the last month of the rainy season), undersown clover produced 3000 to 5000 kg/ha of seed, over 100 seeds per plant, and grain yields were not reduced by the undersowing. Subterranean clover (cv 'Woogenellup') is apparently compatible in mixture with soft chess ('Blando' brome), at least with periodic mowing (Phillips et al., 1983). Subterranean clover is sown along with perennial ryegrass on Oregon rangelands (McGuire, 1985). Shock et al. (1984) found that association with nonlegumes soft chess (Bromus mollis L.) or filaree (Erodium spp.) increased the percentage of N derived from fixation by subterranean clover.

Forcella and Gill (1986) found that tillage can be timed to determine floristic composition of swards. Seeds of subterranean clover and annual ryegrass (Lolium rigidum) are less persistent than sorrel (Rumex acetosella) and common knotweed (Polygonum aviculare). Red brome (Bromus rubens), silvergrass (Vulpia spp.), and subterranean clover dominated only where tillage was in summer or early autumn. Annual ryegrass was most abundant where soil was tilled in late autumn and early winter. Sorrel and common knotweed were favored only by winter tillage.

Evers (1988) reported that benefits of subclover are maximized when it is grown with a warm season perennial grass such as bermudagrass, bahiagrass, or dallisgrass. Planting in established sod is less expensive than on a prepared seedbed. However, stand establishment is more difficult due to competition. Avoiding the use of nitrogen fertilizer in late summer and in the late fall during establishment has improved stand and quantity of subclover. Subclover drilled into a bermudagrass sod produced 49% more forage than when the seed was broadcast. Success with broadcast seed on a grass sod is improved if planting is delayed until November when temperatures are cooler.

In combination with 'Coastal' bermudagrass (a warm-season grass) in Texas, annual dry matter biomass yields (kg/ha) for 'Mt. Barker' subterranean clover were as follows: 3,681; 2,430; and 1,636 kg/ha. In combination with common Bermuda grass (a warm-season grass) in Texas, annual dry matter biomass yields (kg/ha) for a mixture of subterranean clovers were as follows: 407; 937; and 1,349 kg/ha (Bade et al., 1988).

Christensen (1971) proposed using winter cover crops in Californian vineyards, with the aim of producing a sod-like condition. Cover crops would be low growing, require little or no mowing, and be self re-seeding. Their functions would be to reduce tillage and dust, provide habitat for predators that attack spider mites, improve water penetration, and provide nitrogen. Annual grasses suggested include barley, 'Blando' brome, or rye. Subterranean clovers recommended include cv 'Geraldton', Dwalganup', 'Howard', and 'Mt. Barker'. Rose clovers included cv 'Kondinin' and 'Hykon'. Medics suggested were California bur clover, 'Cyprus' barrel medic, and 'Harbinger' barrel medic. Mixtures of subterranean clovers were suggested so that better adapted varieties will reseed.

McGowan and Williams (1973) in Yolo County, California, in a replicated field study, grew subterranean clover (cv 'Woogenellup') in conjunction with barley (cv 'CM67'). Subterranean clover was established November 10-11 at an initial density of 100 clover plants per square meter (equivalent to a seeding rate of 10 kg/ha) in combination with barley sown and thinned to various densities (100 (control), 33 50, 200, or 400 plants per square meter) or with several alternative techniques to delay barley germination or emergence: (1) soaking with CCC (2-chloroethyl trimethylammonium); (2) seed coating with paraffin; (3) deep (10 cm) sowing; or (4) seeding of barley delayed by one or three weeks. In the final treatment, barley was clipped to a height of 2 cm 12 weeks after sowing. At the highest seeding density, barley reduced light transmission by 49%. This light reduction apparently was the principal cause for reduced subterranean clover biomass production and number of seeds per plant.

Subterranean clovers do not produce much biomass, according to Graves et al. (1986) and (Finch & Sharp, 1983).

Mean dry wt. of subclover in a three-year field trial in Georgia was 4.00 Mg/ha (Hargrove, 1986).

Dry matter yields (Mg/ha) obtained in individual studies of subterranean clover were given as: 3.8, 6.0, 4.0 (Smith et al., 1987).

In southern Georgia, a study during 1988-89 indicated that subterranean clover varieties drilled into prepared seedbeds attained the following estimated above-ground dry-weight phytomass values (Mg/ha, mean +/- SEM where replicated): 'Meteora': 5.9+/-0.6; 'Larisa': 6.9+/-2.3; 'Mt. Barker': 11.0+/-1.5; 'Esperance': 4.5; 'Nangeela': 5.6; 'Trikkala': 12.0+/-0.4; 'Junee': 5.0; 'Enfield': 5.2; 'Howard': 9.5; 'Koala': 10.6+/-.1; 'Talarook':7.4; Mississippi Ecoytpe 6.4 (Bugg, pers. comm.).

In prepared seedbeds in Texas, annual biomass yields (dry matter, kg/ha) for subterranean clovers were as follows: 'Mt. Barker': 1,205; 2,969; 3,393; 'Clare': 326; 2,856; 4,118; 'Meteora': 1,497; 2,894; 4,262; 'Karridale': 3,384; 3,280; 'Woogenellup': 2,113; 2,993; 3,567; and 'Koala': 3,799; 4,604 (Bade et al., 1988).

In a replicated trial in an organic vineyard in, Hopland, Mendocino County, California, Bugg et al. (1996) found that dry above-ground biomass measurements were as follows (Mg/ha, Mean +/- S.E.M.): 'Koala': 9.7+/-1.6; 'Dalkeith': 5.1+/-1.8; 'Trikkala': 8.3+/-1.4; 'Mt. Barker': 7.6+/-0.9; 'Seaton Park': 6.8+/-0.4 Mg/ha. When cover crops and weeds were included, the corresponding figures were: 'Koala': 9.8+/-1.6; 'Dalkeith': 7.4+/-1.9; 'Trikkala': 9.9+/-1.4; 'Mt. Barker': 8.2+/-0.9; and 'Seaton Park': 7.8+/-0.5.

Subterranean clover on rangelands in Oregon yields 5,000 to 6,000 kg/ha of dry matter (McGuire, 1985).

In combination with 'Coastal bermudagrass (a warm-season grass) in Texas, annual dry matter biomass yields (kg/ha) for 'Mt. Barker' subterranean clover were as follows: 3,681; 2,430; and 1,636 kg/ha. In combination with common Bermuda grass (a warm-season grass) in Texas, annual dry matter biomass yields (kg/ha) for a mixture of subterranean clovers were as follows: 407; 937; and 1,349 kg/ha (Bade et al., 1988).

Generalizations on N content of subclover are as follows: up to 100 or more lbs/acre/year (Haby, 1988), 50-200 lb of N per acre (Munoz & Graves, 1988); 207 kg/ha (FAO, 1984); and 114 kg/ha mean N content of three year field trial in Georgia (Hargrove, 1986). In unirrigated pasture, subterranean clover adds about 45 lb/a of nitrogen (Holland et al., 1969). A review article by Smith et al. (1987) reported an aboveground nitrogen content (kg/ha) of 114, proportion of nitrogen estimated obtained from fixation as 0.67, and the estimated N fertilizer equvalence under no-tillage regimes were given (kg/ha) as 12-103 (when followed by sorghum).

Subterranean clover (Trifolium subterraneum L., cv 'Woogenellup') was used as a cover crop preceding rice (Oryza sativa L., cv 'Labelle') under 2 clover regimes (clover vs. fallow), 2 tillage regimes (rototilling vs. no tillage), and 4 levels of nitrogen fertilizer addition (as urea): 0, 56, 112, and 168 kg/ha. Under the no-tillage regime, clover was suppressed by herbicide. The subterranean clover contained from 70-110 kg N/ha prior to rice planting, and increased rice yields by about 10% across both tillage and all nitrogen regimes (Dabney et al., 1989).

Subterranean clover did not reduce the amount of nitrogen required to generate maximum rice yields (Dabney et al., 1989).

In southern Georgia, a study during 1988-89 indicated that in monocultural plots, subterranean clover varieties attained estimated above-ground nitrogen contents as follows (kg/ha): 'Meteora': 129.656 +/-6.886; 'Larisa': 147.132+/-55.387; 'Mt. Barker': 251.335+/-10.357; 'Esperance': 82.206; 'Nangeela': 121.021; 'Trikkala': 224.024+/-9.691; 'Junee': 102.681; 'Enfield': 132.110; 'Howard': 201.891; 'Koala': 202.439+/-14.125; 'Talarook': 168.409; Mississippi Ecotype: 166.266 (Bugg, pers. comm.).

Association with nonlegumes soft chess (Bromus mollis L.) or filaree (Erodium spp.) increased the percentage of N derived from fixation by subterranean clover (Shock et al., 1984).

Soil nitrogen and organic matter levels showed significant improvement after five years of subclover covercropping at Ramona, San Diego County (Miller et al., 1989).

Kirchmann and Marstorp (1991) of Sweden provided foliar chemical analysis for some cover crops used in California, all at 101 days of age.

Thus, Persian clover contained 2.2% N, berseem 2.52% N, and subterranean clover 3.02% N.

In Sweden, Marstorp and Kirchmann (1991) reported the following values for stems and leaves of several legumes harvested from the field 100 days after emergence. and later used as green manure:

Nutrient contents of various subterranean clover cultivars were measured by Phatak, Bugg, and Brunson (unpublished data). In this replicated study, concentrations of various nutrients (mg/kg of dry phytomass) were compared using ANOVA. The following P-values were obtained for the relevant F-tests: boron, P= 0.0577; calcium, P=0.8399; potassium, P=0.1240; phosphorus, P=0.4856; magnesium, P=0.0250; sulfur, P=0.7267.

Descriptive statistics follow for the various cultivars: B mg/kg of dry phytomass (mean +/- Std. Error, if cultivar was replicated):

• METEORA: 18.829+/-1.446
• LARISA: 19.697+/-0.941
• MT.BARKER: 18.050+/-0.659
• ESPERANCE: 21.616
• NANGEELA: 18.775
• TRIKKALA: 14.226+/-0.059
• JUNEE: 20.376
• ENFIELD: 19.532
• HOWARD: 17.144
• KOALA: 21.128+/-0.484
• TALAROOK: 19.414
• MISSISSIPPI ECOTYPE: 17.889

Ca mg/kg of dry phytomass (mean +/- Std. Error, if cultivar was replicated):

• METEORA: 13692.106+/-610.984
• LARISA: 13575.356+/-1172.163
• MT.BARKER: 12881.711+/-927.680
• ESPERANCE: 11206.545
• NANGELLA: 12115.147
• TRIKKALA: 11809.496+/-3303.319
• JUNEE:13311.754
• ENFIELD: 16490.416
• HOWARD: 11650.270
• KOALA: 15078.899+/-507.172
• TALAROOK: 12643.182
• MISSISSIPPI ECOTYPE: 13247.438

K mg/kg of dry phytomass (mean +/- Std. Error, if cultivar was replicated).

• METEORA: 27995.577+/-4157.482
• LARISA: 32620.613+/-2940.122
• MT.BARKER: 27057.925+/-119.602
• ESPERANCE: 30306.330
• NANGELLA: 32046.234
• TRIKKALA: 20543.665+/-797.155
• JUNEE: 28391.463
• ENFIELD: 23615.138
• HOWARD: 25982.513
• KOALA: 34060.299+/- 1102.888
• TALAROOK: 34701.710
• MISSISSIPPI ECOTYPE: 35665.968

P mg/kg of dry phytomass (mean +/- Std. Error, if cultivar was replicated):

• METEORA: 2813.222+/- 294.019
• LARISA: 2863.098+/-247.964
• MT.BARKER: 2336.863+/-32.429
• ESPERANCE: 3090.885
• NANGELLA: 2935.841
• TRIKKALA: 1986.614+/-386.559
• JUNEE: 2577.234
• ENFIELD: 2602.051
• HOWARD: 2467.196
• KOALA: 2356.067+/-181.574
• TALAROOK: 2377.780
• MISSISSIPPI ECOTYPE: 2486.460

Mg mg/kg of dry phytomass (mean +/- Std. Error, if cultivar was replicated).

• METEORA: 2718.835+/-29.765
• LARISA: 2613.120+/-176.260
• MT.BARKER: 2467.165+/-47.175
• ESPERANCE: 2384.710
• NANGELLA: 2553.620
• TRIKKALA: 2180.280+/-76.220
• JUNEE: 2201.740
• ENFIELD: 2532.350
• HOWARD: 1966.270
• KOALA: 2750.290+/-48.990
• TALAROOK: 1976.130
• MISSISSIPPI ECOTYPE: 2031.180+/-0.000

S mg/kg (mean +/- Std. Error, if cultivar was replicated).

• METEORA: 55.780+/-7.590
• LARISA: 58.385+/-1.405
• MT.BARKER: 52.165+/-1.435
• ESPERANCE: 56.930
• NANGELLA: 50.700
• TRIKKALA: 54.505+/-9.255
• JUNEE: 55.270
• ENFIELD: 61.560
• HOWARD: 47.540
• KOALA: 66.900+/-0.050
• TALAROOK: 56.770
• MISSISSIPPI ECOTYPE: 51.130.

Subterranean clover can deplete soil moisture if not grazed heavily during a dry spring (Bade et al., 1988).

McGowan and Williams (1973) found that subterranean clover depleted soil moisture more than barley did. On March 27th, 19 weeks after sowing, maximal soil moisture was observed when barley was sown at the highest density and grown alone (ca 7.5% at 5-15 cm soil depth, ca 9.9% at 15-30 cm), i.e., without subterranean clover. Lowest soil moisture levels were obtained when subterranean clover was grown alone (ca 6.2% in the 5-15 cm soil stratum, and ca 8% in the 15-30 cm stratum). Presence of barley in mixes with subterranean clover did not accelerate soil moisture depletion over that observed with subterranean clover alone.

McGowan and Williams (1973) found that subterranean clover depleted soil moisture more than barley did. On March 27th, 19 weeks after sowing, maximal soil moisture was observed when barley was sown at the highest density and grown alone (ca 7.5% at 5-15 cm soil depth, ca 9.9% at 15-30 cm), i.e., without subterranean clover. Lowest soil moisture levels were obtained when subterranean clover was grown alone (ca 6.2% in the 5-15 cm soil stratum, and ca 8% in the 15-30 cm stratum). Presence of barley in mixes with subterranean clover did not accelerate soil moisture depletion over that observed with subterranean clover alone.

Kretschmar and Ladd (1993) in south Australia conducted a replicated laboratory trial on the release of 14C from decomposing leaves of subterranean clover as affected by: 1) three levels of earthworm densities (none, four per soil column, or seven per soil column of southern worm [Aporrectodea trapezoides]); 2) three possible soil compaction levels (200, 400, or 600 kPa); and 3) three levels of placement of 14C-labelled subterranean clover leaves (soil surface; mixed at depths of 39, 42, or 46 mm; and mixed in soil at ca 180-260 mm depth.) Data on CO2 evolution were collected over a period of 104 days. Earthworm presence and density markedly increased CO2 evolulation where soil was compacted and subterranean clover was incorporated deeply. In the absence of earthworms, deep incorporation with high compaction led to reduced CO2 evolution, and evidence of anaerobic decomposition : methane accumulation at depth.

As related by Murphy et al. (1976), subclover cultivars vary in their concentrations of pigments that can have estrogenic effects on animals. In nearly pure stands in Australia, estrogen levels of some subclover varieties have reduced lambing percentages. This has not occurred in California because (1) subclover usually is not over 50 or 60 per cent of the stand even in the best pastures, and (2) subclover varieties high in estrogen ('Yarloop,' 'Dinninup,' 'Tallarook') have not been widely used or have usually been mixed with low-estrogen varieties. Ratings for the cultivars follow:

• 'Bacchus March': Low;
• 'Clare': Low;
• 'Daliak': Low;
• 'Dinninup': High;
• 'Dwalganup': High;
• 'Geraldton': High;
• 'Howard': High;
• 'Mt. Barker': Low;
• 'Nangeela': Low;
• 'Seaton Park': Low;
• 'Tallarook': High;
• 'Yarloop': High;
• 'Woogenellup': Low.

'Trikkala' contains only low concentrations (0.07-0.15%, dry weight) of plant oestrogen formononetin (Mackay and Barnard, 1981).

In Werribee, Victoria, Australia, 'Enfield' contained 0.06 to 0.16 % of dry weight of formononetin, or about the same as 'Bacchus Marsh.' However, in Shenton Park, West Australia, from 1977 to 1981, 'Enfield' averaged 0.18 percent formononetin (range 0.07 to 0.31), whereas 'Bachus Marsh' averaged 0.03 percent (range 0.01 to 0.06) (Mackay and Barnard, 1981).

Formononetin content of cv 'Green Range' is very low, less than 0.10 percent (AHPRA, 1985). Formononetin content of 'Junee' is low, about 0.10 percent (Mackay and Barnard, 1981). 'Karridale' Formononetin content is very low, less than 0.10 per cent (AHPRA, 1985). 'Meteora' contains from 0.20 to 0.35% dry weight of formononetin in the green leaves, which is above the maximum of 0.20% recommended for safety from oestrogenic effects in sheep, but it probably will not cause problems in mixed pastures in the high rainfall areas where the cultivar will be employed (Mackay and Barnard, 1981).

Gildersleeve et al. (1991b) reported rose clover had undetectably low concentrations of isoflavones, but that levels for subclover lines ranged from 0.1-18.5 g/kg, based on high-performance liquid chromatog of methanol extractions from leaves of 42 day old seedlings.

Gildersleeve et al. (1991a) stated that formononetin concentrations occurred in decreasing order: 'Woozenellup' > 'Tallabrook' > 'Nangeela' > 'Meteora' > 'Mt. Barker'.

Subterranean clover seed contains 30-40% protein (McGuire, 1985).

There have never been any observed cases of bloat by sheep or cattle grazing subclover, even in the purest of stands, confirmed by Monte Bell, Farm Advisor Emeritus, Glenn Co., CA. (Fred Thomas, pers. comm.)

Subterranean clover interferes little with workers because of its rather low stature (Duke, 1981; Bugg, pers. comm.).

Bugg et al. (1991a) conducted a field trial in southern Georgia concerning 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 and lentil, later on subterranean clover (which harbored pea aphid [Acyrthosiphon pisum {Harris}]), still later on narrow-leafed lupin, then hairy vetch, and lastly on mustard and collard. Bigeyed bugs, mainly Geocoris punctipes (Say), were abundant from late March through late April on 'Vantage' vetch, lentil, and in monocultures of hairy vetch and crimson clover. Berseem and arrowleaf clovers, hairy vetch/ryegrass, and 'Mt. Baker' subterranean clover remained green later than did many other crops and exhibited exceptionally-high densities of bigeyed bugs on June 2nd. 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. Lygus were notably scarce on subterranean clover, which lacks floral and extrafloral nectar, and the developing seeds of which are below ground and inaccessible.

Field trials by Bugg et al. (1990b) in southern Georgia indicated that during April and early May, Lygus lineolaris (Palisot de Beauvois) (tarnished plant bug) attained relatively-high densities on the hybrid vetch (cv '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 adult 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 laboratory 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. 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 southern Georgia, Bugg et al. (1991a) investigated the use of dying mulches" of cool-season cover crops to enhance biological control of insect pests on succeeding spring plantings of cantaloupe (Cucumis melo L. var. reticulatus Seringe). 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) 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) 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 'Vantage' vetch. Rye was particularly poor habitat for G. punctipes.

Subterranean clover can be subject to heavy damage by insects. (Bade et al., 1988) and is attacked by blue alfalfa aphid (Acyrthosiphon kondoi) and by various mites (McGuire, 1985). Cv 'Green Range' shows some tolerance of blue-green aphids (Acyrthosiphon kondoi Shinji) (AHPRA, 1985). Cv 'Junee' is moderately susceptible (Mackay and Barnard, 1981), and cv 'Karridale' is only moderately tolerant but shows above-average resistance to redlegged earth mites, Halotydeus destructor (Tuck) (AHPRA, 1985).

In greenhouse tests, 'Enfield' was tolerant to spotted alfalfa aphid, semi- tolerant to the blue green aphid and very susceptible to pea aphid (AHPRA, 1985).

Nematodes have been found on subclover roots in California and Australia, but their economic significance is unknown (Murphy et al., 1976). Duke (1981) listed the following plant-parasitic nematodes as having been isolated from subclover: Aphelenchoides pareitinus, Heliotylenchus dihystera, Meloidogyne exigua, Meloidogyne incognita, M. hapla, M. javanica, Monohystera stagnalis, Pratylenchus zeae, P. pratensis, and Rotylenchus brevicaudatus. All twelve cultivars tested by Pung et al. (1988) were good hosts for Meloidogyne arenaria; subterranean clover also is susceptible to root knot nematode Meloidogyne incognita.

Kouame et al., (1989) reported that very limited genetic resistance is available to root-knot nematodes among subterranean clover lines. Evaluation of 134 line of subterranean clovers showed that these have limited resistance to Meloidogyne spp., which collectively constitute the most important group of plant-parasitic nematodes. This could indicate problems for succeeding vegetable crops.

Whitehead (1992) stated that in a pot study, burr medic and several other annual Medicago spp. (e.g. barrel medic) showed good resistance to the lucerne (alfalfa) race of stem nematode (Ditylenchus dipsaci). Subterranean clover was deemed very resistant, rose clover resistant, and berseem susceptible.

Duke (1981) listed the following fungi as having been isolated from subterranean clover: Cercospora medicaginsis, C. zebrina, Erysiphe communis, E. polygoni, Kabatiella caulivora, Pellicularia filamentosa, Physoderma trifolii, Pleospora herbaum, Pseudopeziza trifolii, Pseodoplea trifolii, Rhizoctonia solani, Sclerotinia homeocarpa, S. trifoliorum, Sclerotium bataticola, Uromyces trifolii. Duke (1981) further mentioned that stem rot is the most serious disease, with powdery mildew and leaf rust less important.

Seed of cv 'Seaton Park' exhibits embyo dormancy, which prevents germination despite permeable seedcoat and imbibition of water. This appears to have some value in protecting seed from microbial attack as well as out-of-season germination (Archer, 1990).

Clover scorch, caused by the fungus Kabatiella caulivora, and root rots, caused by Pythium and/or Fusarium species, are the primary subclover disease problems in Australia (Smith and Roquette, Jr., 1988).

Mackay and Barnard (1981) reported that relative clover scorch resistance (Scale: 1 to 10, increasing resistance) was as followed:

'Enfield' was suggested for areas where 'Woogenellup' suffers severe damage from clover scorch (Mackay and Barnard, 1981).

In Western Australia, 'Green Range' has shown good winter and spring production and good persistence. It should be a suitable scorch-resistant replacement for cv 'Woogenellup' over much of that cultivar's range in Western Australia, excepting perhaps the wetter fringe and coastal areas where cv. Karridale may be better suited (AHPRA, 1985).

'Meteora's' resistance to clover scorch, together with its tall habit and high spring yield, makes this cultivar well suited to high rainfall areas, particularly those where cattle production and fodder conservation are part of the farming system (Mackay and Barnard, 1981).

Powdery mildew (Erysiphe polyoni) is quite common as a very thin, white, powdery growth on leaves of subclover in coastal areas in late spring (Murphy et al., 1976).

Subterranean clover is subject to damage by root rot by the fungi Pythium, Fusarium, and Rhizoctonia, and to the viral diseases clover stunt, bean yellow mosaic, and red leaf (McGuire, 1985).

Mackay and Barnard (1981) wote that 'Enfield' is more tolerant to clover scorch than 'Woogenellup' but is slightly less tolerant than 'Daliak' and 'Esperance.' It shows symptoms of the disease but there are fewer lesions per petiole than with 'Woogenellup' and the sward suffer less damage

Cv 'Esperance' tolerates root rot (Pythium spp.) better than do cvv 'Seaton Park,' 'Woogenellup' and 'Mt. Barker.' 'Esperance' is an alternative to clover scorch-resistant cultivars 'Seaton Park,' 'Dinninup,' and 'Woogenellup' (Mackay and Barnard, 1981).

According to AHPRA (1985), cv 'Green Range' resists clover scorch, Kabatiella caulivora and may resist or escape from subterranean clover mosaic virus. 'Green Range' is, however, highly susceptible to rust, Uromyces trifolii. Tolerance is intermediate for the main clover root rot organisms in Western Australia, Pythium, Rhizoctonia and Fusarium. That tolerance is inferior to that of cvv 'Daliak,' 'Dinninup,' and 'Junee,' and slightly inferior to that of cv 'Karridale,' but substantially better than that of cvv 'Woogenellup' and 'Mt Barker'

'Howard' is resistant to clover stunt virus (Murphy et al., 1976).

As reported by Mackay and Barnard (1981), cv 'Junee' shows good resistance to clover scorch, Kabatiella caulivora. In four years of field tests in Western Australia, it has been consistently as tolerant to the root rot complex (Pythium, Rhizoctonia and Fusarium) as the most-tolerant present cultivars, 'Daliak' and 'Dinninup.' Cv 'Junee' is not tolerant of root-rot where the main pathogen is Phytophthora. In some experimental plots 'Junee' has appeared very susceptible to powdery mildew, Erysiphe polygoni. However, this will probably not be a significant problem in the areas for which it is likely to be recommended.

'Karridale' resists clover scorch, Katabiella caulivora, well. It shows above-average resistance to the complex of clover root rot organisms, Pythium, Rhizoctonia and Fusarium, prevalent in Western Australia. Also, it is slightly inferior to that of cvv. 'Daliak,' 'Dinninup,' and 'Junee,' slightly better than that of cv. 'Green Range,' and much better than that of cvv. 'Woogenellup' and 'Mt. Barker.' Data from Tasmania suggest moderate resistance to subterranean clover red leaf virus (AHPRA, 1985).

Cv 'Meteora' is the most resistant (superior to 'Trikkala' and 'Larisa') of all the yanninicum cultivars to clover scorch, and it shows resistance as a seedling. It is at least equally tolerant to root rots in the field in Western Australia as are 'Trikkala' and 'Larisa,' and is better than 'Yarloop' (Mackay and Barnard, 1981).

Hochman et al. (1990) reported that, based on detailed replicated field trials in New South Wales, Australia, decline of subterranean clover on acid soils was related to root rot caused by the fungal pathogen Phytophthora clandestina and by low P availability. Liming did not reduce disease incidence, and on one site led to decreased P availability, where soil pH was elevated above 5.5.

Barbetti and Nicols (1991) in Perth, Western Australia, evaluated the subterranean clover varieties 'Green Range', 'Karridale', 'Mt. Barker', 'Mulwala' and 'Woogenellup' for reduction of yield caused by the rust pathogen Uromyces trifolii-repentis. The trial involved one block with the pathogen inoculated and unchecked and another block that was repeatedly sprayed with the fungicides benomyl oxycarboxin to control rust and powdery mildew pathogens. The high-disease block was treated repeatedly with benomyl to control powdery mildew fungus (Erysiphe polygonii). Yield reduction by rust for varieties in descending order: 'Green Range' (25.9%), 'Mt. Barker' (24.8%), 'Woogenellup' (20.3%), 'Mulwala (18.7%), and 'Karridale' (15.2%). 'Larisa' was not affected. Seed yield reduction was as follows: 'Green Range' (89.4%), 'Mulwala' (84.8%), 'Karridale' (70.2%), 'Woogenellup' (67.2%), 'Mt. Barker' (39.5%-not significant). Again, 'Larisa' was unaffected.

Subterranean clover tolerates close grazing, and its large seeds confer easy establishment and early fall production; it can also suppress weeds with its thick cover (Bade et al., 1988). Finch & Sharp (1983) mentioned that weed control is usually required during establishment of subterranean clover because it is a poor competitor. Therefore, competing weeds should be mowed to a height of 2-4 inches. Mowing or grazing are important in weed control (Graves et al., 1986; Miller et al., 1989), with the preferred height being under 4 inches.

Evers and Smith (1988) reported that good stands of subclover quickly form a thick canopy that compete well with other plants. Thin subclover stands show weed problems. Planting sites with low weed densities helps avoid problems. Residual herbicides could be a problem. Early land preparation permits weed seed germination and destruction before planting clover. A spring mowing, after winter weeds flower but before seeds are produced, reduces subsequent weed densities.

Enache and Ilnicki (in press) conducted a study of subterranean clover (cv 'Nangeela') grown as a living mulch for sweet corn (Zea mays L., cv 'Midstates 747'). A field experiment, conducted over 3 years (1986-1988), involved two factors: (1) type of mulch including subterranean clover living mulch, dead mulch of cereal rye (Secale cereale L.), and no mulch; (2) type of tillage including conventional, minimum, and no tillage. Subterranean clover living mulch effectively controlled ivyleaf morningglory (Ipomoea hederacea [L.] Jacq.). The living mulch did not suppress fall panicum (Panicum dicotomiflorum Michaux) in 1986 but did so during the subsequent two years. Weed biomass was reduced by all living mulch combinations. Corn silage and grain yields from the no-tillage + living mulch treatment were comparable to, or higher than, those obtained with the conventional tillage + no mulch treatment.

A field trial by Katz and Ilnicki (1989) assessed soybean (Glycine max [L.] Merr. cv 'Pella') production as affected by a subterranean clover intercrop. Two factors were evaluated: (1) Cover crop: subterranean clover or fallow; and (2) Management of cover crop: double disking, seeding barley, glyphosate for control of subterranean clover and weeds, and an untreated check. Subterranean clover led to reduced yield by soybean but did not effect stand density. Subterranean clover reduced weed biomass by as much as 90%.

Enache et al. (1989) evaluated subterranean clover (Trifolium subterraneum L., cv 'Nangeela') as a living mulch for sweet corn (Zea mays saccharata L., cv 'Seneca', 'Paleface', 'Biqueen', and 'Crossword'). Mowing and three preemergence herbicides were considered for value in weed control: cyanazine alone, and cyanazine, atrazine, and metolachlor applied in combination. Weeds at the site included yellow nutsedge (Cyperus esculentus L.), fall panicum (Panicum dichotomiflorum Michaux), large crabgrass (Digitaria sanguinalis L.), and barnyardgrass (Echinochloa crus-galli [L.] Beauv.). Subterranean clover used as a living mulch provided excellent weed control. Weed control and yields were best for 'Biqueen'. Mowed clover outperformed unmowed clover in terms of weed control and yield. Cyanazine applied alone injured the corn crop slightly and reduced yields. All other herbicide treatments gave better weed control and consistently high yields. Yields from living mulch treatments were either equal to or slightly lower than those for herbicide-treated conventional tillage, but higher than those for untreated conventional tillage.

Enache and Ilnicki (1989) evaluated subterranean clover (Trifolium subterraneum L., cv 'Nangeela') as a living mulch for corn. Field experiments, conducted over 2 years (1986-1987), involved two factors: (1) type of mulch: subterranean clover living mulch, dead mulch of cereal rye (Secale cereale L.), and no mulch; (2) type of tillage: conventional, minimum, and no tillage. Weed control by subterranean clover living mulch was rated good to excellent in 1986 for ivyleaf morningglory (Ipomoea hederacea [L.] Jacq.), velvetleaf (Abutilion theophrasti Medicius), horseweed (Conyza canadensis L.), and jimsonweed (Datura stramonium L.). During 1987, control was good to excellent for iveyleaf morningglory, common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and common ragweed (Ambrosia artemisifolia L.). The living mulch did not suppress fall panicum (Panicum dicotomiflorum Michaux) in 1986, but did so during 1987. Total weed biomass was greatly reduced in all living mulch combinations. Conventional tillage + no mulch performed best in terms of corn grain yields and silage, but economic analysis showed better net performance by living mulch + no tillage.

Guerrero and Williams (1975) conducted growth chamber studies involving filaree (Erodium botrys) and subterranean clover (Trifolium subterraneum cv 'Woogenellup') grown in sole and mixed cultures in a phosphorus-deficient range soil (from Butte County) and in sand with differing levels of supplemental nitrogen, phosphorus, and sulfur. Filaree dominated if phosphorus was limiting, whereas subterranean clover did so if nitrogen were left out of the fertilizer. Subterranean clover has a higher requirement for phosphorus than does filaree, and also appears less capable of exploiting insoluble phosphatic sources. Addition of superphosphate to rangeland soils is suggested as a means of promoting subterranean clover.

Moore et al., (1989) concluded that, based on pot experiments in Australia, subterranean clover can suppress the seedlings of the perennial weed St. John's Wort by overtopping the seedlings and shading them out. This confirmed earlier (1942) findings that subterranean clover could suppress the weed if sown into native pastures, particularly if phosphate fertilizers had been applied. The importance of maintaining a closed canopy of subterranean clover during the early phase of weed seedling growth is emphasized.

'Meteora' is highly competitive with grasses and other herbs and maintains a high clover percentage in hay cuts (Mackay and Barnard, 1981).

Cv 'Koala' appeared particularly good at suppressing weeds in a preliminary trial of 11 cultivars of subterranean clover in southern Georgia (Bugg, pers. comm.).

Vegetational cover data were measured for cover crops in a replicated trial (r=4) at the Blue Heron Vineyard (Fetzer Vineyards), Hopland, Mendocino County, California, May, 1991. Vegetational cover data (Mean % +/- S.E.M.) were as follows: 'Koala': 94.5+/-3.3%; 'Dalkeith': 87.5+/-4.3%; 'Trikkala': 96.3+/-1.2%; 'Mt. Barker': 96.3+/-1.3%; 'Seaton Park': 92.5+/-2.5% (Bugg et al., 1996).

Weed above-ground biomass data (dry) were taken in a replicated study (r=4) at Blue Heron Vineyard (Fetzer Vineyards), Hopland, Mendocino County, California. Cover crops were seeded in late October, 1990; harvest was on May 15-16, 1991. Dominant winter annual weeds were chickweed, shepherds purse, rattail fescue, and annual ryegrass. Data were as follows (Mg/ha, Mean +/- S.E.M.): 'Koala': 0.086+/-0.086; 'Dalkeith': 2.3+/-0.03; 'Trikkala': 1.6+/-0.7; 'Mt.Barker': 0.6+/-0.3; 'Seaton Park': 0.9+/-0.4 Mg/ha (Bugg et al., 1996).

From Nedlands, Western Australia, Cotterill (1990) reported that subterranean clover (cv 'Seaton Park') produced less dry matter biomass early (by the equivalent of December 15 here) but had produced more by the equivalent of March 7 here than 'Serena' burr medic. A mixture of the grasses Bromus diandrus, Hordeum leporinum, Lolium rigidum, and Vulpia myuros reduced growth by both legumes.

From Nedlands, Western Australia, Cotterill (1990) reported that subterranean clover (cv 'Seaton Park') produced less dry matter biomass early (by the equivalent of December 15 here) but had produced more by the equivalent of March 7 here than 'Serena' burr medic. A mixture of the grasses Bromus diandrus, Hordeum leporinum, Lolium rigidum, and Vulpia myuros reduced growth by both legumes.