This plant has been called sour clover (Madson, 1951; Duke, 1981; McLeod, 1982), sourclover (Duke, 1981), bitter melilot (McLeod, 1982), annual yellow clover (McLeod, 1982), bitter clover (Nelson, 1922; McLeod, 1982), King Island melilot (McLeod, 1982), Indian sweetclover (Duke, 1981), and senji (Duke, 1981).

Melilotus spp. are not true clovers (Taylor, 1985).

Melilotus indicus (L.) All. (Munz, 1973); Melilotus indica (L.) All (Duke, 1981).

According to Duke (1981), some cultivars of sourclover have low coumarin concentrations; 'Fo. S. I.' was mentioned as having especially great biomass production (nearly 10 Mg/ha).

The seed of this variety closely resembles that of alfalfa, and care should be exercised to see that it is free from seed of noxious weed pests. In 1922, much of the seed was obtained from screenings of wheat; such seed should be carefully recleaned. In many cases from five to twenty percent of the seed proves to be hard and will not germinate the first year (Nelson, 1922).

Sourclover has a high proportion of hard seed, and there are from 250,00-275,000 seeds/lb (Duke, 1981).

In the first few weeks of growth, sourclover closely resembles alfalfa (Nelson, 1922).

Duke (1981) described this species as an annual herb with erect stems up to 50 cm tall, branching, sparingly pilose, leaves trifoliate, stipules often with a small tooth near base; petioles up to 2 cm long, rachis about 5 mm long, 9 mm wide, coarsely toothed; rounded at the apex; racemes many flowered, up to 10 cm long, including peduncle up to 3 cm long; bracts subulate, ca. 0.5 mm long; pedicels ca. 1 mm long, reflexed after flowering; calyx ca 1.5 mm; corolla yellow, ca 2.5 mm long; style 0.9-1.2 mm long; pod 3-4 mm long, 2-3 mm wide, one-seeded, with prominent reticulate veins.

Munz (1973) described the species as follows: Stems erect, 2-8 dm high, glabrous or +/- appressed pubescent; petioles commonly 0.5-2 cm long; stupules lance-subulate, 4-6 mm long; leaflets cuneate-oblanceolate to -obovate, 1-3 cm long, obtuse or truncate, denticulate; racemes 2-10 cm long, including the peduncles; pods ovoid, reticulate, glabrous, 1.5-2 cm long.

This erect, stemmy plant bears small yellow flowers in short, dense racemes (Madson, 1951). The stalk is woody (McLeod, 1982).

Sourclover has been said to be frost tolerant and withstands mean annual temperatures of 7.2-22.5 C, with a mean of 18 cases of 14.8 C (Duke, 1981). Madson (1951) credited the species with moderate cold resistance, and McLeod (1982) stated that it withstands frost better than either common vetch or Canadian field pea, yet is not winter hardy. It grows well during the winter in southern California, San Joaquin, Sacramento Valleys, and in other areas suitable for alfalfa where the minimum temperature does not go below about 18 F (Nelson, 1922).

Sourclover originated in the Hindustani Center of Diversity, and ranges from the Cool Temperate Steppe to Wet through Subtropical Dry Forest Life Zone; it is native to the Mediterranean Region south to Ethiopia, and to Central Asia and India (Duke, 1981). Sourclover is often a weed in North America, in the Sonoran zone from Oregon south to Baja California, Mexico (Duke, 1981). Munz (1973) wrote that it is common in low-elevational waste places in most of California.

Sourclover is most valuable from central California south. In the northern half of the state, cold winters preclude satisfactory growth. It has been used extensively in southern California, particularly in orchards (Madson, 1951).

McLeod (1982) stated that this species can be grown anywhere in the U.S., and that it does especially well in the Southwest.

Sourclover tolerates annual precipitation of 0.9-12.9 dm, with the mean of 18 cases being 7.6 dm (Duke, 1981). After sowing, irrigation should be immediate and be repeated 7-10 days later; sourclover can be sown into standing water; 2-3 irrigations are sufficient for the crop (Duke, 1981). It has a heavy, succulent foliage, and a high water requirement (Nelson, 1922).

In dry-farmed fruit culture, do not allow souclover to continue growth in spring after exhaustion of free water in the soil (Nelson, 1922).

Sourclover does best with about 200 lbs of superphosphate per acre at seeding. Fertilizers are often unnecessary (Nelson, 1922).

Sourclover tolerates a pH range of 5.0-8.2, with a mean of 6.8 for the 17 cases assessed; the species is said to tolerate alkali, high pH, and limestone (Duke, 1981) and to have a high lime requirement (McLeod, 1982).

Sourclover does well in a wide range of soil types, but it does best on well-drained neutral or alkaline soils of medium to high fertility (Duke, 1981). Madson (1951) recommended loam to heavy soil types, whereas Nelson (1922) stated that growth was best on sandy loams, although a wide variety of soils are suitable. McLeod (1982) wrote that almost any soil is suitable, but loams are best; the deep, large taproot was credited with the ability to break up heavy soils.

Sourclover tolerates 3-6 mmhos of salinity or 5-8 in gypsiferous soils (Duke, 1981).

Maranon et al. (1989) found that salinity tolerance during germination was directly related to seed weight in three species of annual Melilotus spp. from the Guadalquivir delta in Spain. The rank order was M. messanensis > M. segetalis > M. indica (sourclover). Within-species differences were also found among several populations of M. segetalis and M. indica, which was related to the habitat of the mother plant.

Sourclover is an annual (Madson, 1951; Nelson, 1922) plant that is self pollinated (Duke, 1981). Seed is sown from September through November and harvested for forage from February to April, when plants are in full flower (Duke, 1981). Munz (1973) listed the flowering period in California as being from April through October.

Seeding rates recommended include 20-25 lb/a (Nelson, 1922), 40-50 kg. ha (Duke, 1981), 10 to 15 lbs/acre (McLeod, 1982), and 15 to 25 lbs/acre (Miller et al., 1989).

2-25% of the seed may be hard and will not germinate the first year (Nelson, 1922).

Sow at a depth of 1/2 inch (McLeod, 1982).

Sourclover seed requires scarification prior to sowing because there is a high proportion of hard seed; the seedbed should have a fine tilth (Duke, 1981).

Sow on the dry soil mulch in orchards rather than in moist soil just after irrigation, as is a common practice for peas and vetches. Where furrow irrigation is used, furrows should be sufficiently close to completely wet the soil surface; otherwise, a poor stand may result. Irrigation after seeding usually firms the soil enough to insure good germination. The seed bed should be prepared as for alfalfa, and the seed either broadcasted or drilled. After planting, the soil should be firmed over the seed sufficiently to insure an ample supply of moisture for proper germination (Nelson, 1922).

Sourclover should be seeded from September through November (Duke, 1981). In California, seeding should be from October to November (Madson, 1951). In southern California, it should be sown by October 15th to be ready for incorporation by March (McLeod, 1982).

According to Nelson's (1922) account, in orchards where spring plowing is done in February or March, sow by September 15th. Where adequate water for irrigation is available and late spring plowing is practiced, December 1 sowings may suffice. In dry-farmed fruit culture, seed after the first fall rains, and do not allow continued cover crop growth in spring after the free water in the soil has been exhausted.

Sourclover requires type "A" Rhizobium for inoculation (same as for alfalfa) (Duke, 1981).

Nelson (1922) recounted that sourclover grew well all over California, requiring inoculation only on soils farmed without legumes for many years.

Madson (1951) listed seed cost as low.

Seed was formerly abundant and cheap (Madson, 1951) but has been unavailable in the trade from 1989 through 1992 (Cantisano, pers. comm.; Bugg, pers. comm.)

Sourclover requires about 150 days to enter full flower (Duke, 1981), and Munz (1973) listed flowering in California as occurring from April through October.

Munz (1973) listed flowering as occurring from April through October, which suggests that mature seed probably is being produced from May through November (Bugg, pers. comm.).

Sourclover seed yields are only about 250 kg/ha in India (Duke, 1981), but McLeod (1982) stated that the species is a heavy seed producer. Seed is easy to produce where the species is adapted (Madson, 1951).

The seed remains viable for a relatively long period of time (McLeod, 1982).

This is an erect, stemmy plant similar in its habit of growth to other sweet clovers; it shows moderate density of growth (Madson, 1951).

Various estimates of height are presented: A few inches to several feet depending on environment (Madson, 1951); a maximum height of about 50 cm (Duke, 1981); and 20-80 cm (Munz, 1973).

Sour clover has a much more extensive root system than vetch or pea. Six months after planting, tap roots were found to a depth of eight feet (Nelson, 1922). Therefore, sourclover is believed valuable for opening up heavy soils (Madson, 1951).

Establishment may be aided by growing in mixture with oat or barley (Duke, 1981). Weeding in the early stages is useful; manuring usually does not help stand establishment (Duke, 1981).

Weeding in the early stages is useful; manuring usually does not help stand establishment (Duke, 1981).

Sourclover can be mowed 2-4 times and is harvested from February - April in India (Duke, 1981).

Nelson (1922) indicated that the stage at which the crop should be incorporated depends on soil type and moisture supply. On heavy soils, aeration is crucial and sourclover is best incorporated when it is mature and bulky. Thorough incorporation is important to facilitate breakdown. With dry soils, irrigate immediately after plow-down, to reduce drought stress to orchard trees. In annual farming systems, allow two to four weeks to elapse before planting successive cash crops.

Nelson's (1922) account indicated that when cover cropping twice in immediate succession on medium to light-textured soils, both cover crops may be disked in. Deep placement of residue is not so important for decomposition if the surface is shaded during the summer months as it is under clean culture. On heavy (clayey) soils, deep incorporation of residue is best. Decomposition requires from two to four weeks and is fastest in light-textured (sandy) soils. Inadequate soil moisture can delay decomposition two or three months or even longer.

According to Duke (1981), in India, sourclover is harvested for forage from April through June, when in full flower and after seed formation has begun. There may be 2-4 cuttings.

Sourclover has served as a green manure and cover crop in the orchards of southern and central California, particularly citrus (McLeod, 1982).

By 1922, sourclover was recognized as one of the leading winter cover crops for California (Nelson, 1922), and in tests by the Agricultural Experiment Station of the University of California at Riverside, it out-yielded common vetch and Canadian field pea, the two legumes most commonly grown for winter green-manure crops. It is also was widely successfully as a summer cover crop, and the Agricultural Extension Service encouraged its use.

Sourclover was used extensively in southern California, particularly in orchards but was replaced by bare chemical fallow. Sour clover was easy to grow where adapted, and seed was abundant and cheap (Miller et al., 1989).

Sourclover is used for reclaiming saline areas (Duke, 1981).

Sourclover is often used in mixes with barley or oat (Duke, 1981), and Young (1922) reported a cover crop of sourclover (Melilotus indica, 30 lb/a) mixed with rye (Secale cereale, 10 lb/a) and some purple vetch (Vicia benghalensis) grown in a citrus orchard.

Sourclover cultivar 'Fo. S.I.' yields nearly 10 MT/ha in green forage, and overall sourclover biomass yields are 4.5-7.5 MT/ha in India (Duke, 1981).

Experiments conducted in southern California showed that Sourclover outyields common vetch and Canadian field pea (McLeod, 1982).

Nelson (1922) stated that above-ground biomass production compares well with that of any of the green-manure crops tested in California. Yields of green matter average about ten tons per acre under favorable conditions. In a test vineyard in Fresno County, more than forty tons per acre were obtained, but such yields are unusual. Yields are occasionally much below average.

Sourclover hay contains 3.36% N (Duke, 1981). Projecting from the 4.5-7.5 Mg/ha and 10 Mg/ha biomass figures given above, this translates to 151-252 kg N/ha and 336 kg N/ha.

Sourclover hay contains 0.49% P2O2, 1.5% K2O, and 2.49% CaO (Duke, 1981).

Werenfels et al. (1963) conducted unreplicated field observations in long-term cover crop plots that had been established in 1924 and managed consistently until 1961 in an apricot orchard on a Yolo loam soil in Davis, California. The researchers suggested that infiltration rates (ring infiltrometers) were in descending order: alfalfa (Medicago sativa) > 'Hubam' white sweetclover (Melilotus alba) > sour clover (Melilotus indicus) > cereal rye (Secale cereale) > clean cultivation. The researchers stated that the alfalfa and white sweetclover alleviated a plow pan, but that cereal rye did not. Unfortunately, the unreplicated nature of the study severely limits interpretation.

Young (1922) conducted an unreplicated study upon which have been based many subsequent generalizations about cover-crop effect on temperatures in citrus groves. A 6-acre grove was divided into 2, 3-acre sections. A cover crop of sourclover (Melilotus indica, 30 lb/a) mixed with rye (Secale cereale, 10 lb/a) and some purple vetch (Vicia benghalensis) was established. Locations of two temperature stations were assigned based on similarity of low temperatures when dense cover crops were present in both sections. On January 18, 1922, the northern half of the orchard was ploughed, but the cover crop in the southern half was left intact. Conditions were wet during this study. Temperature measurements were made for 16 nights of frost, including the exceptionally-cold spell from Januay 19-23, which included the coldest weather in southern California since 1913. Sheltered thermometers showed that 10 inches above the ground, the cover-cropped plot was, on average, approximately 2 degrees F colder than the clean-cultivated plot during the night. The only effect at 5 feet above ground was to decrease the rate of temperature rise during the morning. Unsheltered thermometers showed that depression of minimum temperatures was about 2.4 degrees F at 7 inches above the ground, and 0.4 degrees F at 24 inches above the ground. At times when air temperatures were falling rapidly, the temperature at 7 inches could be as much as 11 degrees colder in the cover-cropped plot. The results suggest that cover crops do increase the risk of frost, but only slightly.

Nelson (1922) found that sour clover improves heavy soils physically and increases the water-holding capacity of all soils. It retains moisture in the fertile surface strata, thus sustaining soil life. The deep taproot and extensive root system penetrate into the subsoil and relieve plow pan, which is common in orchards. In orchards frequently cover cropped with tap-rooted plants, water penetration is greatly improved.

Werenfels et al. (1963) conducted unreplicated field observations in long-term cover crop plots that had been established in 1924 and managed consistently until 1961 in an apricot orchard on a Yolo loam soil in Davis, California. The researchers suggested that infiltration rates (ring infiltrometers) were in descending order: alfalfa (Medicago sativa) > 'Hubam' white sweetclover (Melilotus alba) > sour clover (Melilotus indicus) > cereal rye (Secale cereale) > clean cultivation. The researchers stated that the alfalfa and white sweetclover alleviated a plow pan, but that cereal rye did not. Unfortunately, the unreplicated nature of the study severely limits interpretation.

Duke (1981) discussed the use and potential problems of sourclover as cattle feed. In the Southwest, sourclover is less productive and palatable than 'Hubam' annual white sweetclover. Sourclover is used as green forage for cattle and cows, and as a maintenance ration for heifers; it is also grown for silage . As green feed, the analysis is 3.3% protein, 78.4% moisture, 6.4% fiber, and 14.4% total digestible nutrients. As silage, there is 2.1% protein, 70.2% moisture, 14.1% total digestible nutrients. As hay, the analysis indicates 18.6% protein, 10% moisture, and 23.8% crude fiber. If sourclover is cut before bloom and used for feed, bloat is more likely than if it is cut during flowering. Chopped forage should be fed in mixtures with other dry forage. If sourclover is fed alone or in excess to cattle, it can cause health problems such as lethargy, tympanitis, and paralysis, and taint the milk. Coumarin is a chemical imparting the bitter flavor to sourclover, but low-coumarin varieties are available.

Unlike those of its congeneric relatives white and yellow sweetclover, sourclover blossoms does not attract nectarivorous predatory and parasitic insects (Bugg, pers. comm.). Sourclover is resistant to aphids (McLeod, 1982).

The following nematodes have been isolated from sourclover: Ditylenchus dipsaci, Heterodera marioni, and Tylenchorhynchus martini (Duke, 1981).

Duke (1981) listed 18 pathogenic fungi, 1 bacterium (Pseudomonas meliloti, and pea mosaic virus as attacking sourclover. The fungi mentioned included powdery mildew, downy mildew, and Sclerotium rolfsii.

Sourclover may require some initial weeding; it is often grown in mixture with barley or oat, which are sometimes used as weed-suppressive nurse crops with other legumes (Duke, 1981).