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Brigham, R.D. 1993. Castor: Return of an old crop. p. 380-383. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Castor: Return of an Old Crop

Raymond D. Brigham

  1. HISTORY OF PRODUCTION IN THE UNITED STATES
  2. THE PLANT
  3. AGRONOMY
    1. Adaptation
    2. Cultural Practices
  4. INSECTS AND DISEASES
  5. HARVESTING
  6. NEEDS AND FUTURE PROSPECTS
  7. REFERENCES
Production of castor (Ricinus communis L., Euphorbiaceae) is needed in the United States to supply castor oil for the hundreds of products using this versatile chemurgic raw material. Forty to 45 thousand tonnes of castor oil and derivatives are imported each year (Roetheli et al. 1991) to supply the entire needs of our domestic industries. The United States is the largest importer and consumer of castor oil in the world. Castor oil is classed as a strategic material critical to our national defense by the Agricultural Materials Act P.L. 98-284 passed by Congress in 1984. Other "strategic" materials include natural rubber and sperm whale oil substitutes. Public Law 81-774 requires that sufficient supplies of these materials be acquired and stored in the United States to meet national defense needs in case of war (Roetheli et al. 1991).

HISTORY OF PRODUCTION IN THE UNITED STATES

Castor was in production as early as the mid-1850s in the central part of the United States, and over 23 crushing mills reportedly were operational at that time (Zimmerman 1958). Sporadic production caused mills to eventually locate on the east and west coasts to crush imported seed. In the mid-1930s, Baker Castor Oil Company began a program to develop domestic production to supply their processing plant in California. Contracts were offered to growers, and limited production developed in the Imperial and San Joaquin Valleys (Zimmerman 1958). During World Wars I and II, domestic production was encouraged because of castor oil's strategic value. Derivatives of castor oil are key ingredients in hydraulic fluids, greases, and lubricants for military equipment. During the Korean conflict, castor production was stimulated by a government sponsored procurement program. The production area reached over 20,000 ha in 1951, mainly in Texas, Oklahoma, California, and Arizona. Improved cultivars and harvesting equipment allowed the crop to compete favorably with other field crops. By 1959, Texas became the leading producer of castor, and production was centered near Plainview (Brigham and Spears 1961). In the late 1960s, over 30,000 ha were grown in Texas. The seed was shipped to the crushing facility of Baker Castor Oil Company, Bayonne, New Jersey. A small crushing facility with solvent extraction was built in Plainview in the early 1960s by the Plains Cooperative Oil Mill of Lubbock. This plant operated until castor production ceased in the early 1970s. Castor production and processing was discontinued due to: (1) low world prices for castor oil; (2) higher prices being paid for competing crops grown in the High Plains area; (3) the cooperative oil mill and castor oil buyers not agreeing on a contract price for the oil in 1972, and (4) elimination of the government price support for castor in 1972. Since that time, only limited plantings for seed production have been made. Some planting seed of the cultivar 'Hale' was exported to other countries during the 1980s.

THE PLANT

Although commonly referred to as a "bean," castor is not a legume. The plant has also been called the "castor oil plant." Castor oil, one of the oldest commercial products, was used in lamps by the Egyptians more than 4,000 years ago, and seeds have been found in their ancient tombs (Weiss 1971). Castor is considered by most authorities to be native to tropical Africa, and may have originated in Abyssinia (Weiss 1971).

Although grown as annual plants, they act as perennials in the tropics and subtropics and the plants reach heights of 9 to 12 m. The dwarf-internode cultivars 'Hale' and 'Lynn', and hybrids using them as the pollen parent, vary in height from 0.9 to 1.5 m, compared to 1.8 to 3.7 m for the normal-internode types formerly grown (Brigham 1970a,b). Soil conditions, availability of moisture, and levels of nutrients can cause considerable variation in height of plants. Plants have a tap root, plus prominent lateral roots below the soil surface.

The large leaves are palmately lobed, (hence the name Palma Christi used for castor) and are borne more or less alternately on the stems, except for the two opposite leaves at the node just above the two cotyledonary leaves. The petioles are usually several times as long as the long axis of the leaves. The main stem is terminated by the first or primary raceme, which often is the largest on the plant. The primary raceme of early dwarf-internode cultivars usually occurs after the 6th to 10th node. On later cultivars, the primary raceme may occur after the 8th to 16th node. In introductions from other countries, dwarf-internode types flowering after 40 or more nodes are known.

After the first raceme appears, branches originate at the nodes below it. The number of branches depends on plant spacing and in some cases the cultivar. Under field conditions, two or three branches occur at almost the same time, but generally in the following order: the first branch at the node immediately beneath the primary raceme, the second at the second node, and the third at the third node below the primary raceme. The first racemes formed on the branches are commonly called the "second set" of racemes. Subsequent branches arise from the nodes just beneath the racemes of the second set. This sequence of development continues as long as the plant remains alive and growing actively. Thus, the development of racemes along any one axis is sequential, making it possible for a plant to have racemes in all stages of development from bud stage to complete maturity.

Typically, the racemes usually bear pistillate flowers on the upper 30 to 50% and staminate flowers on the lower 70 to 50% of the raceme. Number of staminate and pistillate flowers can vary greatly, depending upon raceme size. The flowers are without petals. After the pollen is shed, the staminate flowers dry up and usually drop. The pollen, which is discharged forcibly from the anthers, is carried to stigmas mainly by wind (Brigham 1967). After fertilization, the pistillate flowers develop into spiny capsules, though spineless types are known. At maturity, the hull (pericarp) of the capsule may split along the outside seam (dorsal suture) of each of the three capsule segments (carpels). If splitting is violent, as in wild types, the seed will be ejected and scattered on the ground around the plant. This type of splitting (dehiscence) is not present in cultivars grown for mechanized production. Seeds of present cultivars are held within the capsule for several weeks after frost with no appreciable loss.

Seeds of current cultivars weigh from 3.0 to 3.5 g. Seed color ranges from light to dark brown, with various mottling patterns. The seed coat makes up about 25% of the weight of the seed. Oil content averages 50% on a dry weight basis.

Chromosome number of castor is 2n = 20. Autotetraploids have been produced using colchicine, and haploids have been reported, but in nature, castor is found mainly in the diploid form. There is little or no loss of vigor when castor plants are inbred (Moshkin 1980).

AGRONOMY

Adaptation

Highest yields of castor are produced under irrigation on fine or medium textured soils, and where low relative humidity prevails. Areas where soils are infested with the cotton root-rot fungus should not be considered for growing castor, because the plants are highly susceptible to this disease (Brigham and Spears 1961). At least a 140-day growing season is required (from planting until first killing frost) to produce satisfactory yields of castor seed, and a 150 to 160-day season is more desirable.

Cultural Practices

Seedbed preparation is similar to cotton, maize, sorghum, soybean, and other row crops. Deep tillage, such as chiseling 20 to 30 cm deep, encourages development and deeper penetration of the tap root. Castor is usually planted in a shallow furrow by opening a bed with a lister-type planter, or planting can be on low beds. Beds usually are irrigated before planting by running water down the furrows. Land should be prepared for 0.96 to 1.01 m rows to fit the available harvesters.

Castor should be planted when the soil is warm--a 10 day average of 15.6°C at 20 cm depth at 8 a.m. In the Plainview, Texas, area, May 5 to 25 is usually satisfactory. Castor should not be planted after June 10 in that area. Only seed of high germination and of good quality should be planted to assure timely emergence and adequate plant populations. Seed treatment materials may be applied if needed to control damping-off in cold soils.

Castor seeds are large and slow to germinate; emergence of the seedlings may take 7 to 14 days. Castor seeds require moist soil over a longer period than maize or cotton. Seeds should be planted 6.3 to 7.6 cm deep, depending on texture and condition of the soil. If press wheels are used in contact with the seed, care should be taken that they do not crush the seed. Castor is planted in 0.96 to 1.01 m rows, with a seeding rate of 11.2 to 15.7 kg/ha and plant spacing of 20 to 25 cm within the row. Special care must be taken to prevent crushing the fragile seed in the planter box. Air planters are ideal, and can space seeds precisely. Use of an inclined-plate planter is also a preferred method, but a cotton planter box can be used if properly modified (Brigham and Spears 1961).

Adequate amounts of nitrogen, phosphorus, and potassium must be available to produce high yields of castor seed. Levels of these nutrients should be determined by soil test. If the soil is deficient in nitrogen, 90 to 135 kg/ha of nitrogen usually are needed for maximum yields. A split application of nitrogen is often used, with the second half sidedressed between the rows at last cultivation. If phosphorus is needed, application should be made before planting time. Potassium can be applied at planting time. A minimum of 37 to 56 kg/ha of P is needed for production of castor, and 15 to 19 kg/ha of K.

Where preplant furrow irrigation is applied, castor plants should not require irrigation until the first racemes appear on the plant. Under normal conditions, 12 to 14 days between irrigations should keep plants from stressing for moisture, but high temperatures and high winds during the peak growing and fruiting periods may cause the plants to need more frequent irrigation. Castor requires 20.6 to 24.7 cm/ha of water annually to produce high yields. The time of last irrigation is usually from 1 to 10 Sept.

Cultivation is much the same as for controlling weeds in cotton or soybeans. Rotary hoes are often used before or after the plants emerge to control small annual weeds and grasses. Cultivation with sweeps should be as shallow as possible to prevent damage to the fibrous root system of the plants. Trifluralin is labelled as a preplant incorporated herbicide for control of certain broadleaf weeds and grasses.

INSECTS AND DISEASES

The castor plant is not toxic to most insects, even though small amounts of the toxic protein, ricin, and the alkaloid tricinine, occur in vegetative parts of the plant (Weiss 1971). However, only infestations of false chinch bugs have become serious enough to warrant control measures in the Texas High Plains, and those occur only in a few fields every few years. Thrips, corn earworms, armyworms, spider mites, leaf miners, lygus bugs, and green stink bugs have been observed in castor fields with minimal damage.

Castor plants are attacked by numerous diseases under high relative humidity conditions, but only a few occur in the High Plains area. Alternaria leaf spot, caused by Alternaria ricini (Yoshii) Hansf., caused defoliation to varying degrees of earlier susceptible cultivars, but later released cultivars such as 'Hale' and 'Lynn' (Brigham 1970a,b) show resistance to this fungus. Bacterial leaf spot, caused by Xanthomonas ricinicola (Elliott) Dowson, also caused serious damage to susceptible cultivars, but the above dwarf-internode cultivars have moderate resistance to bacterial leaf spot. Gray mold, caused by Botryotinia ricini (Godfrey) Whetzel, has been observed a few times in the Plainview area, but has never been considered a problem. The organism causing cotton root rot, Phymatotrichopsis omnivara (Duggar) Hennebert, attacks castor, and plants should not be grown on infested soils. Charcoal rot, caused by Macrophomina phaseolina (Tassi) Goidanich, has been observed on plants that were stressed for soil moisture. Capsule mold, incited by a complex of fungi, causes capsules to stop development and turn bluish-purple or brown to black. This only occurs after high rainfall periods, so is usually not a problem on the High Plains. The dwarf-internode castor cultivars are resistant to Verticillium wilt caused by Verticillium species (Brigham and Minton 1969).

HARVESTING

Dwarf-internode castor plants are usually ready to harvest about 10 days after a killing frost, if normal drying weather prevails. Capsules should be dry enough for the seed to hull when rubbed between the hands (Schoenleber 1961). The newest harvester has a 4-row header that uses rotating brushes to remove the capsules from the plants. This harvester, adapted to a grain combine, uses rubber-covered cylinders to hull the seed. Ground speed under favorable conditions can be 8 km/hr. Relative humidity must be below 40% when harvesting castor seed, and moisture content of the seed should be 6% or lower. Castor seed stores well, and does not deteriorate significantly in storage for at least 2 years.

Yields of irrigated castor range from 2,242 to 3,363 kg/ha, and some fields have produced 3,811 to 4,035 kg/ha. The seed is usually bought at a price directly related to the world market. There are no government acreage controls or price support programs.

NEEDS AND FUTURE PROSPECTS

To restart domestic production, industries in the United States which are large users of castor oil will need to make contractual agreements on the price to be paid for oil which will attract both grower and processor. To encourage sufficient production of castor seed to supply the castor oil needs of our domestic industries the following factors need to be addressed: If castor production can be stimulated and production can again be realized, research priorities include:

REFERENCES

Last update April 21, 1997 aw