Opportunities To Grow Our Own Rubber

Irvin C. Feustel, Frederick E. Clark.

After Pearl Harbor, the Japanese got control of the sources of about 90 percent of our natural rubber. Had it not been for remarkable achievements in the production of synthetic rubber, the consequences would have been most serious.

Our dependence on a limited area in the Far East for nearly all our natural rubber had long been a matter of concern. Attempts to establish plantations of Hevea rubbertrees (Hevea brasiliensis) in Mexico were made as early as 1910. The Firestone Rubber Co. started plantings of these trees in Liberia about 1925. The Ford Motor Co. made plantings in 1928 in Brazil. In 1935, the Goodyear Tire & Rubber Co. entered on a similar venture in Panama and later in Costa Rica. However, the production of tree rubber in the Western Hemisphere has been seriously curtailed by the South American leaf blight. Adequate methods for control of the leaf blight are essential for success in establishing large plantations.

The United States is unsuited climatically to the growth of both the Hevea and the Castilloa rubbertrees (Castilla elastica), although attempts have been made by the Department of Agriculture to grow the rubbertrees in Florida. Some of the trees were able to survive, but they did not produce enough latex to be profitable.

Consumption of natural rubber in the United States rose gradually to775,000 long tons in 1941. In 1945; consumption dropped to 105,429 tons. The production of synthetic rubber was very small before 1943, but climbed steadily to a peak of 761,699 tons in 1946. In 1947, the use of natural and of synthetic rubbers was practically the same. Since then the proportion of natural rubber consumed has increased. The trend in 1950, however, was again toward a sharp increase in synthetic-rubber consumption because of unsettled international conditions. The use of reclaimed rubber, including natural and synthetic, has been fairly constant around 200,000 to 300,000 tons for the past 10 years. Our total consumption of new natural and synthetic rubbers is presently about half of the world total. Approximately 70 percent of the rubber used in the United States goes into tires.

Confronted by a critical shortage of rubber in 1942, the 77th Congress passed Public Law 473, which directed the Department of Agriculture to plant 75,000 acres of guayule, a rubber-yielding shrub, to carry out cultural and processing research, and to construct and operate mills for the extraction of the rubber. The program was called the Emergency Rubber Project.

Workers in the Intercontinental Rubber Co., which had produced rubber from wild guayule shrubs in Mexico since 1905 and from cultivated guayule shrubs in California since 1925, had proved that guayule would grow in limited areas in California, Arizona, and Texas. The company had also selected a supply of seed from high-yielding strains developed by the late W. B. McCallum, chief botanist of the company. The Government bought the entire United States holdings of the Intercontinental Rubber Co., with headquarters at Salinas, Calif., in order to obtain the benefit of the existing rubber-producing facilities for the Emergency Rubber Project. These included nurseries, plantations, a small assay laboratory, a mill for processing the shrubs, research files, and patents.

The Forest Service was charged with the administration of the project-and with responsibility for large-scale cultural and processing operations. The Bureau of Plant Industry, Soils, and Agricultural Engineering was designated to conduct research, within its usual field of endeavor, on all phases of plant production. The Bureau of Agricultural and Industrial Chemistry was called on to improve the existing process for recovering rubber from guayule and to develop methods of extracting it from other domestic plants. The Bureau of Entomology and Plant Quarantine, the Weather Bureau, the Soil Conservation Service, the Agricultural Adjustment Administration, State experiment stations, and universities also participated in the program.

Most of the authorized plantings were in California, the first near Salinas. At one time plans were developed to plant 400,000 acres of guayule, principally in California and Texas. To avoid competition with food production, however, only 32,000 acres were actually under cultivation at the end of the Second World War. Improvements were made in the Salinas mill, and another mill was erected at Bakersfield.

About 1,400 tons of rubber was produced from Texas wild shrubs and California cultivated shrubs before Congress ordered the liquidation of the Emergency Rubber Project at the close of the war. Much effort went into research and development designed to improve cultural practices and the steps involved in the extraction of rubber. Wild shrubs in Mexico supplied about 7,000 tons of rubber a year during the war, thus greatly depleting that country's reserves. Because of the shortage of water for irrigation, the outlook for cultivated guayule shrubs there is not good. Mexico apparently cannot be counted on to supply much guayule rubber for some years.

It was assumed that the need for the domestic production of natural rubber would end with the war. But a postwar appraisal showed that, despite advances in the technology of synthetic elastomers, a big part of the Nation's civilian and military needs could be met only by natural rubber. Because of the uncertainty of a constant supply of plantation rubber from the Far East, it seemed advisable to establish a small but sound and readily expandable source of natural rubber within the United States.

GUAYULE and other domestic plants can provide our strategic natural-rubber reserves if their economic production can be assured. Indications are that economic production may be accomplished through further improvements in culture and processing. Guayule particularly has promise of being a valuable supplementary crop in several Southwestern States that are marginal for other cultivated crops because of drought.

Shortly after the close of the Emergency Rubber Project, the Office of Naval Research and the Stanford Research Institute entered a contract to provide funds and facilities for renewed activity. Long-range, fundamental studies on guayule and other rubber-bearing plants were envisaged. Research on the genetics and physiology of guayule plants was initiated in October 1946, under the leadership of Stanford Research Institute. A study of the biochemistry of rubber formation was subcontracted to the California Institute of Technology. A similar arrangement was made with Oregon State College to plant kok-saghyz for seed production. On August 1, 1947, after termination of the contract between the Office of Naval Research and Stanford Research Institute, Congress authorized and appropriated funds, under the Strategic and Critical Materials Stockpiling Act, for continuation of the program under the Department of Agriculture. These funds established the Natural Rubber Research Station at Salinas, Calif. The program was expanded to include research on rubber extraction and processing.

Research on crop production, genetics, and related activities is assigned to the Bureau of Plant Industry, Soils, and Agricultural Engineering; research on the development of new or improved methods for extraction and processing of rubber to the Bureau of Agricultural and Industrial Chemistry.

Guayule now appears to be the most practical rubber-producing plant that can be grown in the United States. Kok-saghyz (the Russian dandelion) is regarded as the second-best prospect. Research on other plants, among them cryptostegia (a rubbervine native to Madagascar), goldenrod, milkweed, pingue, and rabbitbrush, has given less promising results. Hundreds of other plants in the United States contain rubber, but in too small amounts to be of practical. interest.

GUAYULE (Parthenium argentatum) was known to the early Indians in Mexico. It was first noted scientifically in 1852 near Escondido Creek, Tex., by J. M. Bigelow, a physician attached to a Mexican boundary survey. Guayule was first described botanically by Professor Asa Gray of Harvard some years later. Public attention was drawn to guayule rubber, apparently for the first time, by an exhibition at the Centennial Exposition in Philadelphia in 1876. Production of rubber from native wild plants began in Mexico in 1902. The Texas Rubber Co. began operations at Marathon, Tex., in 1909. About 9,000 tons of guayule rubber was imported from Mexico in 1910 one-fifth of the total rubber consumption of the United States at that time.

Guayule is a semidesert shrub, which somewhat resembles the sagebrush. It grows wild in north-central Mexico and in the adjacent Big Bend section of Texas. It prefers a well-drained, light soil. As indicated by its natural range, the plant needs a mild climate, although it has survived temperatures of 5 F. or below.

Guayule resists drought and will grow with a rainfall of only 10 to 15 inches a year. It responds readily to more favorable conditions of moisture.

The guayule plant may live for 30 years or longer. It probably accumulates rubber during most of its lifetime. The deposition of rubber, however, appears to be greatly stimulated by conditions that interrupt growth of the plant periodically, such as low temperatures or drought. If moisture and temperature are conducive to growth during most or all of the year, a large plant with little rubber results. Under domestication, the economical peak of rubber production is reached during early maturity. The recommended cropping period is about 4 years on irrigated land and 5 or 6 years on non-irrigated land. Yields range from 900 to 1,500 pounds of crude rubber to the acre.