A couple of crops with exotic-sounding names may be inching closer to commercial production in California.
University of California researchers are reporting progress on guayule, a plant that can produce natural rubber, and kenaf, a potential source of newsprint.
Guayule, a desert shrub, was a source of natural rubber early in this century before synthetic rubber became popular and again during World War II when rubber was scarce. Its use declined after the war, but researchers now are trying to see if guayule can become a profitable cash crop again.
One way that might be possible is to adapt guayule so the plant can provide more than one harvest a year.
Would Increase Productivity
“To succeed as a commercial crop, guayule must become more productive, and the prohibitive cost of . . . transplanting seedlings must be reduced,” three University of California scientists said.
So they studied the abilities of various sources of guayule to regrow.
“Cultivars (varieties) that can regrow after cutting at ground level are expected to make multiple harvest of guayule a reality,” the scientists reported in California Agriculture, a magazine that describes the university’s farming research.
In studies at Shafter in the southern San Joaquin Valley, they found that one new variety of guayule, C250, “responded favorably to harvest at ground level: 98.1% of the plants harvested in three consecutive years survived and grew.”
Perhaps because of this, C250 produced the highest rubber yield of the six varieties tested, 830 pounds per acre.
“The finding that some selections respond favorably to harvest at ground level and are capable of surviving and regrowing vigorously may influence the way guayule is harvested in the future,” said the article by Ali Estilai, associate research agronomist at UC Davis; Himayat H. Naqvi, associate specialist, and J. Giles Waines, botany professor at UC Riverside.
But they added that either rubber yield from guayule or the current rubber price of about $1.10 per kilogram must be increased before the crop can become commercially profitable.
The researchers predicted that more productive cultivars will be developed within 5 to 10 years through breeding and high biomass-production techniques.
“While the price of natural rubber depends on world supply and demand, as well as global politics, increasing the productivity of the plant remains biologically feasible,” they concluded.
In the same issue of California Agriculture, another UC researcher discussed an experiment to determine if kenaf could grow profitably in the arid Imperial Valley in the southeastern part of the state.
Newspaper industry officials are studying kenaf as a potentially cheaper source of newsprint than trees. Paper from kenaf fiber was used to print 83,000 copies of the Bakersfield Californian in an experiment in July, 1987.
Most kenaf research has been conducted in Texas, but the crop may be adaptable to California because previous work has produced yields of 16 tons per acre in the San Joaquin Valley.
Kenaf varieties were planted at the university’s Imperial Valley Agricultural Center near Holtville between 1983 and 1986 and irrigated with Colorado River water. The same varieties also were planted in a fine sand desert area in 1985 and were irrigated with ground water that contained higher salt concentrations.
Cut in Yield
“The kenaf varieties grown in the desert with higher salinity irrigation water showed a substantial reduction in yield,” said the report by Frank E. Robinson, a water scientist with the agricultural center.
In fact desert yields ranged from just 11% to 20% of those at the agricultural center, indicating “that kenaf is at least moderately sensitive to saline irrigation water,” Robinson says.
But most of the kenaf grown at the agricultural station produced yields of 9 to 9.5 tons per acre, which Robinson found encouraging and potentially profitable.
“The upper yield range is approximately 9.5 tons dry weight of stalks per acre and may improve with additional work on cultivation practices and genetic selection,” the report says. “Yields of this magnitude have encouraged the construction of a kenaf paper mill in southern Texas.”