Kenaf
P.J. LeMahieu1, E.S. Oplinger2, and D.H. Putnam3
1Agrecol, 4906 Femrite Drive, Madison, WI 53716.
2Department of Agronomy, College of Agricultural and Life Sciences and
Cooperative Extension Service, University of Wisconsin - Madison, WI 53706.
3Department of Agronomy and Plant Genetics, University of Minnesota,
St. Paul, MN 55108.
April, 1991.
I. History:
Kenaf (Hibiscus cannabinus L.) is a fiber plant native to east-central Africa
where it has been grown for several thousand years for food and fiber. It is a common
wild plant of tropical and subtropical Africa and Asia. It has been a source of
textile fiber for such products as rope, twine, bagging and rugs. Kenaf is a promising
source of raw material fiber for pulp, paper and other fiber products, and has been
introduced since WWII in China, USSR, Thailand, South Africa, Egypt, Mexico and
Cuba.
Research in the United States to use the kenaf bast (outer bark) fibers for rope
began in the 1940's when jute imports from Asia were interrupted by World War II.
In the 1950's, the Agricultural Research Service (ARS) of the U.S. Department of
Agriculture screened more than 500 plant species as potential fiber sources for
pulp and paper manufacturing. As a result, kenaf was selected as the most promising
nonwood fiber plant for this use. Continued research resulted in the development
of high yielding, anthracnose resistant varieties. Today, research and development
continues, primarily in Texas, Oklahoma, Mississippi and Southeastern U.S.A., with
emphasis on development for newsprint manufacture.
II. Uses:
A. Fiber Uses:
Kenaf has a unique combination of long bast and short core fibers which makes it
suitable for a range of paper and cardboard products. Scientists at the ARS have
tested several kenaf pulping techniques, with the pulps being used to make several
grades of paper including newsprint, bond, coating raw stock and surfaced sized.
Results have been positive, particularly in terms of paper quality, durability,
print quality and ink absorption.
Commercialization of kenaf for newsprint manufacturing is in its final stages. Commercial
scale newsprint runs were conducted by the private sector in California, Texas and
Florida. Newspapers made from kenaf pulp have been shown to be brighter and better
looking, with better ink laydown, reduced ruboff, richer color photo reproduction
and good print contrast. Quality analyses showed kenaf newsprint to have superior
tear, tensile and burst ratings. Additionally, kenaf newsprint manufacturing requires
less energy and chemicals for processing, an important advantage, both economically
and environmentally.
B. Forage Uses:
The top leafy portion of the kenaf plant is not useful for pulping. Therefore, this
part of the plant would be useful as forage if harvest equipment could be practically
adapted to a dual collection operation.
Florida researchers found that immature plants at a height of 6 ft contained up
to 20% protein. The kenaf ensiled successfully, both alone and with corn, and the
silage was acceptable to heifers. They also found that kenaf leaf, dried and ground
into a meal, had a greater crude protein digestibility than that of alfalfa meal.
The amino acid composition of kenaf leaves is similar to that of alfalfa.
Oklahoma research showed that kenaf leaf and petiole (non-stalk) portions of the
plant were readily consumed by lambs and contained low fiber and high N concentrations.
Analysis of the leafy kenaf material showed values of 8.7% NDF, 3.5% ADF and 34.0%
CP. Contrasted to this, total plant composition levels were 42.9%, 32.6% and 17.1%
respectively. Clearly, the leaf and petiole portion of the plant contains the majority
of the digestible nutrients.
C. Food Uses:
Where kenaf is grown in home gardens for fiber, the more tender upper leaves and
shoots are sometimes eaten either raw or cooked.
III. Growth Habits:
Kenaf is a member of the mallow (Malvaceae) family, with okra and cotton
as relatives. Kenaf plants grown in dense stands are largely unbranched and grow
to a height of 8 to 14 ft and under certain conditions will reach 20 ft. The stem's
outer bark contains the long soft bast fibers which are useful for cordage and textiles.
Bast fibers make up 20 to 25% of the stem on a dry weight basis. Beneath the bark,
a thick cylinder of short woody fibers surrounds a narrow central core of soft pith.
Stem color of most varieties is green, but there are several red-stemmed and purple-stemmed
accessions. Leaf shape varies considerably. While the first few leaves of kenaf
seedlings are not lobed, some varieties develop post-juvenile leaves that are very
deeply lobed. The root system is very extensive, with a deep tap root and widespreading
lateral roots.
Kenaf plants produce large cream-colored flowers only after day length reaches approximately
12.5 hours in the fall. Flower production is indeterminate. Kenaf is primarily self-fertile,
but is considered an often cross-pollinated crop. Seeds are dark grayish-brown,
flattened triangular shaped, 5 to 6 mm long. There are roughly 15,000 to 20,000
seeds/pound.
IV. Environment Requirements:
A. Climate:
The kenaf plant is said to have a wider range of adaptation to climates and soils
than any other fiber plant in commercial production. Kenaf yields have been highest
in regions with high temperatures, a long growing season and abundant soil moisture.
It is quite sensitive to cool temperatures and grows slowly when temperatures are
below 50oF.
Kenaf has performed well in the Gulf Coast region and the far southeastern United
States. Yields in the Midwest U.S. have been high at times, but inconsistent. Length
of frost-free season and availability of solar radiation may limit economic production
of kenaf fibers in northern locations. Variety development for tolerance to cool
air and soil temperatures could greatly expand kenaf's area of productive adaptation.
B. Soils:
Kenaf is adapted to a wide range of soil types, but performs best on the heavier,
well drained, fertile soils. Kenaf does not perform well on soils with severe drainage
problems. Prolonged periods of standing water, particularly during the seedling
stage, can severely inhibit growth.
V. Cultural Practices:
A. Seedbed Preparation:
Kenaf seeds are relatively small and require good seed-soil contact for germination.
Therefore, a fine, firm, well-prepared seedbed is necessary. Given the success of
raised-bed kenaf production in Texas, ridge-till planting may be an effective option
in northern areas.
B. Seeding Date:
Recommended planting dates are similar to those for soybeans. Warm, moist soils
after danger of a killing frost has passed are the ideal planting conditions. Planting
too early often results in poor emergence and slow, non-competitive growth. Planting
too late will often result in reduced yield potential due to reduced solar radiation
availability.
C. Method and Rate of Seeding:
The preferred plant population, row width and planting method may vary according
to production region, growing conditions and cultivar used. More research is needed
to determine interactions among these factors (particularly cultivar/population
interactions) and to determine yield improvement potential through modification
of these factors.
A harvest plant population of 75,000 to 100,000 plants/acre is generally recommended.
However, as the crop is moved north, narrower rows and a population range of 100,000
to 120,000 plants/acre may be more desirable. Plants in stands that are too dense
for the cultivar or seasonal growing conditions tend to be short, spindly and weak-stemmed.
Plants in stands that are too sparse produce lateral branches that are too heavy.
In both cases lodging is inevitable. Row spacing decisions should consider probable
weed problems and control measures, harvest method and plant population goal.
Seed should be planted less than 1 in. deep if the soil moisture and seedbed texture
are suitable. Kenaf can emerge from a depth of 2.5 in. under the most favorable
conditions. The importance of high quality seed (germination over 80%), and equipment
that gives uniform seed placement and good seed-soil contact cannot be overemphasized.
D. Fertility Requirements:
Kenaf's response to added fertilizers depends on soil nutrient levels, cropping
history and other environmental and management factors. A range of fertility responses
have been reported. In general, added nitrogen has increased kenaf yields. Some
important considerations:
1 - Fertility programs should focus on vegetative needs rather than grain/reproductive
needs. Kenaf, unlike cotton, for example, produces a vegetative fiber rather than
a fruiting fiber.
2 - Kenaf, with its deep tap root and widespreading lateral root system, is considered
to be an excellent user of residual nutrients from previous crops.
3 - At harvest, kenaf leaves are left in the field. It has been estimated that this
leaf material can return from 50 to 100 pounds of nitrogen/acre.
E. Variety Selection:
In the U.S., the varieties used most extensively are those developed by ARS researchers
in Florida - `Everglades 41' and `Everglades 71'. Both varieties are resistant to
anthracnose. Since their development in the 1960's, there has been little variety
development activity, although the ARS is initiating new breeding efforts. Genetic
improvements for adaptation to northern environments may be feasible.
F. Weed Control:
In the southern U.S., kenaf emerges and grows so rapidly that it competes effectively
with weeds. In cooler climates and with earlier planting dates, cultural and/or
chemical weed control measures are more important. One weed species which is especially
competitive with kenaf is velvetleaf, a relative of kenaf. At the seedling stage,
velvet leaf and kenaf are very similar in appearance and rate of growth. Fields
with high populations of this weed are not recommended for kenaf production.
Satisfactory weed control and crop tolerance have been demonstrated for many of
the common preplant-incorporated, preemergence and postemergence herbicides. Special-Local-Need
labeling, leading to full registration, is being pursued in some states.
Cultivation and other postemergence tillage practices such as rotary hoeing can
be effective in controlling weeds. In the absence of herbicide registration for
kenaf, and particularly in cooler climates which inhibit rapid early plant growth,
mechanical weed control should be used.
G. Diseases and Nematodes:
Growers and researchers have found kenaf to be resistant to most plant diseases.
Anthracnose is perhaps the most serious potential disease problem. The variety development
work done by the ARS in Florida was very effective in breeding and selecting for
anthracnose resistance. Damping-off is a moderate concern during seedling stages
and seed treatments are being tested and registered for use.
Nematodes are viewed in some areas as the most serious constraint to kenaf production.
In cotton growing areas, the root-knot nematode/fusarium wilt complex is expected
to limit yield potential for both cotton and kenaf, and will create crop rotation
challenges due to the common susceptibility of the two crops.
H. Insects:
There has been little economic damage to kenaf by insects in experimental production
fields. Potential insect problems could arise in the early stages of seedling emergence
and development. However, the kenaf plant tolerates a fairly high population of
chewing and sucking insects, and since the production emphasis is biomass rather
than root, seed, fruit or flower, the required level of insect protection for kenaf
may be much less than for most commercial crops.
I. Harvesting, Drying and Storage:
Several harvest and storage methods have been tested. The preferred system will
likely vary from one area to another because of differences in climate and milling
requirements. Until recently, the most feasible method appeared to be chopping the
green or air-dried plants with a forage chopper. The green material can be stored
anaerobically like silage and the air-dried material can be piled or loosely stacked
or baled.
The most recent innovation has been the development of an 8-row harvest machine
which cuts the stalks and lays them down for drying in the field. The dried stalks
are gathered, shredded at the field and transported to the fiber mill's storage
area.
VI. Yield Potential:
Yields in research plots have varied widely, from 2.5 ton/acre at Rosemount, Minnesota,
to 15 ton/acre at College Station, Texas. One-acre blocks at Fort Gibson, Oklahoma
yielded nearly 10 ton/acre in 1988. Commercial scale production in Texas has produced
dry-weight yields of 7.5 ton/acre under irrigation and 6.0 tons/acre on dryland.
Fiber production field trials in the southeast U.S. have shown that kenaf can yield
three to five times more fiber/acre/year than southern pine. With U.S. annual consumption
of newsprint at over 12 million tons (1988), and with 60% of that volume imported
at a cost of approximately $4.5 billion, the further commercialization of kenaf
as a source of paper pulp would appear promising. However, successful commercialization
will be dependent upon local cost comparisons which will consider economies of scale,
transportation costs and local processor demand.
VII. Economics of Production and Markets:
Successful introduction of any new crop depends on establishment of markets for
the raw and processed crop materials, in concert with development of production
areas. There appear to be significant markets for kenaf fibers in the manufacture
of pulp, paper and paperboard products, and as synthetic fiber substitutes. Projections
show that by the year 2000, over one million acres of kenaf would be needed annually
to supply just the increase in U.S. newsprint demand over 1990 levels, without reducing
the volume of newsprint imports or the consumption of wood fibers.
Production of kenaf as an industrial raw material will necessarily be locallized
in the same region as processing facilities. The unprocessed crop is too bulky to
be transported great distances. As with many processed food crops, the actual price
that producers receive for raw product will be determined by contract negotiation
between them and the processors. That price must consider production costs, the
comparable risks and profits of producing conventional crops and the comparable
prices paid by potential customers for traditional fiber supplies. A producer would
also need to consider kenaf's impact on government programs and its effects on crop
rotations and on productivity of other crops in a rotation.
VIII. Information Sources:
"Cultural and Harvesting Methods for Kenaf... An Annual Crop Source of Pulp
in the Southeast". Production research report no. 113, 1970. Agricultural Research
Service, United States Department of Agriculture, Washington, D.C.
"General Feasibility Study: Kenaf Newsprint System". 1982. C.S. Taylor,
G.L. Laidig, and R.W. Puls. Prepared for American Newspaper Publishers Association
by Soil and Land Use Technology, Inc., Columbia, MD.
"Growers Handbook for Kenaf Production in the Lower Rio Grande Valley of Texas,
U.S.A." 1989. Kenaf International (in cooperation with the U.S.D.A. Cooperative
State Research Service and Agricultural Research Service), McAllen Texas.
"Kenaf Newsprint: Realizing Commercialization of a New Crop After Four Decades
of Research and Development". 1988. Daniel E. Kugler, Cooperative States Research
Service, U.S.D.A. Washington, D.C.
"Kenaf - A Promising Crop For Agriculture". 1986. U.S.D.A.-Office of Critical
Materials. Washington, D.C.
"Kenaf Research, Development and Commercialization". 1989. Proceedings
from the Association for the Advancement of Industrial Crops Annual Conference,
October 5, 1989. Prepared by the Office of Agricultural Industrial Materials, Cooperative
State Research Service, U.S.D.A.
"Potential New Crop: Kenaf, Commercial Fiber and Pulp Source". January
1979 - December 1989. Quick Bibliography Series: QB 90-33. 214 Citations from AGRICOLA.
Jerry Rafats, National Agricultural Library. Beltsville, Maryland.
Dempsey, J.M. 1975. Fiber Crops . Pages 203-304. The University Press of
Florida. Gainesville, Florida. 457 pages.