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Webber, C.L. III and R.E. Bledsoe. 1993. Kenaf: Production, harvesting, processing, and products. p. 416-421. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Kenaf: Production, Harvesting, Processing, and Products

Charles L. Webber III and Robert E. Bledsoe*


  1. LADONIA MARKET CENTER
    1. Demonstration Projects
    2. Production
    3. Harvesting
    4. Processing and Product Development
  2. FORAGE EVALUATION
    1. Materials and Methods
    2. Results and Discussion
  3. SUMMARY
  4. REFERENCES
  5. Table 1
  6. Table 2

Kenaf (Hibiscus cannabinus L., Malvaceae) is a warm season annual closely related to cotton (Gossypium hirsutum L.) and okra (Abelmoschus esculentus L.). Initial interest in kenaf in the United States was as a domestic supply of cordage fiber as a jute substitute in the manufacture of rope, twine, carpet backing, and burlap (Wilson et al. 1965). Later, kenaf was identified as a very promising fiber source for production of paper pulp (Nieschlag et al. 1960; White et al. 1970). Researchers have processed kenaf fibers into both newsprint and bond paper (Bagby et al. 1979; Clark et al. 1971). Agricultural research starting in the early 1940s focused on the development of harvesting machinery, high yielding anthracnose resistant cultivars, and cultural practices for kenaf as a cordage crop (Nieschlag et al. 1960; White et al. 1970; Wilson et al. 1965).

In addition to the use of kenaf for paper pulp and cordage, researchers have investigated its use as an animal feed (Killinger 1967; Phillips et al. 1989, 1990; Webber 1990b), a poultry litter (Tilmon et al. 1988), and as a bulking agent for sewage sludge (Webber 1990a). Additional products that could possible use kenaf as a raw material include automobile dashboards, carpet padding, corrugated medium (Kugler 1988) and as a "substitute for fiberglass and other synthetic fibers" (Scott and Taylor 1988).

The United States acceptance of kenaf as a commercial crop would be strengthened if additional uses for kenaf can be established in the United States. These and other possible kenaf uses need to be further investigated to increase the potential use of kenaf plant products in the United States and therefore encourage the commercial establishment of the kenaf industry.

LADONIA MARKET CENTER

Demonstration Projects

Starting in 1988, the Ladonia Market Center, Ladonia, Texas, has conducted kenaf research, development, and demonstration work. In addition to expanding the list of possible uses of kenaf fibers, the Ladonia Market Center is a primary proponent of kenaf as a livestock feed. Kenaf demonstration projects have included kenaf production, harvesting, processing, and product evaluations.

Production

Fiber and Forage. In addition to cooperative research with the USDA evaluating kenaf cultivars and their protein content, the Ladonia Market Center was involved in a demonstration project evaluating the effect of row spacings on kenaf dry matter yields. Production size (10 ha) kenaf plantings produced 10.3 t/ha on 25-cm row spacings and 14.0 t/ha on 76-cm row spacings when harvested at 97 days after planting as a forage crop.

Seed. Ladonia Market Center has also demonstrated the feasibility of producing seed from photo-insensitive kenaf cultivars in northern Texas. Typically, photosensitive kenaf cultivars are preferred for use in the production of kenaf fiber in the United States. Two of these cultivars, 'Everglades 41' and 'Everglades 71', were developed by USDA researchers (Wilson et al. 1965) to extend the growing season of kenaf plant before the plants initiate flowering. These photosensitive cultivars initiate flowering when daylengths decrease to approximately 12.5 h, mid-September in southern states (Scott 1982). In photosensitive cultivars, the initiation of flowering results in plant growth reductions (Dryer 1967). Because of late floral initiation and inability to produce mature seed prior to a killing frost, seed production in the United States for these cultivars is limited to southern Florida, the Lower Rio Grande Valley of Texas, and southernmost Arizona and California (Scott 1982).

Unlike photosensitive cultivars, photo-insensitve cultivars (i.e. Guatemala series) can initiate flowering and produce mature seed before a killing frost (Dempsey 1975). Photo-insensitive cultivars such as 'Guatemala 4', 'Guatemala 45', 'Guatemala 48', 'Guatemala 51', 'Cuba 2032' can initiate flowering after 100 days and prior to a decrease daylength of 12.5 h (Dryer 1967; Dempsey 1975). Photo-insensitive plants can, therefore, be planted during May or early June and still have ample time to produce mature seed. The earlier production of mature seed for photo-insensitive cultivars greatly expands the potential seed production areas. After floral initiation, photo-insensitive cultivars continue to grow without as much reduction in growth rate as with photosensitive cultivars (Dryer 1967; Webber 1990b). As a livestock feed, kenaf is often harvested at an earlier stage of growth than as a fiber crop, 60 to 90 days after planting (DAP) compared with 120 to 150 DAP (Webber 1990b). A shorter growing season for kenaf as a livestock feed enables a producer to use kenaf cultivars of the photo-insensitive group to produce equivalent dry matter productions as with photosensitive cultivars while using seed that can be produced further north and in a larger geographic area (Webber 1990b). Seed production of photo-insensitive cultivars in more northern areas is often overlooked as a result of the demand for and production of photosensitive cultivar seed which cannot be typically produce outside a few selected southern locations (Scott 1982).

Harvesting

The evaluation of field equipment for use with kenaf continues to be an important aspect in commercializing kenaf. Standard cutting, chopping, and baling equipment can be used for harvesting kenaf as a forage and fiber crop. Kenaf was baled into both small square and large round bales. It is an economic advantage to use presently available commercial harvesting equipment if possible rather than investing in the development and production of kenaf specific equipment. Appropriate harvesting equipment is readily available throughout the United States, and the on-farm cost can be distributed over that of other crops produced on the farm.

Processing and Product Development

Research demonstrated the feasibility of pelletizing kenaf as a fiber and forage crop. Pelletizing kenaf increases the density of the kenaf plant material, reducing both transportation and storage costs. Kenaf stalks and whole plants (stalks and leaves) were pelletized with standard commercial equipment in widespread use for existing livestock feeds. Kenaf stalks with an initial density of 0.31 g/cm3 were transformed into pellets with a 13.2 mm diameter and a density of 1.21 g/cm3, a 390% increase in density. Whole plant kenaf, produced as a livestock feed, was pelletized into pellets with a 10.4 mm diameter and a density of 1.22 g/cm3, a 395% increase in density. The pelletizing research is an important element in moving the harvested kenaf crop from the field to a packaged kenaf product.

In addition to processing and product development work with kenaf as a livestock feed, Ladonia Market Center developed kenaf particle boards (K-Board) of various densities, thicknesses, and fire and insect resistances. Kenaf fibers were also successfully used in product development evaluations with extraction molded plastics.

FORAGE EVALUATION

Kenaf was recognized as having high protein levels and therefore might be a potential livestock feed (Killinger 1964). Crude leaf protein levels in kenaf range from 18 to 30% (Cahilly 1967; Killinger 1967; Killinger 1969; Suriyajantratong et al. 1973; Swingle et al. 1978) stalk crude protein levels from 5.8 to 12.1% (Phillips et al. 1989; Swingle et al. 1978) and whole plant crude protein levels from 11 to 25% (Clark and Wolff 1969; Killinger 1965; Phillips et al. 1989; Powell and Wing 1967; Swingle et al. 1978).

Cahilly (1967) reported that the amino acid composition of kenaf was similar to that of alfalfa (Medicago sativa L.). Kenaf can be ensilaged effectively, and as such has satisfactory digestibility, and an outstanding amount of digestible protein (Wing 1967). Digestibility of dry matter and crude proteins for kenaf feeds have ranged from 53.5 to 82.4%, and 59 to 70.6% respectively (Phillips et al. 1989; Powell and Wing 1967; Suriyajantratong et al. 1973; Swingle et al. 1978; Wing 1967). Kenaf meal, used as a supplement in a rice ration for sheep, compared favorably with a ration containing alfalfa meal (Suriyajantratong et al. 1973). Clark and Wolff (1969) determined that crude protein content of kenaf decreased from 90 to 244 DAP. Powell and Wing (1967) and Hurse and Bledsoe (1989) have reported whole plant kenaf yields of 13.4 and 13.9 t/ha respectively at approximately 98 DAP. The objective of the forage evaluation research was to determine the effect of cultivars and harvest date on plant growth, protein content, and kenaf dry matter yields.

Materials and Methods

In 1989, and 1990, a research study was conducted at Ladonia, Texas (Lat. 33°, Long. 96°) which included six kenaf cultivars and three harvest dates. The six kenaf cultivars evaluated were 'Guatemala 4', 'Guatemala 45', 'Guatemala 48', 'Guatemala 51', 'Cuba 2032', and 'Everglades 41'. Each cultivar was harvested at 76, and 99 DAP to evaluate kenaf as a livestock feed. A full season harvest sample was also collected at 184 DAP (27 Oct. 1989) and 154 DAP (25 Oct. 1990) to comparatively evaluate the cultivars as a source of fiber. The experiments were planted on 26 Apr. 1989 and 24 May 1990. Plots were 3 by 6 m with 50 cm row spacing. A 2.25 m2 (1.5 by 1.5 m) quadrant was harvested from the center three rows of each plot. The plants in the entire quadrant were harvested at ground level and weighed to determine the fresh weight of plants per hectare. Three plants from this area were measured for plant height, and vegetative growth stage (V-Stage). The kenaf vegetative growth stage was determined by adapting the soybean [Glycine max (L.) Merrill] index system developed by Fehr et al. (1971) to kenaf. The index system counts the number on vegetative nodules on the primary plant stalk. Leaves and reproductive parts (flowers and flower buds) were removed and stalks cut into 20 cm lengths. Leaves, reproductive parts, and stalks were weighed before and after being oven dried at 66°C for 48 h. Total dry matter, stalk yields, percent leaves, and percent stalks were based on oven dry weights. Leaf, and stalk samples from harvest dates 76, and 99 DAP were ground using a Wiley mill with a #10 mesh screen and then reground using a #20 mesh screen. The Texas A&M analytical laboratory at College Station, Texas analyzed the ground kenaf leaf and stalk samples for crude protein (Techcon Method 334-74-W/B).

The studies were randomized complete block designs with four replications and mean differences were determined using a least significant difference (LSD) test level of 0.05 as described by Snedecor and Cochran (1967).

Results and Discussion

'Guatemala 4' was shorter than all other cultivars except 'Everglades 41' (Table 1). Vegetative development was greater for 'Guatemala 45' than either 'Guatemala 4' and 'Cuba 2032' (Table 1). Cultivars and harvest dates affected the percentage of kenaf leaves (Table 1). 'Guatemala 45' with 31% leaves was significantly greater than either Guatemala 48 or Everglades 41 (Table 1). Other researchers have also reported significantly less leaf percentages for 'Everglades 41' compare to other cultivars (Wilson et al. 1965; Webber 1990b). Percent leaves decreased 36% for the first harvest to 20% for the third harvest (Table 1). As kenaf plants increase in height and maturity, the lower leaves senesce, resulting in a decreased percentage of leaves (Webber 1990b; Clark and Wolff 1969).

Kenaf cultivars did not affect the percent crude protein in the leaves or stalks (Table 2). Percent whole plant crude protein was the only crude protein percentage which resulted in differences between cultivars (Table 2). 'Guatemala 48' had significantly greater percent whole plant crude protein than 'Cuba 2032' (Table 2). Crude protein for leaves, stalks, and whole plants were adversely affected by harvest date and decreased from 76 DAP to 99 DAP (Table 2).

'Guatemala 48', 'Everglades 41', and 'Cuba 2032' had significantly greater whole plant yields than either 'Guatemala 4' or 'Guatemala 45' (Table 2). The combination of high whole plant protein and whole plant yields for Guatemala 48 resulted in this cultivar yielding the greatest total crude protein produced per ha (Table 2).

The selection of a harvest date and kenaf cultivar are important variables in producing maximum protein and dry matter yields. 'Guatemala 48' percent whole plant protein was greater than 'Cuba 2032' and greater than all other cultivars in its production of crude protein production per ha (Table 2). An early harvest date (76 DAP) produced the greatest percentage leaf, stalk, and whole plant protein (Table 2). Kenaf can produce a large amount of dry matter, 7,512 kg/ha, within 90 DAP (Table 1). Results suggest that kenaf should continue to be studied, not only as a fiber crop for the production of paper pulp, but as a viable source for livestock feed. Future research should focus on differences in percent crude protein between cultivars, and maximizing total protein production per ha.

SUMMARY

The possible acceptance of kenaf as a commercial crop within the United States is increased as additional production, harvesting, processing, and product development evaluations are conducted. The establishment of small diversified uses for kenaf may offer certain advantages over the large capital investment in a single large kenaf paper or newsprint mill. The increased production, processing, and product development work being conducted within private industry is encouraging and suggests a bright future for the establishment of kenaf as a commercial crop within the United States.

REFERENCES


*We acknowledge David A. Iverson, Research Technician, Agricultural Research Service, South Central Agricultural Research Laboratory, Lane, Oklahoma for field plot work, data entry, and data analysis; Vee Hiltbrunner-Bledsoe, Leon Hurse, and Foy Burns for their constant encouragement and support.
Table 1. Two year means of yield components of kenaf as influenced by cultivars and harvest dates.

Variable Height
(cm)
V-Stage
(no.)
Leaves
(%)
Total dry matter
(kg/ha)
Cultivarz
Everglades 41 180 54.4 27 9160
Cuba 2032 185 50.8 28 9195
Guatemala 4 171 50.7 29 7883
Guatemala 45 183 56.1 31 7713
Guatemala 48 187 54.9 28 9345
Guatemala 51 185 52.8 30 8831
LSDy (0.05) 10 4 3 1269
Harvest datex
76 DAP 123 32.7 36 4764
99 DAP 171 48.7 30 7512
169 DAP 252 78.4 20 13788
LSDw (0.05) 7 3 2 898
zCultivar means averaged over three harvest dates.
yLSD for comparison between cultivars.
xHarvest means averaged over six cultivars.
wLSD for comparison between harvest dates.


Table 2. Two year means of crude protein percentages and whole plant protein yields as influenced by cultivars and harvest dates.

Crude protein
Variable Leaves
(%)
Stalks
(%)
Whole plant
(%)
Whole plant
(kg/ha)
Cultivarz
Everglades 41 15.2 3.0 6.9 436
Cuba 2032 14.5 2.6 6.2 435
Guatemala 4 14.4 2.6 6.6 325
Guatemala 45 14.9 2.9 7.2 369
Guatemala 48 15.5 2.8 7.2 558
Guatemala 51 14.9 2.8 6.7 395
LSDy (0.05) NS NS 0.9 116
Harvest datex
76 DAP 15.6 3.2 7.7 390
99 DAP 14.2 2.4 5.9 449
LSDw (0.05) 0.7 0.3 0.5 NS
zCultivar means averaged over two harvest dates (76 and 99 DAP).
yLSD for comparison between cultivars.
xHarvest means averaged over six cultivars.
wLSD for comparison between harvest dates.


Last update April 23, 1997 aw