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Webber, C.L. III. 1996. Response of kenaf to nitrogen fertilization. p. 404-408. In: J. Janick (ed.), Progress in new crops. ASHS Press, Arlington, VA.

Response of Kenaf to Nitrogen Fertilization

Charles L. Webber III

  5. Table 1
  6. Table 2

As a result of inconsistent responses to supplemental nitrogen fertilization and the general absence of kenaf (Hibiscus cannabinus L.) fertility recommendations, research was conducted at Lane, OK, to determine the effect of N application rates of 0 (control) 56, 112, 168, and 224 kg/ha on kenaf yield components. Kenaf cultivars 'Tainung 1' and 'Everglades 41' were planted in May of 1989 and 1990 on a Bernow fine sandy loam soil with a 0%-3% slope. Nitrogen applications did not affect plant height, plant density, or stalk biomass compared to the control. Stalk diameters at 1 m increased with N application rates of 112, 168, and 224 kg/ha compared to the control. Though not significantly different, there was a trend of increased stalk yields up to 168 kg N/ha, while 224 kg N/ha significantly decreased stalk yields compared to 168 kg N/ha. This research demonstrated the importance of determining N requirements for specific production areas without assuming the need for high N applications to achieve maximum yields. It also demonstrated that excess N can have a detrimental effect on stalk yields. Future research should examine the effect of other essential nutrients on fiber quantities and qualities produced on specific soil types.

Kenaf (Hibiscus cannabinus L.), a warm-season annual, was first identified as a potential jute substitute in the manufacturing of rope, twine, carpet backing, and burlap (Wilson et al. 1965). Research demonstrated that kenaf is also a very promising fiber source for production of paper pulp (Nieschlag et al. 1960; White et al. 1970). Kenaf fibers were processed into both newsprint and bond paper (Clark et al. 1971; Bagby et al. 1979). Other potential commercial uses for kenaf are being investigated, such as animal feed (Webber 1993), poultry litter (Tilmon et al. 1988), bulking agent for sewage sludge (Webber 1992), and for oil absorption (Tiller et al. 1994).

As with other crops proper fertility maintenance, especially for supplemental nitrogen application, is needed to optimize kenaf yields, and minimize production cost. Reports so far are inconsistent relative to the effects of N on kenaf stalk yields (White and Higgins 1965); researchers in Georgia have reported both positive (Adamson et al. 1979) and no benefits (Massey 1974). Studies in Florida demonstrated that the positive response to N applications on stalk yields were dependent on soil type (Joyner et al. 1965), where kenaf grown on a sandy soil responded to N and did not respond to N on a peat soil. Bhangoo et al. (1986) in California, and Sij and Turner (1988) in Texas, increased stalk yields with the addition of N to soils with low available nitrogen. Stalk yields in Missouri (Ching and Webber 1993) on a silty clay soil and in Nebraska (Williams 1966) on a silty clay loam soil did not benefit from N applications. Stalk yields have also responded differently to N at the same location and soil between years (Hovermale 1993). In this study the effect of five nitrogen application rates (0, 56, 112, 168, and 224 kg/ha) on kenaf yield components was investigated in order to increase available information in kenaf products.


A two-year field-plot study was conducted at Lane, Oklahoma, on a Bernow fine sandy loam, 0%-3% slope, (fine-loamy, siliceous, thermic Glossic Paleudalf). Each year the N fertilizer treatments (56, 112, 168, and 224 kg/ha) were applied in the form of ammonia nitrate. In addition, the entire research area also received a broadcast fertilizer application of 0N-72P-139K kg/ha, which was incorporated prior to planting. Plots were 3 m wide (four 76-cm rows) and 6 m long. Kenaf cultivars 'Tainung 1' and 'Everglades 41' were planted 2 May 1989, and 23 May 1990. All plots received a pre-emergence application of metolachlor [2-chloro-N-(2-ethyl-6-methlphenyl)-N-(2-methoxy-1-methylethyl) acetamide] at a rate of 1.12 kg ai/ha at planting. The herbicide was applied using a tractor-mounted sprayer delivering 187 liters/ha at 275 kPa pressure. Fan-tip sprayer nozzles were 0.5 m apart on a 3-m boom. All plots were kept weed free by handweeding.

Kenaf plots were hand-harvested on 21 Oct. 1989, 172 days after planting (DAP), and on 19 Oct. 1990, 149 DAP. A 2.25 m2 (1.50 m by 1.50 m) quadrate was harvested from the center rows. Plant population and moisture content were also determined in the harvest area. The harvested plants were cut at ground level and fresh weights were determined. Three plants were randomly selected at 105 DAP and at harvest to determine plant heights. The harvested plants used to determine heights were also measured with calipers to determine stalk diameters at 1 m above ground level.

Leaves, flowers, and flower buds were removed from the stalks and weighed separately before and after the samples were oven dried at 66°C for 48 h. Fresh and oven-dry weights of the three plants were used to determine the percent moisture of the plants and the percent stalks by weight. The plant moisture content and percent stalks were used to convert kenaf fresh weight to dry weight. Stalk yields were based on oven-dry weights. Precipitation was measured at the Lane, OK, research location.

In both years, treatments were arranged in a randomized complete block design with four replications. When the F-test indicated statistical significance at the P = 0.05 level, the least significant difference (LSD) test was used to separate means. In addition, coefficient of linear correlation (r) analysis was used to establish the correlation between various yield components. Since no significant year by treatment by cultivar interactions were indicated results are reported averaged across years.


Total precipitation was 664 mm for the 1989 and 623 mm for the 1990 growing season. The 20-yr average rainfall for the location from 1 May to 31 Oct. is 611 mm. Precipitation during the first half of the 1989 growing season (455 mm) was 214 mm greater than that of the first half of the 1990 growing season (241 mm).

Plant heights, plant populations, and stalk biomass percentages for the N application levels were not different from the control (Table 1). Stalk yield and diameter were affected by N application rates. Stalk yield tended to increase as N applications rates increased up to 168 kg N/ha, and at 224 kg N/ha, a significant reduction in stalk yield occurred compared to the 168 kg N/ha level. Thus, excess N application can be detrimental to stalk yield. Stalk diameter at 1 m was increased at the 112, 168, and 224 kg/ha N rates compared to the control (Table 1). Massey (1974) and Hovermale (1993) also reported that N significantly increased stalk diameter without increasing stalk yield.

Regressional analysis showed that the only consistent difference between the r values between rates was for the stalk biomass percentage (Table 2). As N application rates increased the correlation between stalk yields and stalk biomass percentages decreased (Table 2). At the 0 N rate, yields were significantly correlated, (r = 0.63) at P > 0.01 level, whereas at the 56 kg N/ha and 112 kg N/ha rate the positive correlation was at the P > 0.05 level. At the 168 kg N/ha and 224 kg N/ha rates there was no significant correlation between stalk yields and stalk biomass percentages.

Plant height, and stalk diameter were greater for 'Tainung 1' than 'Everglades 41', but no differences were detected between cultivars for plant population, stalk biomass percentage or stalk yield. 'Tainung 1' plants were 20 cm taller than 'Everglades 41' at 105 DAP and this trend continued until the final harvest when 'Tainung 1' was 23 cm taller than 'Everglades 41' (Table 1). The height advantage for 'Tainung 1' was achieve prior to 105 DAP and was maintained until the end of the growing season. These results were consistent with research in Missouri, Oklahoma, and Mississippi (Ching et al. 1993).

All yield components, except for plant population, were greater in 1989 than 1990 (Table 1). Plants in 1989 were 52 cm taller at 105 DAP, and 50 cm greater at harvest than in 1990. Stalk diameter was the only plant parameter significantly affected by N rates, cultivars and years, whereas stalk biomass percentage was only affected by years. Stalk yield was more than twice as great in 1989 (22.5 t/ha) than to 1990 (10.6 t/ha) (Table 1). Greater plant height, stalk diameter, stalk percentage and yield in 1989 may have resulted in part from an earlier planting date in 1989 (21 days) and greater early seasonal precipitation.


This research demonstrated that kenaf in loamy soils was relatively unresponsive to N application of 168 kg/ha and lower, and at high N-level there was a potential risk of decreasing stalk yield. Future research should examine the effect of other essential nutrients on fiber quantity and quality produced on specific soil types.


Table 1. Yield components of kenaf as influenced by nitrogen fertilization, cultivars, and years, means for 1989 and 1990.

Plant height(cm)
Variable Early Harvest Plant population (1000 plants/ha) Stalk diameters (mm) Stalk biomass (%) Stalk yield (t/ha)
Nitrogenz (kg/ha)
0 185 265 148 12.9 80.2 16.3
56 183 261 161 13.2 81.0 16.3
112 187 264 165 13.9 79.8 17.2
168 183 267 156 13.9 78.8 17.7
224 186 262 159 13.9 80.2 15.3
LSD (0.05)y NS NS NS 0.9 NS 2.0
Tainung 1 195 275 153 14.2 80.0 17.0
Ev. 41 175 252 163 13.0 80.0 16.2
LSD (0.05) 4 8 NS 0.6 NS NS
1989 211 289 152 15.2 83.3 22.5
1990 159 239 164 12.0 76.7 10.6
LSD (0.05) 4 8 NS 0.6 1.4 1.3
zNitrogen (kg/ha) means averaged across cultivars and years.
yLeast significant difference test level of P <0.05.
xCultivar means averaged across nitrogen rates and years.
wYear means averaged across nitrogen rates and cultivars.

Table 2. Coefficients of correlation (r) for yield components as related to stalk yield combined across cultivars and years.

Coefficients of correlation (r)
N (kg/ha) Plant ht. Plant population Stalk diam. Stalk (%)
Combined rates 0.74** -0.31** 0.75** 0.47**
0 0.81** -0.36 0.90** 0.63**
56 0.67** -0.24 0.59** 0.50*
112 0.71** -0.07 0.66** 0.56*
168 0.72** -0.63** 0.76** 0.43
224 0.81** -0.37 0.89** 0.46
*, ** Significant at 5% (*) or 1% (**) level.

Last update June 17, 1997 aw