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Francois, L.E., T.J. Donovan, and E.V. Maas. 1990. Salt tolerance of kenaf. p. 300-301. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.

Salt Tolerance of Kenaf

L.E. Francois, T.J. Donovan, and E.V. Maas

  1. INTRODUCTION
  2. METHODOLOGY
  3. SALINE INJURY AND PERFORMANCE
  4. CONCLUSIONS
  5. REFERENCES
  6. Table 1

INTRODUCTION

Kenaf (Hibiscus cannabinus L.) has long been recognized as a possible source of cellulosic fiber for pulp production in the United States (Ahlgren et al. 1950). With the introduction of this crop into the and southwestern states, plantings may be on soils where salinity problems already exist or may develop from the use of saline irrigation water. Preliminary studies to determine the effect of salt stress on germination and seedling growth of kenaf have been conducted using solution cultures in the greenhouse (Curtis and Lauchli 1985, 1986), but these studies provide no information on the effect of salinity beyond the seedling stage of growth. Since salt-tolerance data are not available to predict yield responses at later stages of growth, a field plot study was initiated to determine the effect of salinity on vegetative growth and yield of field-grown kenaf.

METHODOLOGY

This study was conducted at the Irrigated Desert Research Station, Brawley, CA. Two cultivars, '7818-RS10' and 'Everglade-41', were sown in 6.0 x 6.0 m plots on 26 March 1987. Each plot contained 5 rows of each cultivar. The rows were planted 0.5 m apart with the seed placed 50 mm apart within the row. The initial plant population was 400,000 plants/ha.

To assure a uniform stand across treatments, differential salination was not initiated until thirty days after planting when the plants were at the five-leaf stage of growth. Irrigation water salinities for each treatment were increased stepwise in two equal increments over a two-week period by adding equal weights of NaCl and CaCl2 until desired salt concentrations were achieved. The final electrical conductivities of the six irrigation waters (ECiw) were 1.4, 2.0,3.0, 4.0,5.0, and 6.0 dS/m. Approximately 65 mm of water were applied by flood irrigation to each plot every 7 to 10 days throughout the growing season.

Plants were harvested on 19 October 1987, 29 weeks after planting. Three meters of the middle 3 rows (4.5 m2) were harvested from the center of each half of each plot and fresh weights recorded. Ten plants were randomly subsampled from the harvested material, weighed, and measured for height. Leaves and side branches were removed and weighed separately from the stems. Samples were air-dried and percent dry matter determined. Stem diameter measurements were made 25 mm above the base of each plant. To determine the bast and woody fiber weight ratio, a 0.1-m section of stem was sampled 0.5 to 0.6 m above the stem base.

SALINE INJURY AND PERFORMANCE

The first injurious effect of salinity was noted approximately three months after salination was initiated, when the older leaves of '7818-RS-10' and `Everglade-41' from the 4.0, 5.0. and 6.0 dS/m plants developed tip and/or marginal necrosis. Although injury was slightly more severe on '7818-RS-10', the necrosis on both cultivars was correlated directly with the salinity level of the irrigation water.

Reduction in total yield and stem yield, associated with increasing levels of ECiw was nearly identical for the two cultivars (Table 1). Reduced plant height, stem diameter, and percent dry matter all contributed to the overall reduction in total vegetative growth and stem growth with increasing levels of salt stress.

The yield data for the two cultivars were combined and statistically analyzed with a piecewise linear response model (van Genuchten and Hoffman 1984). The data indicate that the tolerance threshold, i.e. the maximum allowable ECiw without a decline in yield, was 4.6 dS/m. Each unit increase in salinity above the threshold reduced yield by 36%.

According to the salt tolerance categories established by Maas and Hoffman (1977), kenaf would be classified as moderately tolerant to salinity. This classification agrees with the seedling tolerance reported by Curtis and Lauchli (1985).

Stem samples collected to determine bast to woody fiber weight ratios, which ranged from 1.8 to 2.0, showed no significant difference among salinity treatments.

CONCLUSIONS

Kenaf can be grown successfully with moderately saline irrigation water. However, salt levels in excess of 4.6 dS/m in the irrigation water will severely restrict plant growth and development and will result in a significant yield reduction. Irrigation waters currently used by most growers in the Southwestern United States contain salt levels less than 4.6 dS/m. However, poor irrigation water management with low salinity water can result in detrimental salt buildup in the soil profile, which will also restrict plant growth and development.

REFERENCES

Table 1. Total vegetative and stem growth of two Kenaf cultivars, '7818-RS-10' and 'Everglade-41', grown under six irrigation water salinities.

Total vegetative growth Stem growth
wt (kg/m2) wt (kg/m2)
Irrigation
water salinity
(ECiw) (dS/m)		 Fresh Dry Plant
height (m)		 Fresh Dry Dry
matter (%)		 Diameter
(mm)
'7818-RS-10'
1.4 6.13 1.28 2.96 3.80 0.84 22 25.3
2.0 7.17 1.63 3.12 4.42 1.02 23 26.9
3.0 7.64 1.52 2.89 4.53 0.97 21 24.7
4.0 6.85 1.34 2.63 3.53 0.76 21 25.5
5.0 6.30 1.15 2.27 3.34 0.65 19 24.0
6.0 3.75 0.66 1.84 2.17 0.40 18 22.3
Significancez
Linear *** *** *** *** *** *** *
Quadratic *** *** *** ** ** NS NS
'Everglade-41'
1.4 6.99 1.53 3.16 4.51 1.06 24 23.9
2.0 7.42 1.54 3.13 4.78 1.06 22 24.3
3.0 7.44 1.47 2.85 4.44 0.93 21 23.7
4.0 7.67 1.49 2.64 4.48 0.91 20 22.7
5.0 6.14 1.11 2.20 3.73 0.70 19 21.1
6.0 3.53 0.57 1.72 2.48 0.40 16 17.8
Significancez
Linear *** *** *** *** *** *** ***
Quadratic *** *** *** ** ** * **
zSingle degree of freedom comparisons
NS,*,**,*** Correlation nonsignificant (NS) or significant at 5% (*) 1% (**) or 0.5% (***).

Last update March 11, 1997 by aw