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Research Bulletin
Kenaf Production on a Saline Soil and Its Effect on the
Salinity of Soil and Shallow Aquifer, 1991
by
Mahendra S. Bhangoo, Fernando G. Fernandez
and Charles G. Cook
CATI Publication #930702
© Copyright July 1993, all rights reserved
ABSTRACT
Kenaf (Hibiscus cannabinus L.), was grown on a Nahrub clay saline
soil (Vertic Torriorthents) with a shallow water table to determine its
production potential and effect on the salinity of soil and shallow aquifer.
Three irrigation treatments, (0.6 m and 0.76 m or 24 and 30 inches), of
nonsaline water with ECiw of 0.7 dS/m and 0.76 m (30 inches) of saline water
with ECiw of 2.1 dS/m) were the main plots and eight kenaf varieties (
Everglades 71, C-108, Tainung 2, Guatemala 51, KK60, 45-9, 15-2, and an
Indian variety) were the subplots with four replications. Soil, plant
tissue, and the shallow aquifer water samples were taken for chemical
analysis.
Kenaf stem yields were the same for the two nonsaline water irrigation
treatments but were significantly higher (16 to 18%) than those for the
saline water irrigation treatment. Yield was negatively correlated with soil
salinity. The KK60 and the Indian varieties resulted in higher yield (12.8
and 11.7 Mg/ha or 5.7 and 5.2 tons /acre) than the other varieties. Leaf
yield as proportion of total dry matter yield was highest, 43.3 and 41.4%,
for the Indian and C-108 varieties and lowest for the KK60, G-51 and T-2.
Leaf yield per hectare was highest for the Indian and the kk60 varieties
(6.0 and 5.6 Mg/ha or 2.67 and 2.5 tons/acre) followed by the C-108 and 45-9
varieties. Bast fiber yield as proportion of total stem yield was highest
for the C-108, 45-9, G-51, and 15-2 varieties, respectively (40.0, 39.8,
39.5, and 39.2%). Bast fiber yield per hectare was highest (4.6 Mg/ha or 2.0
tons/acre) for the KK60 variety followed by the C-108 and Indian and 45-9
varieties. Accumulation of total salt, boron, and selenium by kenaf was
positively correlated with kenaf yield. Soil salinity up to 4.0 dS/m
appeared to be acceptable for kenaf production on saline soils irrigated
with 0.6 m of nonsaline water. Salinity of the soil and shallow aquifer in
the nonsaline irrigated plots decreased during the growing season.
The soils of the Westlands Water District located in the Central California
San Joaquin Valley (SJV) areas have salinity and a shallow water table
problem. The water table varies between 0.2 and 1.5 m (13). For these soils
to be productive, they must be drained to keep the water table below the
root zone. Drainage water high in salt, boron, and selenium, until very
recently, was disposed of in the Kesterson Reservoir and proved to be a
health hazard to the fish, and wildlife in the area due to accumulation of
salts, selenium, and other toxic minerals. At present, the Kesterson
Reservoir is closed and there is no outlet for the drainage water that is
accumulating in the soil and causing the water table to rise and soil
salinity to increase. If nothing is done to combat this problem, by the year
2000, 400,000 hectares (ha) or one million acres of land will become highly
saline and no longer suitable for crop production. This will result in
serious loss in crop production, farm income, and employment (13). Although,
soil salinity and shallow water table problems are acute on the west side of
the SJV, California, the results of this study will not only be important to
California but also to the other western states where irrigation is vital
for maintaining crop productivity on saline soils.
The solutions being sought to overcome this problem are both short-term and
long-term. A short-term, solution is the establishment of on site
evaporation ponds. The water in ponds evaporates, resulting in high
concentrations of salts, selenium, and other toxic ions. In addition, there
is a possibility of leaching this concentrate into the underground water and
causing it to become high in salts, boron, and selenium. Furthermore, the
ponds take about ten to twenty percent of land out of production. One
long-term solution sought is to grow salt-tolerant trees such as Eucalyptus
and Casuarina species. Another crop under study is Atriplex canescens (8).
An alternative ameliorative practice would be to grow a multipurpose annual
crop that can tolerate the existing soil conditions and that can reduce
drainage water disposal volume.
Growing a multipurpose crop, such as kenaf, that is moderately salt
tolerant, can meet part of its water requirements by uptake from the shallow
water table, remove substantial quantities of salts including boron and
selenium from the soil, appears to be an economically viable method of
ameliorating the problem and lowering the boron, seleniun content and
salinity of soil and the shallow aquifer.
Kenaf (Hibiscus cannabinus L.), an annual crop, is a source of fiber
that can be used for making high quality paper and other related products
and cattle feed (3,5,9,12). It can be grown in the San Joaquin Valley as a
cash crop (1). It is known to be moderately salt tolerant and can be grown
on any soil type including saline soils (1,2,4,5,6,10). Curtis and Lauchli
(4) reported a kenaf seedling yield decrease of 20 to 40 and 70 to 80% by 75
and 150 mmoles of NaCl, respectively in the growth medium. According to
Francois et al. (6) kenaf grown on saline soil irrigated with saline water
showed 11.6% yield decrease for each unit increase in soil salinity above
8.1 dS/m. These results place kenaf in a salt tolerant category. Robinson
(10) reported that kenaf can be grown in the Imperial Valley, California on
saline soils when 1.3 to 1.4 m of good quality water is used for irrigation.
Use of saline water for irrigation of kenaf resulted in a 80 to 90%
reduction in yield. Bhangoo and Fernandez (2) during 1990 found total dry
matter and stem yield of the Indian, Guatemala 51, Everglades 41 and 71
kenaf varieties to decrease substantially with soil salinity greater than
5.5 dS/m. These workers found kenaf to be effective in removing substantial
amounts of salt, boron, and selenium from soil if total biomass was removed
from the field. Kenaf grown on a saline soil with a shallow aquifer required
only 0.76 m or 30 inches of irrigation water. Muchow and Wood (11) reported
that kenaf grown in a semi-arid tropical environment can use as much as 1.2
-1.4 m of water. This indicates that kenaf can be grown with less water on
soils with shallow water table than on soils without shallow water table as
is the case with cotton and alfalfa (7).
The objectives of this study were to (i) determine production potential of
kenaf grown on a saline soil irrigated with nonsaline and saline water (ii)
evaluate 8 kenaf varieties for their stem, leaf, and bast fiber yield (iii)
measure salt removal by kenaf varieties from soil and its effect on the
salinity of soil and the shallow aquifer.
MATERIALS AND METHODS
The experimental plots were located at the Northeast corner of Adams and
Derrick avenues (36° 47' N, 120° 53' N) in the Westlands Water District
near Tranquillity, California. The soil type was a saline Nahrub clay (fine,
montmorillonitic, thermic, Vertic Torriorthents) with inclusions of Cuervo
clay. The salinity level of these soils ranges between 3-5 dS/m. The
effective root depth of crops grown in the area is limited by a perched
water table (shallow aquifer) that generally lies at a depth of 0.9 to 1.2
m. Eight varieties of kenaf, Everglades (E) 71, C-108, Tainung (T) 2,
Guatemala (G) 51, KK60, 45-9, 15-2, and an Indian variety were planted on 2
May 1991. Three irrigation treatments (0.60 and 0.76 m or 24 and 30 inches
of nonsaline water with ECiw = 0.7 dS/m) and 0.76 m of saline water (EC of
2.1 dS/m) were the main plots and the kenaf varieties were the subplots with
four replications. Kenaf seed was planted on one m wide rows. Plot size
consisted of six rows 30 m or 98 ft. long. Seed germination, regardless of
the salinity of soil and irrigation water salinity, was excellent for each
variety. Plant density resulted in about 350,000 plants/ha or 140,000
plants/acre. Nitrogen, as urea ammonium nitrate, at the rate of 140 kg N/ha
or 120 lb/acre was applied in two split applications.
Four observation wells, 2.5 m or 8.2 ft. deep , were installed on 2 June
1991 for measuring water table level and getting water samples for chemical
analysis before and after each irrigation. Soil and plant tissue samples
were taken on 17 July and 18 October 1991 for chemical analysis. Soil
samples were taken to a depth of 30 cm or 12 inches of soil from each
subplot for salinity determination. Plants were harvested on 18 October from
each subplot from middle two rows 10 m or 33 ft. long for stem yield. Bast
fiber yield was determined at harvest time from middle one meter portion of
ten stems per subplot. Leaf yield included the leaves on the stem and the
leaves that had abscissed and accumulated (1 m2
or 3.28 ft2area) on the ground.
Plant samples( stem and leaf) were taken from each subplot and chemically
analysed for total N (Kjeldahl method), P (Bray's method), Ca, Mg, K, and Na
(atomic absorption-emission spectrophotometer), Cl (chloride titrator
method), S (turbidimetric) method),. Micronutrients ( Fe, Mn, Zn, Cu) were
determined by using wet digestion method and atomic absorption
spectrophotometer. Boron was determined with the azomethine colorimetric
method. Soil and water salinity was determined by means of Electrical
Conductivty method. Total salt removal by kenaf was calculated based on
concentration each element and yield of foliage and stems of each variety.
Soil, plant, and water analysis and plant yield data were subjected to
analysis of variance as dictated by the experimental design.
RESULTS AND DISCUSSION
Stem Yield and Height
Stem yield, from plots irrigated with nonsaline water, was significantly
higher than those irrigated with saline water (Table 1). Since there was no
difference in stem yield between the 0.61 and 0.76 m of nonsaline water
irrigation treatments, these yield data were combined for statistical
analysis. Stem yields of different kenaf varieties from plots irrigated with
the nonsaline and saline water varied from 8.1 to 12.8 (3.6 and 5.7
tons/acre) and 5.9 to 10.7 Mg /ha (3.61and 4.8 tons/acre), respectively and
were negatively correlated with soil salinity (Fig.1 and 2). The KK60 and
the Indian varieties resulted in highest stem yield whereas the G-51, E-71,
and the 15-2 were the lowest in yield. Stem yield from plots irrigated with
the saline water was 16 to 18% lower than that from plots irrigated with the
nonsaline water. Stem height (Table 1) of the different varieties from plots
irrigated with nonsaline water was higher than those irrigated with saline
water and varied from 261 to 296 and 239 to 280 cm (8.56 to 9.87 ft. and 8.0
to 9.3 ft.), respectively. The KK60, 45-9, and T- 2 were taller than the
other varieties. The Indian variety had the shortest stems. With the
exception of the Indian variety, stem height of other kenaf varieties was
positively correlated (R2= 0.707) with stem yield. The Indian variety,
despite its low height produced a high stem yield because it branched more
than the other varieties grown in a wide row spacing such as the one used
for this study.
 
Leaf and Bast Fiber yield
Leaf yield as a proportion of total dry matter (%) was not significantly
different between plots irrigated with nonsaline and saline water ( Table
2). However, different varieties produced significantly different proportion
of leaf yield. Leaf yield of different varieties ranged between 36.0% for
the KK60 and 43.3% for the Indian varieties. The Indian, C-108, and 45-9
varieties produced highest leaf percentage whereas the G-51, KK60, T-2,
produced the lowest leaf percentage. Dry leaf yield (DLY) in Mg/ha was
significantly higher in plots irrigated with nonsaline water than those
irrigated with saline water (Table 2). Plots irrigated with nonsaline water
resulted in highest DLY for the Indian and KK60 varieties (6.0 and 5.6 Mg/ha
or 2.67 and 2.5 tons/acre). The G-51 and 15-2 varieties produced the lowest
DLY. Plots irrigated with saline water showed a similar trend, however, the
DLY was about 13% lower than those irrigated with nonsaline water.
Bast fiber yield (BFY), proportion of dry stem tissue (%) of different
varieties, was not significantly different between the irrigation tretments,
however, it was significantly different among varieties. It ranged between
35% and 40% for the T-2 and the C-108 varieties, respectively. The C-108,
45-9, G-51, E-71, and15-2 varieties produced the highest whereas the Indian
variety produced the lowest BFY. Bast fiber yield (Mg/ha) in plots irrigated
with nonsaline water was higher than those irrigated with saline water
(Table 2). In addition, there were significant differences in fiber yield
among varieties in irrigation treatments. In plots irrigated with nonsaline
water, the KK60 variety produced highest BFY (4.6 Mg/ha or 2.0 tons/acre)
followed by the C- 108, Indian, and 45-9 varieties. In plots irrigated with
saline water similar trend was observed, however, the yield was 21% lower
than those irrigated with nonsaline water. The leaf and bast fiber yield was
positively correlated with the stem yield (R2 = 0.837 and 0.753) regardless
of the irrigation water quality.
Salt, Boron, and Selenium Uptake and Protein Yield
Salt uptake by different varieties in stems and leaves from the plots
irrigated with nonsaline and saline water varied from 730 to 1,233 and 570
to 923 kg/ha (651 to 1100 and 509 to 824 lb/acre), respectively. The amount
of boron uptake in the stems was very low whereas in the leaves it was high.
The amount of total boron uptake in the above ground whole plants ranged
between 134 and 218 kg/ha (120 and 195 lb/acre). The KK60 and the Indian
varieties removed highest amount of boron. Manganese and zinc uptake was
highest for the KK60 and C-108 varieties. The amount of selenium uptake by
the C-108, KK60, T-2, and E-71 was higher in the stems than in the leaves
with the exception of the Indian variety that contained more selenium in the
leaves. Selenium removal in the total dry matter varied from 1.11 to 2.9
kg/ha (1.0 to 2.59 lb/acre). The C-108 and the Indian varieties were the
highest removers of selenium from soil.
Total salt uptake in total biomass was highest (2,156 kg/ha or 1925 lb/acre)
for the KK60 variety followed by the Indian, 45-9, and C-108 varieties
(Table 3). Total salt uptake (Fig.3) was positively correlated with the
total dry matter yield (R2= 0.875). This indicates that kenaf can remove
substantial amounts of salt, boron, and selenium from soil. By virtue of its
salt removal capacity, kenaf can be effective in reclaiming saline soils if
all the biomass is removed from the field. Protein yield for the KK60 and
Indian varieties amounted to 3,420 and 3,509 kg/ha (3053 and 3133 lb/acre),
respectively (Table 4). High protein, salt, and selenium yield of kenaf
makes it suitable for livestock feed. The only way the total biomass can be
removed from the field if kenaf is used as livestock feed.
Water Table Level and Salinity of Water and Soil
The water table level (Table 5) on 10 June 1991 was 0.64 m (25 in ) and
showed a fluctuation of about 0.6 m (24 in) in the interval between
irrigations during the active kenaf growing season. Later in the season, the
fluctuation of water table was about 0.2 to 0.3 m (8 to 12 in) . On October
19, at harvest time, the water table level was greater than 2.1 m (6.9 ft)
and there was no standing water at this depth. There was no difference in
the water table level in the plots where 0.60 and 0.76 m (24 and 30 in) of
irrigation water was applied. Average salinity level of the shallow aquifer
on 10 June 1991 was 7.9 dS/m. During mid October, in the plots irrigated
with nonsaline water, it decreased to 5.5 dS/m and in the plots irrigated
with saline water, it increased to 9.6 dS/m (Fig. 4).
Soil salinity (Table 6) in the plots irrigated with nonsaline water in July
was 4.3 dS/m and decreased to 3.2 dS/m by mid-October whereas in the plots
irrigated with saline water it increased from 3.6 to 4.2 dS/m. This
indicates that continued irrigation with saline water (2.1 dS/m) will
eventually salinize the soils to the point that they will become
unproductive. Studies conducted by the authors during 1990 and 1991 show
that kenaf grown on a saline soil with shallow aquifer required only 0.60 m
of good quality irrigation water. Since kenaf irrigated with 0.6 and 0.76 m
of nonsaline water produced the same yield and used water from the shallow
aquifer, it appears that kenaf grown on a saline soil can probably help
reclaim saline soils and possibly lower or maintain the water table level
where irrigated agriculture is practiced.
CONCLUSIONS
Results of this study indicate that kenaf can be grown, with 0.6 m (24 in)
of nonsaline irrigation water, on saline soils in which the salinity level
does not exceed 4.0 dS/m provided that the irrigation water is of good
quality (ECiw <1 dS/m). The soils with salinity levels greater than 4.0
dS/m do not appear to be conducive for kenaf production even when irrigated
with good quality water. Irrigation of kenaf with saline water on saline
soils will cause the soils to become saline and will severely reduce kenaf
growth and yield. The KK60 and the Indian varieties were the highest
yielders, whereas the G-51, E-71, and 15-2 varieties were the lowest
yielders. With its salt removal capacity, kenaf can lower soil salinity and
make it more suitable for crop production. Production of kenaf on saline
soils is feasible when planted to salt tolerant varieties. Further research
is underway to evaluate more varieties for their salt tolerance. feasible if
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