Growth and yields of kenaf varieties in central Greece
E. Alexopoulou *, M. Christou, M. Mardikis, A. Chatziathanassiou
Center for Renewable Energy Sources,19th km Marathonos A6e.,19009,Pikermi,Attiki,Greece
Accepted 8 October 1999
Abstract
Kenaf is a rapidly growing crop of great interest as a source of low cost natural fiber. Kenaf fibers can be used in the manufacture for a wide range of pulp, paper and paperboard products and may be a substitute for fiberglass and other synthetic fibers. The purpose of this work was to study the adaptability, growth and yields of three early (PI 3234923, PI 318723 and PI 248901) and four late-maturity kenaf varieties (Everglades 41, Everglades 71, Tainung 2 and JT1) in central Greece. In a period of 3 years (1994, 1995 and 1997), three kenaf field trials were conducted in two fertile sites (Kopais and Aliartos) in central Greece. In the first experiment (1994), the density of the trial was 240 000 plants/ha, while in the second (1995) two plant populations were tested (320 000 and 170 000 plants/ha). Due to the fact that in 1995 the higher plant population (320 000 plants/ha) resulted in higher yields, the following trial of 1997 was decided to be designed only for the high plant density. Data collected in all experimental fields included canopy height, leaf area index (LAI), basal stem diameter, fresh and dry yields and yields components. In contrast with the early-maturity varieties, the late-maturity ones resulted in higher values for all the tested parameters. In all trials, this superiority was statistically significant (LSD Test,P=0.05) from early August until the end of the growing period. Early varieties exhibited 33.34 t/ha fresh biomass yields (PI 248901, 1997) and late varieties 88.66 t/ha (Tainung 2, 1994). The corresponding values for dry matter yields varied from 9.40 t/ha (PI 318723, 1997) to 23.95 t/ha (Tainung 2, 1994). Between the two plant populations, the high (320 000 plants/ha) was more productive than the low one (170 000 plants/ha), but this difference was statistically significant only until the flowering phase. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Adaptability; Growth; Late and early-maturity kenaf varieties; Yield; Yield components
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1. Introduction
Kenaf (Hibiscus cannabinus L.) is a rapidly growing crop of great interest as a source of low cost natural fiber and feedstock for energy
pro-duction as well. Kenaf fibers can be used in the manufacture for a wide range of pulp, paper and paperboard products and may be a substitute for fiberglass and other synthetic fibers. As fibrous crop, kenaf appears to have enormous potential to become a valuable biomass crop of the future. When it is cultivated in high plant population, it has an erect stem consisting of an inner core of short woody fibres 0.5 – 1 mm long and an exter-* Corresponding author. Tel.:+30-1-6039900; fax: +
30-1-6038006.
E-mail address:ealex@cres.gr (E. Alexopoulou)
E.Alexopoulou et al./Industrial Crops and Products11 (2000) 163 – 172 164
Table 1
Site coordinates of the field trials
Site Kopais Aliartos
number of kenaf varieties (early and late) in two fertile sites of central Greece. The tested varieties have been selected for their high yielding potential in relative trials worldwide.
2. Material and methods
2.1. Experimental sites
In a period of three years (1994, 1995 and 1997) three kenaf experimental fields were established in two fertile sites (Kopais and Aliartos) in central Greece. In the first and second year, the experi-ments were conducted in Kopais and in the third year in Aliartos.
Kopais is located in a large plain of about 20 ha, derived from the drainage of lake Kopais. Kopais field is characterized by a very fertile soil with high percentage of organic matter (Table 2). Due to a high underground water table from late spring to early summer, soil moisture content approached saturation level during the early growth stage.
Aliartos (Forest Service Nursery of Aliartos) is situated 7 km away from the Kopais field. It should be noted that Aliartos field was located at the bank of lake Kopais. Although the two sites were located in short distance (Table 1), the soil texture was greatly differentiated (Table 2).
In Kopais field, the previous crops were cereals and corn that were cultivated in rotation for a number of years. On the contrary, Aliartos was left fallow from 1978.
The climate in both sites is characterized as continental with large temperature variations be-nal bark with fibres 3 – 4 mm long. The bark fibres
are comparable to soft woody fibres, while the inner short, woody fibres of the core are compara-ble to hardwood fibres (Francois et al., 1992). The paper produced from paper pulp has excellent ink-retention characteristics and its high tensile strength is ideal for high-speed presses (Robinson, 1988).
Flowering of late-maturity kenaf varieties is under photoperiodic control and plants remain vegetative until daylight falls below 12 h and 45 min. On the contrary, photoperiodic does not influence the flowering of the early-maturity kenaf varieties.
A great number of varieties (late and early) have been tested under various environments and cultivation methods worldwide. It is reported that most of the late-maturity varieties resulted in higher yields compared to the early ones (Petrini et al., 1994).
High plant populations have been reported to exhibit higher fresh and dry matter yields (Higgins and White, 1970; White et al., 1971; Muchow, 1979; Bhangoo et al., 1986; Kipriotis et al., 1998). Due to the limited information referring to kenaf cultivation in Greece, this work aimed at testing the adaptability, growth and yields for a
Table 2
Soil characteristics of the field trials
Site Kopais Aliartos
Soil layers 0-40 cm humic layer, 40–80 cm marl, 0–58 cm SC, 58–82 cm CL, 82–92 cm S, 92–110 cm S, 110+cm S
80+cm sand
0.536a
Organic matter (%) 4.5a
95.30a
Electrical conductivity 39.19a
(mmhos/cm)
PH 7.98a 8.00a
Fig. 1. Monthly max and min air temperatures for the years 1994, 1995 and 1997.
Fig. 2. Monthly rainfall for the years 1994, 1995 and 1997.
tween day and night and strong winds. The high air temperatures that occurred in the experimental sites from late May to late September in relation to the low rainfalls made irrigation necessary for covering the crop needs (Figs. 1 and 2).
Irrigation was applied by the drip method and the pipes of the drip system were also used for nitrogen fertilization.
2.2. Experimental layouts
late-matu-E.Alexopoulou et al./Industrial Crops and Products11 (2000) 163 – 172 166
rity varieties. The density of the trial was 240 000 plants/ha. In the course of the growing period, the plants received 333 mm of water in total, except for the rainfalls. When the plants were 40 cm high, a quantity of 75 Kg N/ha was applied through the drip irrigation system.
In the following year, a more complicated trial was carried out next to the previous one (Table 3). Based on the results obtained from the previ-ous trial, it was decided plant population to be studied as a factor in addition to variety. On May 31, 1995, three early varieties (PI 3234923, PI 248901 and PI 318723) and two late (Everglades 71 and JT1) were sown in two plant populations (320 000 and 170 000 plants/ha) (Table 3). Except for the rainfalls, 329 mm of water was applied from late May to late September. At the early stages of growth, nitrogen fertilization (50 Kg N/ha) was applied through the drip irrigation system.
A third experimental field was conducted in 1997 at Aliartos and five varieties (PI 3234923, PI 248901, Everglades 41, Everglades 71 and Tain-ung 2) were sown on June 2 (Table 3). The first two were early and the latter three were late-ma-turity varieties. Based on the high yields that were
recorded in 1995, in the plots with the
higher plant population (320 000 plants/ha), the same high plant population decided to be used only in this trial. All plots received 355 mm of water and 75 Kg N/ha of nitrogen fertilization. The experimental layouts, the under study factors as well as the plot size for all trials are presented in Table 3. Trials were kept weed free by hand hoeing.
2.3. Measurements
In the course of each field trial, canopy height was regularly measured and growth rate was estimated.
In order to estimate fresh and dry yields and yields components several harvests were carried out during all years. Harvests started in late July and continued until the end of December. In each harvest date a one-meter row (0.7 m2) was har-vested and the leaves were separated from the stems. Sub-samples from each fraction were taken for LAI and dry matter determination. Leaf area was calculated with a Leaf Area Meter. Dry mat-ter in stems and leaves was evaluated afmat-ter drying the samples at 85°C at constant weight. More-over, a harvest of a larger area (8.4 m2
) was accomplished from late October to early Novem-ber in each site. At that time the early varieties were at the stage of seed maturity, while the late varieties were at the end of the flowering phase. Because of the quite high moisture content at that time, a couple of harvests were accomplished later in the season until the end of the year, in order to estimate the most appropriate harvesting time for energy purposes.
Basal stem diameter was measured in each trial at the end of the growing season. At the end of the growing season in the 1994 field trial, bark was separated from the core and fresh and dry stem components (bark and core) were estimated on fresh and dry matter basis and bark/core ratio as well.
The effect of the tested varieties on yields was
tested by a standard analysis of variance
(ANOVA). The effect of variety, plant population
Table 3
Experimental layouts and factors of the field trials
Treatments
Year Experimental layout Plot sizea
Randomized complete block in PI 3234923, Everglades 41, Everglades 71, 6×4.5 m2, 20 plots,
1994
Tainung 2, JT1
three replications (6 rows per plot)
PI 3234923, PI 248901, PI 318723, Ever- 6×4.5 m, 20 plots, 1995 A randomized complete block factorial 22in
(6 rows per plot) glades 71, JT1, 320 000 pl/ha, 170 000 pl/ha
two replications
Randomized complete block in 6×5 m, 15 plots,
1997 PI 3234923, PI 248901, Everglades 41,
Ever-(7 rows per plot) three replications glades 71, Tainung 2
Table 4
Growth characteristics for all the tested parameters in all field trials
Basal Stem Diameter (mm)
Factors Final Canopy height (cm) Maximum Leaf Area Index (LAI)
Kopais,1994 Varieties
271.20a*
PI 3234923 12.00a 3.08
357.47b
Everglades 41 15.50b 4.54
15.25b
302.87b 4.37
Everglades 71
Tainung 2 359.95b 16.00b 3.83
15.50b 4.05
PI 248901 14.32a 1.92
13.64b
170 000 plants/ha 17.84b 1.76
Aliartos,1997 Varieties
PI 248901 277.70a 13.13a 3.07
12.96a
266.60a 3.12
PI 318723
14.90b
Everglades 41 314.90a 3.99
15.30b
314.40a 4.23
Everglades 71
15.23b 3.87
Tainung 2 293.80a
and their interaction on yields and yield compo-nents in the field trial of 1997 were also analyzed as mentioned before. LSD multiple range tests were used in partitioning the means (statistical significance at theP=0.05). The STATGRAPH-ICS statistical software was used in carrying out the data analysis.
3. Results and discussion
3.1. Growth characteristics
Growth rate was rather high for all varieties until the flowering phase (up to 4.38 cm/day) and thereafter it was gradually decreased. It is re-ported (Petrini et al., 1994) that kenaf has an indeterminate type of growth with rapid growth rate increases until the appearance of the first flowers and gradual decreases afterwards.
In all trials, early-maturity varieties (PI 3234923, PI 248901 and PI 318723) were shorter than the late ones (Everglades 41, Everglades 71, Tainung 2 and JT1). The early-maturity varieties grew 267 cm tall, averaged over the years and sites. Correspondingly, the late-maturity varieties reached a mean height of 330 cm. In the first and the second trial this superiority was statistically significant (Table 4). More specifically, final canopy height of the early varieties varied from 256 cm (PI 318723, 1995) to 277.7 cm (PI 248901, 1997) and the late ones from 298.80 cm (Tainung 2, 1997) to 369.97 cm (JT1, 1994). Plant popula-tion did not significantly influence the canopy height, though a certain superiority of the low plant density was highlighted (Table 4).
E.Alexopoulou et al./Industrial Crops and Products11 (2000) 163 – 172 168
stem diameter recorded in the low-density plots was significantly higher (17.84 mm) compared with the high-density plots (15.15 mm).
Leaf area index (LAI) of all the tested varieties reached maximum values on different dates, de-pending on their maturity type. Early varieties reached the highest values for LAI around 215 Julian date, while the late ones gave the peak values 35 – 40 days later. In Table 4, only the maximum values are presented, irrespective of the sampling date, therefore statistically significant differences could not be traced. However, it can be seen that the mean max LAI of the early varieties, averaged over the years and sites, was considerably low, 2.56 compared to 3.95 that was recorded for the late-maturity varieties. Regarding the max LAI for each plant density, presented in Table 4, it refers to 251 Julian day and it is averaged over all the tested varieties of the trial. According to the table, denser plantations re-sulted in higher maximum LAI values.
3.2. Yields
Fresh and dry matter accumulation, as pre-sented in Fig. 3, varied considerably according to the maturity type of kenaf varieties, while site effect was rather negligible. More specifically, fresh and dry matter accumulation for all the tested varieties (early and late) was similar until 240 Julian day, when the early varieties bloomed. Thereafter, yield accumulation of the early vari-eties was gradually declined until the end of the growing period. In contrast with the early vari-eties, fresh and dry matter yield accumulation for the late ones exhibited a rapid increase until the 300 Julian day, when the peak values were recorded, that is 60 days later that the early varieties. Thereafter, yields were sharply declined due to the defoliation of the plants and the de-crease of the biomass moisture content (Fig. 3).
It should be pointed out that fresh and dry matter yield components in all trials were found to vary considerably from August to the end of the growing period, according to the maturity type of the tested varieties. In all trials the varia-tion was statistically significant (LSD test, P=
0.05) (Table 5).
It can be seen that, in general, late varieties were more productive than the early ones. Maxi-mum yields of 44.39 and 73.7 t/ha fresh matter were recorded for the early and late-maturity varieties, respectively, averaged over the years and sites. Correspondingly, mean dry matter yields were 10.14 and 18.99 t/ha. As previously men-tioned, the maximum yields of the early varieties refer to 240 Julian day, while the maximum yields of the late varieties refer to the 300 Julian day. Late kenaf varieties achieved higher yields due to the fact that they remained vegetative two months more than the early ones. As reported (Petrini et al., 1994) there is a positive relation between kenaf productivity and absence of the flowering phase.
Each year, the peak values for fresh and dry matter yields were recorded from late October until early November (Fig. 3). At that time the harvest was carried out in a larger area (8.4 m2) compared to the other harvests (0.7 m2), in order to assure more realistic estimations. Means for fresh and dry matter yields and yield components, at this harvest are presented in Table 5. Early varieties produced fresh biomass yields that ranged from 24.64 t/ha (PI 3234923, 1994) to 33.34 t/ha (PI 238901, 1997), while the dry matter yields ranged from 6.27 t/ha (PI 3234923, 1995) to 9.40 t/ha (PI 318723, 1997). Correspondingly, late varieties resulted in fresh yields that varied from 52.78 t/ha (Everglades 71, 1995) to 88.66 t/ha (Tainung 2, 1994) and dry matter yields from 13.32 t/ha (Everglades 71, 1995) to 23.95 t/ha (Tainung 2, 1994).
E.Alexopoulou et al./Industrial Crops and Products11 (2000) 163 – 172 170
Table 5
Means of the yields and yield components (LSD test,P=0.05) for all the tested parameters in all field trials
Factors FBYa (t/ha) DMYb(t/ha) FSYc(t/ha) DSYd(t/ha) FLYe(t/ha) DLYf(t/ha)
Kopais, 1994 (Julian day, 315)
Varieties
7.07a 24.60a 7.09a
24.64ag 0.00a
PI 3234923 0.00a
19.75b 66.40b 18.10b
Everglades 41 74.42b 8.00ab 1.59b
20.43b 72.10b 17.30b
87.36b 15.20c
Everglades 71 0.07c
23.95b
Tainung 2 88.66b 78.50b 21.70b 10.10bc 2.19bc
21.90b 70.00b 20.10b
78.57b 8.50abc
JT1 1.93bc
Kopais, 1995 (Julian day, 299)
Varieties
6.27a 23.57a 5.82a 2.05a 0.45a
PI 3234923 25.62a
6.60a 24.46a 6.03a
26.60a 2.14a
PI 248901 0.57a
6.24a 23.39a 5.64a
PI 318723 25.77a 2.24a 0.60a
13.32b 40.71b 11.44b
52.78b 12.07b
Everglades 71 1.88b
JT1 60.93b 16.39b 47.50b 13.48b 17.00b 2.90b
Populations
9.82a
320 000 plants/ha 38.90a 32.71a 8.49a 7.67a 0.96a
37.20a
170 000 plants/ha 9.71a 31.14a 8.48a 6.53a 1.60a
Aliartos, 1997 (Julian day, 298)
Varieties
9.18a 24.76a 7.31a
33.34a 8.57a
PI 248901 2.08a
9.40a 25.24a 6.71a
PI 318723 33.32a 8.09a 2.47a
16.53b 49.52b 12.42b
72.38bc 22.85c
Everglades 41 4.11b
79.52c
Everglades 71 20.73c 55.24b 15.84c 24.28c 4.89c
17.92bc 50.00b 14.16bc 18.57b 3.76b
68.57b Tainung 2
aFBY, fresh biomass yields. bDMY, dry matter yields. cFSY, fresh stem yields. dDSY, dry stem yields. eFLY, fresh leaf yields. fDLY, dry leaf yields.
gMeand followed by the same letter do not differ significantly (PB0.05, LSD test).
concerned, was still recorded, though it was not statistically significant.
Among the trials, in 1995 fresh and dry matter yields and yield components were lower compared to the other two trials, as far as Everglades 41 and JT1 are concerned. These lower yields could be related to the lower nitrogen fertilization rate (34%) that was applied that year.
At the end of the season, in the first field (Kopais, 1994), bark and core were separated and fresh and dry matter yields for each fraction along with the bark to core ratio were assessed. The relative data are presented in Tables 6 and 7.
4. Conclusions
Table 6
Means of stem yields and stem components (core and bark) on a fresh and dry basis
DSY2 FBY3 DBY4 FCY5 DCY6
Variety FSY1a
9.06a 5.33a
PI 3234923 17.36ab 2.64a 12.03a 6.42a
Everglades 41 36.11ab 11.68a 8.63ab 3.61ab 27.48b 8.07a
13.13a 9.41ab 5.46b 28.63b
Everglades 71 38.04b 8.57a
14.04a 10.56b 4.34ab
48.40b 37.84b
Tainung 2 9.70a
10.89a
JT1 40.38b 9.82b 3.94ab 30.56b 6.95a
aFSY1, fresh stem yields; DSY2; dry stem yields; FBY3, fresh bark yields; and DBY4, dry bark yields; FCY5, fresh core yields;
and DCY6, dry core yields
bMeans followed by the same letter do not differ significantly (PB0.05, LSD Test).
Table 7
Mean percentage of bark, mean percentage of core and bark:core ratio on a fresh and dry basis
Variety Fresh basis Dry basis
Bark (%) Core (%) Bark:core ratio Bark (%) Core (%) Bark:core ratio
PI 3234923 30.70 69.29 0.44 29.14 70.68 0.41
76.10 0.31 30.91
23.90 69.09
Everglades 41 0.44
24.74
Everglades 71 75.26 0.33 34.73 65.27 0.53
78.18 0.28 30.91 69.09
Tainung 2 21.82 0.45
75.68 0.32 36.18 63.82
24.32 0.57
JT1
ones (PI 3234923, PI 248901 and PI 318723). Consequently, in the climatic conditions of central Greece and in fertile and well-watered soils, the late maturity varieties can be considered as the most appropriate to be grown.
High plant population (320 000 plants/ha) re-sulted in shorter and thinner plants, though this superiority was not significant. Nevertheless, as far as fresh and dry matter yields are concerned a certain but not significant superiority of the high plant density over the low one was recorded at the final harvest. It has been found that doubling plant population may increase final fresh and dry matter yields by as little as 4.5 and 1.1%, respectively.
Harvesting time ranges from the end of October to December depending on the final end-use (fiber or energy production). At the end of October, when fibers of the highest quality could be ob-tained, the late-maturity varieties exhibited the highest biomass yields. However, the high mois-ture content of the harvested material is pro-hibitive for energy production. Soon after a killing
frost (end of November) the plants defoliated and the moisture content decreased, to the benefit of the energy exploitation of the harvested material. A further postponement in the harvesting time (December) lead to a further decline in moisture content, but also caused additional dry matter losses, due to the losses of leaves and stems.
Seed production was always feasible for the early varieties, while for the late ones seed produc-tion depended on the prevailing climatic condi-tions during autumn.
Additional studies are needed to determine the most appropriate varieties for Greece as well as the cultural practices leading to the maximization of the yields (irrigation, fertilization rates and plant density).
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