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Effect of chemical and organic fertilizers on growth and yield of two roselle (Hibiscus sabdariffa L.) cultivars

Chemical and organic fertilizers are limit factors of crops growth. A field experiment was conducted for two consecutive summer seasons (2011 and 2012) at the Demonstration Farm of the Faculty of Agriculture, Omdurman Islamic University (Fitaihab). The objective of the study was to investigate on the effect of chemical and organic fertilizers on growth and yield of roselle (Hibiscus sabdariffa L.). Two varieties namely Bulk (V1 – local) and Omshiback (V2- improved) were used to assess their performance in respect to application of chemical and organic fertilizers. Chemical fertilizer involved 0, 40, 80 kg N/fed and 40 N + 40 kg P2O5/fed, whereas fermented organic fertilizers were 2 ton chicken manure/fed and 3 ton cattle manure/fed. The experiment was designed in a split-plot design with four replications. The findings of the study reveal that, among the two varieties, there were no significant differences between them for all studied parameters (plant height, number of nodes/plant, number of leaves/plant, leaf area, number branches/plant, plant dry weight and yield of dry calyces), except number of nodes/plant during the 1st season, when V1 significantly exceeded V2 for this parameter. Meanwhile, application of chemical and organic fertilizers significantly affected only number of leaves/plant only during the 1st season, when both F1 and F2 treatments obtained the significantly higher mean of this parameter as compared to the other treatments.


Introduction
Roselle (Hibiscus sabdariffa L) is a member of the family of Malvaceae. Roselle is an ornamental and medicinal plant or annual herb but provides limited annual plants in some environments, which are essential yearly plants that are successfully grown in tropical and sub-tropical regions [1,2]. Throughout Roselle growing regions, the crop is grown traditionally without application of chemical or organic fertilization, although it reacts favorably to these fertilizers when researched, by growing more vigorously.
Van Damme and Viaene [3] stated that for vigorous growth, regular supply of plant nutrients, especially the macro elements is necessary. Enwezor et al. [4] mentioned that the soils of savanna zone are predominantly coarse-textured and characteristically low in organic matter and hence are potentially low in natural fertility and therefore cannot sustain high crop yield under continuous cultivation without application of fertilizers. Duke and Aychely [5] mentioned that roselle plants responded favorably to nitrogen fertilizer. Adamson et al. [6], Rhoden and Small [7], Rhoden et al. [8] and Atta et al. [9] stated that for high yield of calyces, high rate of nitrogenous fertilizer is needed, but  [10].
The growth rate of Roselle was increased as level of nitrogen increased [11]. Gibson and Waring [12] found that yield of Roselle was increased when the crop followed legume crops. Hago and Oman [13] observed that the growth and yield of roselle were significantly affected by application of both nitrogen and phosphorus, but phosphorus had less effect on growth of Roselle than nitrogen. Similar results were also reported by Abdelbagi [14]. Abu Elseoud et al. [15] stated that application of compost to newly reclaimed soils significantly increased both the dry matter and yield of fruits for the cultivated roselle. Gad [16] observed that the application of both chicken and cattle manure significantly improved roselle growth (plant height and number of branches/plant) as well as calyces fresh and dry weight as compared to control. This work was conducted in order to investigate on the effect of chemical and organic fertilizers on the growth and yield of Roselle.

Location and description of experimental layout
A field experiment was carried out during two consecutive summer seasons (2011 and 2012) in the Demonstration Farm of the Faculty of Agriculture, Omdurman Islamic University (Fitaihab), latitude 15⁰ 34 N, longitude 32⁰ 34 E and 393 m above sea level. The soil suffers from low depth and fertility with pH ranging between 7.0 -7. Two varieties of Roselle (Hibiscus sabdariffa L.) were used namely Bulk (as local variety, characterized by red stem and small seeds), which referred to as V1 and Omshiback (as certified variety, characterized by dark red stem and large seeds) referred as V2. The seeds of both varieties were obtained from Elobaied Research Station, Agriculture Research Station -Sudan (production of 2009/2010 season). The fertilizer treatments of the present study consisted of two chemical fertilizers (N and P) and two organic fertilizers (cow and chicken manure), in addition, to check treatments (F0). Nitrogen treatments were 40 kg N/fed (referred to as F1), 80 kg N/fed (referred to as F2), and a combination of 40 kg N/fed + 40 kg P 2 O 5 /fed (referred to as F3). Cow and chicken were firstly fermented in form of compost and then added as 3 tons/fed cow manure (referred to as F4) and 2 tons/fed chicken manure (referred to as F5). The process of formulation of both cow and chicken manure as compost was done according to Billington [17]. Sowing date was in the 3 rd week of July for both 2011 and 2012 seasons. The experiment was laid out in a split-plot design with four replications according to Gomez and Gomez [18]. The varieties were allotted in the main plots, whereas the fertilizers treatments were designated in the sub-plots.

Husbandry
Before sowing, the stable of the previous crops was removed from the experimental area. The land was then disc-plowed, leveled and then ridged at 70 cm spacing. The experimental unit was a plot of 12.5 m 2 (5 m × 2.5 m) in area and consist of 6 ridges, each 2.5 m in length. The crop was sown on 20 th July for the two seasons. Five seeds per hole were sown on the top of the ridge at 50 cm spacing between holes. Phosphorus, cow and chicken fertilizers were then applied on the bands of one side of the ridge at the depth of near 3 inches, while nitrogen fertilizer was broadcasted. The crop was immediately irrigated after sowing and then irrigated consequently every 7 days; accordingly, the crop received 14 irrigations during the season, which extended to about 4 months. Thinning to 2-3 plants/hole and re-sowing were carried out after the 3 rd irrigation for both seasons. Three manual weedings were done after the 3 rd , 5 th , and 7 th irrigation. No pesticides or fungicides were used in both seasons.

Growth and yield attributes
After the plant well established, five plants from the four central ridges in each plot (treatment) were randomly selected and tagged to study the following characters

Plant height (cm).
This parameter was measured for the five selected plants from the base immediately above the soil to the tip of the youngest leaf at 14 th week from sowing using tap meter and then plant height for each treatment was determined.

Numbers of nodes ∕ stem.
Nodes at the main stem from which leaves raised were counted at the 14 th week from sowing.

Number of leaves ∕plant.
This parameter determined every 15 days starting at 14 th week from the sowing up to maturity.

2.3.4.
Leaf area (cm 2 ). Randomly 5 leaves from 5 selected plants were taken fresh at 14 th week and then butchered using buncher, after that the disc and the rest leaves were air-dried and from their dry weight leaf area were calculated according to the formula: 2.3.5. Number of branches/plant. After 12 th weeks, all set-up branches in the five selected plants were account and then mean of number of branches/plant for each treatment was determined.

Plant dry weight (g).
From the two outer ridges of each plot, five plants were gently uprooted, air-dried and then frequently weighed using a me-teller sensitive balance. This measurement was taken 14 th week from sowing.

Dry calyx yield (kg∕ fed).
After 120 days from sowing, most fruits reached maturity in both seasons, when their capsules turned from green to yellowish color and started to crack at the tip. At this stage, fruits of plant in an area of 4.2 m 2 (6.0 m × 0.7 m ) in the 4 central ridges (1.5 m each) were picked from each plot. Then calyces were air dried and weighed to obtain calyces dry weight (kg∕ fed.) according to the equation:

Statistical analysis
Data were analyzed using Analysis of Variance (ANOVA) according to Gomez and Gomez [17]. Mean separation for the treatment means was done by using Duncan's Multiple Range Test (DMRT).

Plant height.
Table1shows that plant height in both seasons (2011 and 2012) was not significantly affected by Roselle varieties, although it was higher in V 1 (Bulk) than in V 2 (Omshiback) by about 20.6% for the 1 st season and 15.1% for the 2 nd season. Similarly, this parameter was also not significantly affected by application of different types of fertilizer, but table1 indicates that F 1 (40 kg N/fed.) in both seasons achieved in significantly higher mean of pant height (104.1 and 88.6 cm, respectively) than other fertilizer treatments.

Number of nodes/plant.
In both seasons, number of nodes/plants was slightly higher under V 1 (39.9 and 28.9, resp.) as compared to V 2 (34.2 and 27.7, respectively), but it was significantly different in the 1 st season. The slightly higher number of nodes for V1than V 2 resulted in plant height for this variety as shown previously. Application of chemical and organic fertilizers did not significantly affect number of nodes/plant of Roselle and F 1 treatment as shown in table1slightely increased this parameter than other treatments, but with no significant differences. Many studies indicate that the number of nodes is genetic control rather than environmental influences.

Number of leaves/plant
This parameter was statistically insignificant between varieties in both seasons, but it was significantly affected by fertilizer during the 1 st season (Table 1). During the 1 st season, F 1 reported a significantly higher mean of number of leaves/plant (169.7) in comparison of all other studied fertilizer treatments, except F 2 (140.3). This result may indicate the response of roselle plants to the low as well as high doses of N fertilizer in relation to the number of leaves/plant. This result was in line of Duke and Aychely [5], Van Damme and Viaene [3], Hago and Oman [13] and Abdelbagi [14].

Leaf area (cm 2 )
Table1 demonstrates that neither genotypes nor fertilizer application statistically affected leaf area of roselle and it was ranged between 10.5 cm 2 for V 1 during the 1 st season and 8.8 cm 2 for the same variety during the 2 nd season, and between 11.3 cm 2 for F3 during the 1 st season and 7.7 cm 2 for F 0 during the 2 nd season.

Number of branches/plant
Number of branches/plants did not significantly affect by genotype and fertilizers in both seasons as shown in Table 2. Although there were no significant differences between varieties for this character, but Table2 shows a slight increase in this character under V 1 as compared to V 2, particularly in the first season, when V 1 increased this parameter as compared to V 2 by about 18.0%. Similarly, F 1 in the 1 st season and F 0 in the 2 nd season obtained in significantly higher mean of this character as compared to the other treatments. The insignificant effect of application of fertilizer in this study towards plant height in both seasons and number of leaves in the 2 nd season may be behind the insignificant effect of these treatments on branches/plants.  Table 2 shows that plant dry weight of Roselle was not significantly affected by both genotypes and applied fertilizer in both seasons. It was observed that in both seasons, F 1 treatment reported in significantly higher mean of this parameter (40.1 and 35.5 g, respectively), which may be attributed to the better performance of this treatment regarding the vegetative growth as shown previously.

Dry calyx yield (kg∕ fed.)
Yield of dry calyx as shown in table 2 was not significantly affected by both genotype and application of chemical and organic fertilizers, but it was observed that it was insignificantly increased in V 1 than in V 2 by about 19.0% for the 1 st season and 21.4% for the 2 nd season, which may indicate better performance of this variety regarding growth and yield components. On the other hand, both F 1 in both seasons achieved insignificantly higher dry calyces yield as compared to the other fertilizer treatments. The slight increment in dry calyces yield under this treatment may be attributed to its effect on growth parameters as well as yield components. Similar results were also reported by Adamson et al. [6] and Rhoden and small [7], Krishnamurthy et al. [11], Gibson and Waring [19], Hago and Oman [13], Hago et al. [20] and Abdelbagi [14].

Conclusion and Recommendation
Based on the findings of the present study it could be concluded that although most studied growth and yield parameters were not significantly affected by chemical and organic fertilizers, but it was observed that slight insignificant increasing in these parameters under fertilizer treated plants, and hence it recommended that further studies related to types and levels of fertilizer should be carried out.