European Journal of Scientific Research - EuroJournals

Seedling Growth of Gmelina Arborea (Roxb) as Influenced by Crude Oil in Soil 402
for quick vegetal cover of erosion sites. The tree is also readily used in taungya or agrisilviculture
systems. G. arborea is popularly used in addition to the non – nitrogenous indigenous species like
Anthornatha macrophylla and Dialium guineensis in alley cropping. It is also locally used to demarcate
boundaries. As a result of it’s use as a timber tree, pulpwood, matchstick, ornamental, fodder,
fuelwood, bee forage and a shade plant, G. arbores is known to display multipurpose uses (Etukudo,
2000).
Severe ecological damage has occurred in the Niger Delta area where most of the oil industrial
activities are predominant (Agbogidi and Edema, 2003). Oil exploration and exploitation activities
though, with tremendous economic benefits, have been reported to have serious adverse effects on
plants and the environment (Agbogidi et al., 2005a; Ekpo and Nwankpa, 2005; Agbogidi and Ejemete,
2005; Agbogidi and Eshegbeyi, 2006). With the teaming population of Nigeria and high demand for
forest species in many endeavours including fuel wood, timber needs and as fodder, it has become
important to study the effects of crude oil contaminated soil on the seedling growth of Gmelina, which,
though an exotic species, has displayed multipurpose uses over the years. The objective of this study
was to investigate the seedling growth of Gmelina arborea as influenced by crude oil in soil.
Materials and Methods
The experiment was conducted in Delta State University, Asaba Campus with garden soil mixed with
various crude oil concentrations (0%, 4%, 8% and 12%) constituting the treatments. The crude oil used
was sourced from the Nigerian National Petroleum Corporation (NNPC), Warri, Nigeria. The oil had a
specific gravity of 0.864 gm -3 and API gravity of 38.9. The oil treated and the uncontaminated soils
were kept in 10 cm / 20 cm bottom – perforated poly pots. The 8 weeks old Gmelina seedlings already
sown in the departmental nursing were transplanted to the crude oil treated soils and the control soils; a
seedling per poly pot. The experiment was laid out in a randomized complete block design (RCBD).
There were therefore four treatments replicated four times. Each treatment comprised 8 poly pots. The
poly pots were watered to field capacity using watering can immediately after transplanting and
thereafter, every other day till the end of the trial following the method of Agbogidi and Ejemete
(2005) and Agbogidi et al. (2006a) and Agbogidi et al.(2006b). The seedlings were allowed to
establish in the departmental nursery beds. Growth variables were measured for three months starting
from one month after transplanting (MAT). Parameters assessed were plant height, number of leaves,
leaf area, collar growth and dry weight biomass. Plant height was determined with a meter rule at the
distance from soil level to the top of the terminal bud, the number of leaves was determined by visual
counting of the leaves, leaf area was determined by multiplying the length and breath measurements of
a leaf multiplied by the number of leaves in the plant and finally by a correction factor of 0.75
following the procedure of Agbogidi and Ofuoku (2005). Girth growth at 3 cm above soil level was
determined using veneer calipers. The dry weight biomass was determined after the seedlings were
harvested at 3 MAT, sorted out into roots, stems and leaves and oven dried at 85ºC for 22 hours
following the methods of Anon (1966) and Agbogidi et al. (2005b).
Data collected were subjected to analysis of variance while the significant means were
separated with the Duncan’s multiple range tests using SAS (1996).
Results and Discussion
Significant reductions (P = 0.05) in the Gmelina seedlings were observed in all the parameters assessed
on monthly intervals with increasing oil level throughout the experimental period when compared with
seedlings grown in the uncontaminated soils (Tables 1, 2, 3, 4 and 5). The performance of the seedlings
in terms of height, number of leaves, leaf area, girth growth and dry biomass was poorer as the level of
oil contamination in soil increased. For example, growth stagnation and stunting were observed for
seedlings subjected to soils that received 12% oil treatments while the seedlings in the control soil
grew normally.