PHYSICAL PROPERTIES AND MAIZE PRODUCTION IN A SPENT OIL-CONTAMINATED SOIL BIOREMEDIATED WITH LEGUMES AND ORGANIC NUTRIENTS

Information on the use of plant species and organic nutrients to improve the physical properties of oil-contaminated soil, with a view to making it conducive for crop production, is very important. Three legumes (Gliricidia sepium, Leucenae leucocephala and Calapogonium caeruleam) combined or not with poultry manure were tested for their ability to improve the physical properties of a sandy soil, contaminated with 5% (w/w) spent lubricating oil, each for two years, and its effects on the growth and yield of maize in south eastern Nigeria. Aggregate stability (MWD), saturated hydraulic conductivity, and macro-to micro-porosity ratio improved with time in all the treatments over the 5% oil contamination (A5) and control. At 12 and 18 months, the use of Gliricidia sepium with 0.5% (w/w) poultry manure (A5+Gl+PM) gave the highest improvement of 58% and 94% in MWD, corresponding to 136% and 187% improvement in saturated hydraulic conductivity, respectively over the A5. The A5+Gl+PM also enhanced soil aggregate sizes > 0.25 mm by 63.6% and showed a 3-fold positive modification in soil macro-porosity. Positive relationships, significant at 0.01 level of probability, were observed between crusting hazard (R) and soil organic matter (r = 0.814), microporosity (r = 0.686) and saturated hydraulic conductivity (r = 0.787). The A5+Le+PM also increased maize growth and grain yield. Gliricidia sepium and Leucenae leucocephala combined with.0.5% (w/w) poultry manure is recommended for follow-up investigation, as it may offer a viable choice for remediation of oil-contaminated soil.


INTRODUCTION
The global emphasis on soil health and sustainable food security is persuading soil scientists to consider rehabilitation of degraded lands, especially where oil-contamination limits the use of such soils.The indiscriminate discharge of petrol oils and grease into farmlands, open vacant plots and water drains is becoming an acute environmental problem in Nigeria, particularly when large areas of agricultural land are contaminated (Atuanya, 1987).Government efforts to monitor, control and/or regulate these activities have proven to be very difficult because of paucity of information on the incidence of these activities Thus, contamination of agricultural ecosystems arising from discharge of petrol oils and grease with significant levels of hydrocarbons and other properties present in all petroleum products is more widespread than crude oil pollution (Atuanya, 1987).
Depletion in the nutrient status (nitrogen and phosphorus), inhibition of microbial activities and degradation of soil physical properties have been reported in spent oil impacted soils (Atlas and Bartha, 1993;Kirk et al., 2005).Formation of waxy texture in soils contaminated with spent lubricating oil has been (Anoliefo and Vwioko, 1995).The formation of oily scum which impedes oxygen and availability of water to biota as well as the formation of hydrophobic micro-aggregates with clay surfaces (Amadi et al., 1993;Rasiah et al., 1990), are associated with oil-contaminated soils.Decrease in soil water retention capacity at high potential  as a result of oil succeeding water in the competition for pore spaces and reduction in water film thickness around macro-aggregates, are a few other effects of oil in soil (Rasiah et al., 1990).
The use of green plants and organic nutrients to reclaim soils contaminated with petroleum products has recently become a subject of intense scientific interest in bioremediation technologies.However, the major focus has been on heavy metal attenuation and other chemical properties (Merkl et al., 2005;Harayama et al., 2004;Gallizia et al., 2003).Information regarding the use of some legumes and organic nutrient to improve the physical properties of oil-contaminated soil, with a view to making it available for crop production, is limited.
To evaluate the impact of bioremediation techniques on oil-contaminated soils, it is necessary to quantify the modifications in the soil physical properties, since they are the most important properties affecting crop production.Hence, the objective of this study was to evaluate the impact of three legume plants combined or not with poultry manure on the physical properties of spent lubricating oil-contaminated soil and relate such changes to maize performance.Furthermore, since the selected legume plants comprise widespread cultivated species, results have worldwide importance in countries beyond Nigeria.

MATERIALS AND METHODS
This study was carried out on 45 plots (each measuring 2.5 x 1.5 m) at the University of Nigeria, Nsukka, Research Farm (Lat.06 0 52'N, and Long.07 0 24'E).The soil is sandy loam (Typic Kandiustult) (Nwadialo, 1989) with low organic matter (Table 1).The plots were impacted with equivalent of 50,000 mg kg-, 1 (5% w/w) mono-and multi-grade crankcase oils from petrol and diesel engines, together with gear oils and transmission fluids and applied in a single dose each for two years.By the second year, oil contaminated plots had spent oil application of 100,000 mg kg-1 representing a total oil load of 10% (w/w).Three (3) legumes: Calapogonium caerulean, Gliricidia sepium, and Leucaena leucocephala combined or not with equivalent of 500 mg kg -1 (0.5% w/w) of poultry manure were used to enhance biodegradation.The experiment was arranged as a Randomized Complete Block Design (RCBD), with nine (9) treatments, viz: uncontaminated (control) soil (C), 5% spent oil (A 5 ), 5% spent oil + Calapogonium spp.(A 5 +Ca), 5% spent oil + Gliricidia spp (A 5 +Gl), 5% spent oil + Leucenae spp (A 5 +Le), 5% spent oil + Calapogonium spp.+ 0.5% poultry manure (A 5 +Ca+PM), 5% spent oil + Gliricidia + 0.5% poultry manure (A 5 +Gl+PM), 5% spent oil + Leucaena spp.+ 0.5% poultry manure (A5+Le+PM) with five replications.The legume seeds and poultry manure were introduced during early rains to the plots, seven (7) days after the oil contamination and allowed to incubate for fourteen (14) days before planting the maize crop.The second application of 5% spent oil was done 360 days after the first application.

Laboratory Studies Water-Stable Aggregates and Aggregate Stability
Water-stable aggregate was measured by the Kemper and Rosenau (1986) wet-sieving method.In this procedure, 40 g soil samples of < 4.75 mm aggregates were placed on the top of a nest of sieves of diameters 2, 1, 0.5 and 0.25 mm, and presoaked in distilled water for 30 min before oscillating vertically once per second in water for 20 times, using a 4 cm amplitude.The percentage ratio of the resistant aggregates on each sieve, representing the water-stable aggregates (WSA), was calculated as: where, MR is the mass of resistant aggregate (g), and MT, the total mass of wet-sieved soil (g).Aggregate stability was measured by the mean-weight diameter (MWD) of water-stable aggregates (Kemper and Rosenau, 1986), calculated as: where, X i is the mean diameter of each size fraction (mm), and W i is the proportion of the total aggregate in each size fraction and n is the number of sieves used.The State of Aggregation (SOA) was calculated using the Yoder (1936) method as: SOA =A/Y … (3) where, A is the aggregated particles with diameter > 0.25 mm and Y the original weight of oven-dried soil.

Pore-Size
Distribution, Saturated Hydraulic Conductivity and Crusting Hazard.
Pore-size distribution was calculated using the Flint and Flint (2002) water retention data.Saturated hydraulic conductivity (K sat ) was determined by the constant head permeameter technique (Klute and Dirksen, 1986) as: QL AT.H where, Q is volume of water (cm 3 ) that passed through a cross sectional area, A (cm 2 ), T is time elapsed (sec.),L is length of core (m), A is the cross sectional area of the core (cm 2 ) and ∆H is hydraulic head difference (cm).Crusting hazard (risk of sealing) "R" was calculated and classified using the Van der Watt and Claassen's (1990)

RESULTS AND DISCUSSION Aggregate Stability and Hydraulic
Conductivity.
The mean weight diameter (MWD) of water stable agregates improved with time in all the treatments except in A 5 (soil contaminated with 5% spent oil without legumes and poultry manure) and in C (control soil) (Table 2).The MWD decreased from 1.718 mm at 3 months to 0.850 mm at the 24 months in the A 5, with marginal decreases from 1.361 to 1.242 mm in the control during the same period.At 12 and 18 months, the A 5 +Gl+PM gave the highest improvement of 58% and 94%, in MWD, respectively, and corresponding increases of 136% and 187% in saturated hydraulic conductivity over the A 5 (Table 3).This improvement shows that the use of Gliricidia sepium with 0.5% poultry manure is very effective in bioremediation of aggregate stability and saturated hydraulic conductivity of spentoil-contaminated soil.Saturated hydraulic conductivity, as low as 8.64 cm hr -1 , obtained for A 5 at 18 months (Table 3) indicates that the oil succeeded water in the competition for pore spaces, leading to reduction in water film thickness around macro-aggregates (Rasiah et al., 1990).Also, the relatively high value of 1.718 mm in MWD (Table 2), without corresponding increase in saturated hydraulic conductivity (10.15 cm hr-1 ) at 3 months (Table 3), was not surprising, as this may have been due to the formation of hydrophobic macroaggregates reported for similar soils by Amadi et al;(1993) and Kirk et al.,. (2005).After 24 months, the average improvement in aggregate stability was in the order of A 5 +Gl+PM > A 5 +Le+PM > A 5 +Gl > A 5 +Gl > A 5 +PM > A 5 +Ca+PM > A 5 +Le > A 5 +Ca > C > A 5 (Table 2), whereas saturated hydraulic conductivity was increased in the order of A 5 +Gl+PM > A 5 + Le+PM > A 5 +PM > A 5 +Ca+PM > A 5 (Table 3).Therefore, a combination of 0.5% poultry manure with Gliricidia sepium and Leucaena leucocephala positively improved both aggregate stability and saturated hydraulic conductivity of the spent oilcontaminated soil.Poultry manure with Gliricidia (A 5 +Gl+PM) enhanced soil aggregate sizes > 0.25 mm by 63.6% (Table 4).The use of poultry manure alone (A 5 +PM) led to improvement of 60.7% of aggregate sizes > 0.25 mm, indicating the effectiveness of poultry manure and Gliricidia sepium in improving aggregate sizes of these degraded soils.

Pore Size Distribution, Organic Matter and Crusting Hazard
Macro-porosity for A 5 soil was low, ranging from 7-9% (Table 5).The low macro-to microporosity in the A 5 soil was probably due to the formation of waxy texture by the oil (Anoliefo and Vwioko, 1995), which may impede oxygen and available water content of the soil.The Gliricidia sepium, in combination with 0.5% poultry manure (A 5 +Gl+PM), showed a 3-fold positive modification in soil macro-porosity over the A 5 at 18 and 24 weeks (Table 5).The positive role of Gliricidia and Leucaena spp. in enhancing the macro-porosity could be attributable to their ability to improve the soil organic matter (SOM) content (Table 6) and the influence of their root exudates on the rhizosphere soil (Merkl et al., 2005, Molina-Barahona et al., 2004).A combination of poultry manure with Gliricidia spp, Calapogonuim spp.and Leucaena spp improved the average soil organic matter by 23.2, 22.6 and 21.8 g Kg-1 , respectively after 24 months (Table 6), with concomitant reductions in crusting hazard of 11,11 and 10%, respectively compared with A 5 and the control (Table 7).The low average macro-porosity (8%) recorded for A 5 (Table 5) may result in the formation of structural crusts which according to West et al. (1992), is considered the best indicator of soil structure conditions as well as a realistic basis for understanding water movement in the soil, to assess the suitability of such soil for root growth and the activities and movement of soil organisms.The correlation analysis (Table 8) showed a significant (P < 0.01) positive relationship (r = 0.814) between crusting hazard (R) and soil organic matter (SOM) content, confirming the positive role of SOM in reducing soil crusting.The significant (P < 0.05) positive correlation between R and macro-porosity (r = 0.686) and saturated hydraulic conductivity (r = 0.787) was not surprising.The explanations are that increases in R (low crusting hazard) lead to increases in saturated hydraulic conductivity and macro-porosity, indicating that soil organic matter, saturated hydraulic conductivity and macro-porosity were modified by the treatments, thus reducing crusting in plots treated with organic nutrient and legume plants.Pagliai (1987)    The maize plant was adversely inhibited during the establishment and vegetative growth stages.When the oil load was increased to 10% (w/w) in the second planting year, the plants died before 72 DAP (Table 9).Several factors may have contributed to the death of the plants, among which may include: lack of adequate oxygen, decrease in soil water retention capacity, surface crusting, and other undesirable soil physical conditions.Similar observations have been made by Anoliefo and Vwioko (1995) in pepper (Capsicum annum L.) and tomato (Lycopersicon esculentum Miller) and for maize and sugar cane (Molina-Barahona, 2004) growth was higher (115.6 and 107.6 cm) for A 5 +Gl+PM during the first and second plantings, respectively (Table 9).Grain yield of 4.91 t ha, -1 obtained during the first planting and 8.25 t ha -1 during the second planting for A 5 +Gl+PM gave significantly (p < 0.05) higher yield than using the legume plants alone (A 5 +Gl , A 5 +Le, or A 5 +Ca).(Table 10).

CONCLUSION
Based on these results, spent lubricating oil inhibited the growth of maize, during the establishment and vegetative growth stages, leading to the death of the plants.However, Gliricidia sepium and Leucaena leucocephala, if combined with 0.5% poultry manure, are promising alternatives for bioremediation of the physical properties of spent oil-contaminated soils.It is inexpensive, efficient and environmentally compatible, and may offer a viable choice for oil-contaminated soil remediation for maize production.
Additionally, they are well-known and easy-to-manage cultivated species, of which if accumulation of toxic oil compounds in the leaves can be excluded, Gliricidia sepium and Leucaena leucocephala with 0.5% poultry manure, could be used for the remediation of oilcontaminated soils.

Table 1 : Some physical properties of the top (0.30cm) soil of the experimental sit- poultry manure and spent lubricating oil.
procedure as:

Table 4 : The state of aggregation (%) of the top 0-30 cm of the oil-contaminated soil as influenced by the treatments after 24 months.
LSD (0.05) Treatment = 4.252, Months = NS, T x M = NS .

Table 6 : Organic matter (g Kg -1 ) of the top 0-30cm of the oil contaminated soil as influenced by treatments after 24 months Table 7: Crusting hazard (%) of the top 0- 30 cm of the oil-contaminated soil as influence by treatments after 24 months.
LSD (0.05) Treatment = 1.440,Month = NS,T x M = NS has reported positive relationships amongst soil organic matter, aggregate stability and surface crusting.

Table 9 : Mean plant height (cm) of maize plant in oil -contaminated soil under different treatments at different growth stages.
. Plant Physical Properties and Maize Production in a Spent Oil-Contaminated Soil Bioremediated with Legumes

Table 10 : Effects of treatments on grain yield of maize Maize grain yield (t ha -1 )
Yields followed by different letters within the years are significantly different at p<0.05 NY = No Yield.