Summary
This study was conducted at laboratories of College of Science, University of Salahaddin – Erbil for Assessment the effect of oil refinery residues on enzymatic activity, respiration rate, nitrification and denitrification in two textured soils.
A factorial completely randomized experimental design was implemented including two factors with three replications, the first factors involved two soil texture (sandy loam and clayey); while the second factor involved seven refinery oil residues levels (0, 5, 10, 15, 20, 25, 30 ml) with their combinations effect on enzymatic activity, respiration rate, nitrification, denitrification, pH, electrical conductivity and total number of bacteria and fungi. Hence 14 experimental treatments were tested with replicates making the total of 42 experimental units.
The summary of the main results was as follow:-
- The results of the present study show that soil characteristics are playing an important role in controlling the effect of crude oil residues on the activities of soil enzyme.
- The highest values µg N.g-1 soil, µg H2O2 .g-1 soil and 70.825 µgTPF.g-1 soil for urease, catalase and dehydrogenase were recorded in 15ml of oil residues and control treatments respectively.
- The activity of urease and catalase were increased by 26.729 and 36.946 % respectivelywhile dehydrogenase activity in soil treated by oil residues was decreased by 61.570 % control
- Oil residue levels were significantly (p≤0.05) affected on soil respiration rate at 3 and 4 days of incubation except 2days of incubation show non-significant differences. The highest value 4.893 gC-CO2.m-3.day-1 was recorded in 20ml of oil residue for 3days incubation, while the lowest value 1.228gC-CO2.m-3.day-1 was recorded in the control after 4days incubation.
- A significant positive correlation between the levels of oil residues and soil respiration rate were recorded with correlation coefficients r=0.991** and r=0.986** for 3 and 4days
- The combination between soil texture and different levels of oil residue were significantly (p≤0.05) affected on soil nitrification rate. The highest value 96.179mg.kg-1 was recorded by combination treatment control of sandy loam soil. While the lowest value 76.915mg.kg-1 was recorded in the combination treatment 20ml of oil residues and clayey soil.
- The highest value 90.602mg.kg–1 1
- The oil residue levels were significantly (p≤0.05) affected on denitrification in studied soils. The highest value was
- The significant negative correlation (r = −0.877**, P ≤ 0.05) observed between the levels of oil residues and denitrification.
- The pH of soils treated with oil residues decreased with the increased amounts of the oil level except 30ml oil residue the pH increased over control.
- Oil residue levels were significantly (p≤0.05) affected negatively on EC of soils under the study. The highest values was 271.083 μS.cm-1 recorded in control. While, the lowest value 151.167μS.cm-1 was recorded in the 30ml of oil residues treatment. The EC of soil treated with oil residues decreased by 44.236 % over control.
- Soil texture was significantly (p≤0.05) affected total number of bacteria and fungi. The highest value for total number of bacteria 28.171× 105 CFU g-1soil was recorded from sandy loam soil (S1). In contrast the highest value of total number of fungi 56.342× 10³ CFU g-1soil recorded from clayey soil.
- The total number of bacteria and fungi in soils positively correlated with increasing oil residue levels with correlation coefficients (r=0.672 and r=0.937**) respectively. The highest values were 25.883× 105 CFU g-1soil and 78.767×10³ CFU g-1soil recorded in 10ml and 30ml of oil residue treatments.
- Combination of soil texture and levels oil residue were affected (p≤0.05) the total number of bacteria and fungi. The highest values 44.800×105 CFU g-1soil and 126.333×10³ CFU g-1soil recorded by combination treatment 10ml of oil residue in sandy loam soil and 30ml of oil residue in clayey soil for total bacteria and fungi respectively.
13-12-2016