Effects of Agro-Industrial Waste on the Phytoremediating Potential of sunflower in Hydrocarbon-Contaiminated Soil.
This study investigated the growth performance and yield of sunflower (Helianthus annuus L.) under different concentrations of petroleum hydrocarbon contaminated soils. This was with a view to assessing the phytoremediating potentials of the test crop when different agro-industrial wastes were applied as soil enhancers. The study was carried out at the screenhouse of the Faculty of Agriculture, Obafemi Awolowo University, Ile-Ife. Poultry droppings were collected from the University Teaching and Research Farm and composted. Sawdust was collected from sawmills along Road Seven, Ile-Ife and ashed. The composted poultry manure and the ashed sawdust were mixed at different ratios [0:100 (PW0SD100), 25:75 (PW25SD75), 50:50 (PW50SD50), 75:25 (PW75SD25), 100:0 (PW100SD0)] to act as enhancers. Bulk surface soil sample from an exhaustively cropped land was collected, air-dried and sieved through a 2 mm mesh. One hundred and thirty five pots with perforations at the bottom, each with five kilograms of the air-dried soil was contaminated to different levels (0, 1, and 2%) of crude oil from Nigerian National Petroleum Corporation, Eleme, Rivers State. The manures were applied at the rates (0, 4, 8 t ha-1) two weeks before planting of sunflower seeds and pots were watered to field moisture capacity with distilled water. Viable seeds of sunflower from Institute of Agricultural Research and Training, Ibadan were sown at four seeds per pot and the emerged seedlings were thinned to two stands per pot two weeks after sowing. The pots were maintained weed-free throughout the experimental period. Growth parameters (plant height, stem girth, number of leaves and leaf area) of sunflower were measured fortnightly. The root, shoot and grain yield of sunflower were harvested at full maturity and analysed for Pb, Cd and total petroleum hydrocarbon (TPH). Pre and post cropping analyses of soils were carried out to determine the nutrients, Pb, Cd and TPH using standard methods. Data obtained were subjected to ANOVA and descriptive statistics. Seedling emergence was recorded in all the pots and they all survived till the end of the growing period, except for 2% crude oil contaminated pots without 100% and 75% poultry wastes. Highest growth performance was recorded in pots with no contamination but with PW100SD0 (186 cm, 36, 3.8 cm, 141 cm2 and 23.0 g /pot) while the control pots had the least growth performance of 117 cm, 12, 2.0 cm, 19 cm2 and 16.8 g/pot) for the plant height, number of leaves, stem girth, leaf area and shoot yield respectively. The highest uptake values of Pb, Cd and THC in the shoot were: 0.99, 1.01 and 1.98 mg kg-1 while the roots: 1.78, 1.80 and 1.74 mg kg -1respectively at 2% contamination when 8 t ha-1 of PW100SD0 was applied. The uptake of Pb 0.43, Cd 0.48 and TPH 0.83 mg kg-1 was obtained in the grains at 2% contamination when 8 t ha-1 of PW100SD0 was applied. Addition of composted poultry manure and ashed sawdust increased the soil acidity by 18% and this enhanced the bioavailability of other soil properties. The study concluded that sunflower plant could be effectively used for the remediation of petroleum hydrocarbon-contaminated soils and poultry manure compost mixed with ashed sawdust enhanced the remediating ability.