Effect of Biochar Amendment on Heavy Metals Concentration in Dumpsite Soil and their Uptake by Amaranthus (Amaranthus cruentus)

A pot experiment was conducted in screen house of Faculty of Agriculture, Nasarawa State University Lafia, Nigeria during the dry season of 2014 to assess the presence of heavy metals and the effect of biochar on the concentration of these heavy metals in dumpsite soil and their uptake by Amaranthus (Amaranthus cruentus). Five kilogram of dumpsite soil was filled into 27 plastic buckets. The experimental design used was completely randomized design (CRD) and the treatments consisted of three levels of both sawdust and rice husk biochars: 0, 60, 120 g, factorially combined to form 9 treatments and laid out in the screen house. The result revealed that the dumpsite soil was contaminated with heavy metals and their concentration in ascending order in the soil is as follows: Pb< Cd< Ni < Zn< Mn. Only Cadmium (3.7 mgkg-1) was above FEPA allowable limit of 3 mgkg-1. There was a significant (p< 0.05) decreased in soil cadmium, nickel and manganese when both biochars were incorporated into the dumpsite soil. Application of 120 g of rice husk biochars reduced the concentration of cadmium (0.27 mgkg-1), nickel (0.53 mgkg-1) and manganese (0.66 mgkg-1); but increased the concentration of lead (1.79 mgkg-1) and zinc (6.82 mgkg-1) in the soil. Also, 120 g of saw dust biochar reduced the concentration of cadmium (0.27 mgkg-1), nickel (0.55 mgkg-1) and manganese (0.71 mgkg-1). Both rice husk and sawdust biochars rates applied in dumpsite soil significantly (p< 0.05) reduced the quantities of manganese uptake by amaranthus plant. However, the uptakes of cadmium, zinc, lead and nickel by amaranthus were not significantly (p< 0.05) affected by the application of different rates of both rice husk and sawdust biochars; but an increased in both biochars applied on dumpsite soil resulted to a gradual decrease in the entire heavy metals uptake by amaranthus plant. The combined effect of rice husk and sawdust biochar did not showed any significant effect on the concentration of heavy metals in dumpsite soil and subsequent uptake by Amaranthus.