Tropical Soil Labile Fractions of Copper in the Experimental Plots ±Ten Years after Application of Copper-Containing-Waste

Copper is reported to be retained in soils for a quite long time particularly in soil treated with some amendments. This research was intended to evaluate the soil labile fractions of Cu ±10 years after application of Cu-containing industrial waste, lime, and cassava-leaf compost. Soil samples were taken from topsoils and subsoils of ±10 years old experimental plots set up in 1998 and factorially treated with a metal-spoon industrial waste at 0, 15, and 60 Mg ha-1, lime at 0 and 5 Mg ha-1, and cassava-leaf compost at 0 and 5 Mg ha-1. The measured Cu labile fractions were compared to those in soils sampled at ±1.5 years and ±3 years after treatments. The results showed that the soil Cu labile fractions in waste treated soils were higher than those in the control treatments eventhough their concentrations decreased with the years of sampling. Lime showed a decreasing effect on soil labile Cu fractions, but the effect decreased with the years of sampling. The effect of cassava-leaf compost application on soil Cu labile fraction was in general not evidenced ±10 years after treatment.

Effects of biochar on the fate of the heavy metals Cd, Cu, Pb and Zn in soil

An in vitro incubation study was conducted with soil having seven applications of different treatments of biomass and biochar including a control. The biochar and biomasses were applied at a rate of 5 t ha-1 and incubated at field moisture condition for 30, 60 and 90 days individually in different pots. 0.005M DTPA and 1M HCl extractable cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) contents were determined at 30, 60 and 90 days of incubation. The phytoavailable fraction of Cd, Cu, Pb and Zn as extracted with the 0.005M DTPA revealed that biochar did not retain any substantial amount of any of these metals. 1M HCl extracted higher amounts of heavy metals than 0.005M DTPA. Neither biochar nor its source biomass had any sorptive effect on the labile fraction of Pb and Cd present in soil. 1M HCl extracted not only a portion of these metals from the soils but also that present in the biochar and biomass. The general idea that biochars are able to complex metal ions on their surfaces and therefore, reduce bioavailability, however, was not reflected in the present study.Bangladesh J. Sci. Res. 28(1): 17-26, June-2015