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Study on the effect of biochar addition to soil artificially contaminated with zinc

Koutsoubi Maria-Eleni

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Summary

The purpose of the present study was to evaluate the influence of biochar in soil properties and zinc availability. Biochar was prepared through pyrolysis of olive pomace in a muffle furnace at 700 °C. Three different biochar amendment rates were tested (0, 5 and 10%), as well as two different zinc concentrations (1,000 και 2,000 mg/(kg of soil)). Moreover, blank assays were conducted, in which soil was mixed with biochar at the same amendment rates and where instead of a metal solution deionized water was used. During the experiment that lasted for a period of 30 days, all mixtures were sampled on the 1st, 10th, 20th and 30th day in order to determine soil pH, Electrical conductivity and Redox potential, while samples taken on the 30th day were subjected to phytotoxicity assays using three different seeds’ species. All contaminated soil samples were also analyzed regarding zinc mobility and availability through single extraction procedures, while a sequential extraction procedure was carried out only for the samples taken on the 30th day.According to the results, biochar addition to soil, generally led to increased pH, Cation Exchange Capacity and Electrical conductivity values, as well as to reduced Redox potential values. The concentrations for EDTA-extractable zinc reached much higher levels than those of CaCl2- and DW-extractable zinc. Τhe addition of biochar to soil reduces the mobility and availability of zinc, which can be attributed mainly to the observed rise in pH and cation exchange capacity. Through the sequential extraction procedure that was followed it was made clear that the presence of biochar causes changes in zinc distribution among soil fractions. More specifically, results showed that biochar addition to soil increased the portion of the metal bound to the Residual fraction while the one bound to the Exchangeable fraction was decreased. Thus, amending soil with biochar contributes to reduction of zinc extractability. Regarding the results of phytotoxicity assays, the presence of zinc in soil samples had a negative influence on seed germination and growth of the roots of the three plant species. On the contrary, biochar amendments led to an increased number of germinated seeds, as well as to elongation of the roots. Generally, higher biochar amendment rate was associated with better results, with the exception of phytotoxicity tests where results were opposite.

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