The effects of biochar on trace element and nutrient solubility in the presence of low-molecular-weight organic acids

Heaney, N

Abstract

Low-molecular-weight organic acids (LMWOAs) secreted by plant roots play an essential role in regulating the phytoavailability of soil-borne trace elements and nutrients. Biochar is widely considered as a suitable soil remediation option, having shown an efficacy to retain both anions and cations. This study aims to unravel the roles of LMWOAs in affecting the functioning of biochar in aqueous and soil systems. Twelve biochar were characterised and rice husk biochar was selected for use. Firstly, aqueous batch experiments examined the biochar-driven immobilisation of trace elements and nutrients with and without LMWOAs. Then, batch studies tested if biochar would reduce the LMWOA-driven solubilisation of trace elements and nutrients in soil. Later, rice husk biochar and LMWOA-activated rice husk biochar were incorporated in greenhouse investigations to study the growth parameters of edible plant species and trace element uptake by pea (Pisum sativum). Solution sorption studies found that LMWOAs impeded the biochar-driven removal of cadmium and lead but enhanced nitrate removal. Biochar did not affect phosphate removal. Biochar inhibited the LMWOA-driven solubilisation of soil-borne cadmium and zinc. Nitrate immobilisation was not enhanced but biochar reduced the immobilisation of the added nitrate overall. Phosphate immobilisation was observed but was caused by the precipitation of practically insoluble phosphate minerals using biochar as a source of soluble calcium. Seven out of eleven trace elements accumulated in pea roots were reduced either by biochar and LMWOA-activated biochar but the uptake was variable with biochar type. The data obtained indicate LMWOAs complicate biochar functioning in solution and soil under the studied conditions. Based on the results, protonation of the biochar materials in acidic conditions impeded cation immobilisation whilst enhancing nitrate immobilisation. Acid neutralisation by the biochar materials likely reduced the LMWOA-solubilisation of trace elements which would affect trace element uptake by plants such as pea, within biochar-amended soils.

Citation

Heaney, N. The effects of biochar on trace element and nutrient solubility in the presence of low-molecular-weight organic acids. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Feb 12, 2020
• Publicly Available Date: Feb 12, 2020
• Award Date: Jan 1, 2020