Abstract
The objective of this work was to determine the contribution of dissolved organic carbon (DOC) from a biochar mineral complex (BMC), so as to better understand the interactions between DOC, biochar, clay, and minerals during thermal treatment, and the effects of BMC on amended soils. The BMC was prepared by heating a mixture of a H3PO4-treated saligna biochar from Acacia saligna, clays, other minerals, and chicken manure. The BMC was applied to a sandy loam soil in Western Australia, where wheat was grown. Liquid chromatography-organic carbon detection (LC-OCD) tests were carried out on water extracts from the untreated biochar, the BMC, the BMC-amended soil, and on a control soil to measure the DOC concentration. LC-OCD tests provide a fingerprint of the DOC, which allows the fractions of DOC to be determined. Thermal processing enhanced the reaction of the A. saligna biochar with manure, clays and minerals, and affected the distribution of the DOC fractions. Notably, the process leads to immobilization of hydrophobic DOC and to an increase in the concentration of low-molecular-weight neutrals in the BMC. The application of the BMC to soil increases the DOC in the amended soil, especially the biopolymer fraction.
Highlights
Dissolved organic carbon (DOC) or water-extractable organic carbon (Weoc) represents a small proportion of soil organic matter, but plays many roles in the soil ecosystem, largely due to its mobility and reactivity, affecting soil biological activity, transporting metal contaminants and mineral weathering (Chantigny, 2003).The amount of dissolved organic carbon (DOC) has been correlated with the soil microbial production of CO2 and dehydrogenase activity (Rees & Parker, 2005)
The X-ray photoelectron spectrometry (XPS) analysis showed that carboxylic carbon was not detectable on the surfaces of the untreated and H3PO4-treated saligna biochar, and the carbon was mainly (88–89%) in a C–C/C–H bonding state (Table 1)
The H3PO4-treated biochar showed a slight increase in the concentration of C–O bonds
Summary
Dissolved organic carbon (DOC) or water-extractable organic carbon (Weoc) represents a small proportion of soil organic matter, but plays many roles in the soil ecosystem, largely due to its mobility and reactivity, affecting soil biological activity, transporting metal contaminants and mineral weathering (Chantigny, 2003).The amount of DOC has been correlated with the soil microbial production of CO2 and dehydrogenase activity (Rees & Parker, 2005). Based on studies of environmental controls on dissolved organic matter concentrations and fluxes in soils, Kalbitz et al (2000) indicated that litter and humus are the most important DOC sources in soils. DOC can be trapped within mineral soils by adsorption, which can result in its immobilization and stabilization (Schneider et al, 2010). This may be strongly associated with Fe and Al oxides and oxyhydroxides (Kothawala et al, 2009). The adsorption-desorption equilibrium between the dissolved phase and the solid phase of soil organic matter depends on the colloidal properties of soils, such as their ionic strength, valence of the involved cation, and pH value (Münch et al, 2002)
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