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Khan N.,University of South Australia | Clark I.,University of South Australia | Bolan N.,University of Newcastle | Meier S.,University of the Frontier | And 6 more authors.
Journal of Soils and Sediments | Year: 2016

Purpose: The purpose was to develop a netbag technique suitable for burying biochar in a compost or composting medium, followed by its collection in a clean state (i.e., free of compost debris) without loss or damage, for physicochemical analyses. Collection in a clean state is required to ensure that the analytical data of various biochars are representative and comparable. Five criteria were identified to evaluate the suitability of netbag. Materials and methods: A small netbag (3.5 × 3.5 cm) was developed using nylon fabric (30-μm mesh) to contain ∼1 g of biochar. A production system was developed to make 15 netbags per batch. Unlike commonly used litterbags, polypropylene was used to seal netbags. Two experiments were conducted in which three biochars, made from macadamia nutshell, hardwood shaving, and chicken litter, were co-composted with chicken manure and sawdust and also incubated with a chicken litter-based commercial compost. Biochars were added at the rates of 5 or 10 % in the co-composting and 10 or 20 % in the incubation experiments. The biochar-containing netbags were buried in the co-composting and incubation mediums for 133 days. Various physicochemical analyses were conducted with netbag-biochars and their compost mediums. Results and discussion: The netbags collected after both experiments showed no visible sign of degradation. The weight of netbag-biochars from co-composting and incubation systems did not reduce significantly over the experimental period, thereby indicating no loss of biochar. No visible evidence of entry of solid particles from compost medium was found on the netbag-biochars. Pretests indicated that the netbag and biochars absorbed pore solution from the medium. Findings showed that elements translocated between the netbag-biochar and compost medium. A colony of coccus bacteria was found on the surface of composted chicken litter biochar, denoting probable entry of bacteria from compost medium. Unlike conventional litterbags, the netbags were suitable for burying and extracting biochar in compost/composting mediums due to smaller size, smaller mesh, and strong sealing with polypropylene. Conclusions: The netbags addressed all the five criteria. Therefore, it was concluded that, in the co-compost or incubated-compost medium, the biochar retained in the netbag and the biochar mixed with the medium were exposed to a similar bio-oxidative environment, and netbag-biochar represents the biochar in the medium. This means that these netbags can be used as a convenient means to examine the effects of the composting process or incubation in compost on biochar. © 2016 Springer-Verlag Berlin Heidelberg Source


Khan N.,University of South Australia | Seshadri B.,Cooperative Research Center for Contaminants Assessment and Remediation of the Environment | Seshadri B.,University of New South Wales | Bolan N.,Cooperative Research Center for Contaminants Assessment and Remediation of the Environment | And 17 more authors.
Advances in Agronomy | Year: 2016

Loading of nutrients and contaminants is increasing in wetlands due to anthropogenic activities. The scope of this paper is to (1) provide an overview of natural, cultivated, and constructed wetlands and hydrophytes, (2) characterize root iron plaque of hydrophytes, (3) show roles played by root iron plaque as a source and sink for nutrients and contaminants for hydrophytes, (4) present toxicity tolerance mechanisms employed by hydrophytes, and (5) offer implications of the findings about iron plaque, and (6) to suggest future research. Iron plaque deposits on hydrophyte root surfaces are a result of oxidation of ferrous iron in the oxic rhizosphere under waterlogged conditions in wetlands. The iron plaques mainly consists of amorphous and crystalline iron oxyhydroxides. They, therefore, can sequester nutrients and contaminants that can bind to iron oxides. Recently advanced spectroscopic techniques, such as synchrotron radiation techniques, have been used to identify and characterize iron plaque components. Sequestration and plant uptake of these materials mainly depend on the available nutrients and contaminants, oxygen diffusion capability of hydrophyte roots, and bio-physico-chemical properties of the rhizosphere. Root iron plaque plays a vital role in controlling the sequestration of excess loads of nutrients and contaminants in wetlands. © 2016. Source

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