Abstract
Present work aimed at evaluating the leaching potential of grape husks biochar, municipal solid wastes compost and their combined application as amendments of sandy Mediterranean soil, in order to assess their capability of releasing/retaining nutrients or heavy metals and therefore their suitability for agricultural applications. Grape husks biochar was produced by pyrolysis at 500 °C in a fixed bed unit. Column leaching experiments, simulating Mediterranean rainfall conditions, were conducted. For all compost/biochar/soil combinations, alkali and alkaline earth metals showed greater solubility, increasing the pH of the extracts and thus decreasing the leachability of heavy metals Cr, Cu, Zr and Sr. Biochar co-application with compost did not prevent the leaching of nitrates, phosphates or trace elements; however, it did lower the chemical oxygen demand and allowed the slower release of sodium, calcium and magnesium from soil. As compared to compost, addition of biochar to soil increased the concentration of potassium by 76%, whereas it decreased that of heavy metals in the leachates by 40%–95%. Grape husks biochar could serve as a better soil amendment than municipal solid wastes compost and if carefully managed could be used as liming agent or fertilizer on acidic soils.
Highlights
The intensification of agricultural production to satisfy global needs has a negative impact on soil fertility, especially in regions with higher temperatures, such as Mediterranean
The upper soil horizon sampling is a common practice in agronomical applications, when the effect of amendments or pollutants on crops is studied, or when soils/wastes are amended with additives prior to cultivation
The present findings suggest that grape husks sorption, electrostatic attraction and competition between
Summary
The intensification of agricultural production to satisfy global needs has a negative impact on soil fertility, especially in regions with higher temperatures, such as Mediterranean. Large quantities of residues are generated, the management and disposal of which may create environmental problems. Compost produced from organic waste under aerobic conditions through mineralization and humification is commonly used to ameliorate the physical, physicochemical and biological properties of soils by increasing their organic carbon, replenishing various nutrients for plant growth, and saving fertilizers [2,3]. The degradation of organic compounds during composting can change the properties of waste biomass and increase the content of mobile forms of heavy metals, causing soil contamination [3,4]. This problem applies to composts originating from municipal solid wastes (MSW). Nutrient fluxes to the plants, especially nitrogen and phosphorous, should be carefully managed to avoid eutrophication or pollution of water sources [3]
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