Effcacy of fresh and air-dried biosolids as amendments for remediation of acidic and metal-polluted soils: A short-term laboratory assay

Biosolids have been used as amendments on mine degraded soils for in situ immobilization of metals, neutralization, and improvement of nutritional, microbiological, and physical characteristics to reestablish a self-sustaining plant community. Fresh and air-dried biosolids have been used but dried ones are preferred as they are cheaper to transport, contain less pathogens and are much easier to handle. The same effcacy has been assumed for both biosolids. The study evaluated the effects of fresh and air-dried biosolids on physical, chemical and microbiological characteristics of an acidic and metal/As-rich soil of the Puchuncaví valley, central Chile, and on plant yield under laboratory conditions. Two doses of each biosolids were used (50 and 100 ton ha^-1, dry weight). Fresh and air-dried biosolids similarly increased organic matter, total nitrogen (N) and available N and phosphorous contents of study soil. However, air-dried biosolids exhibited lower feld capacity and higher wilting point, salinity, higher levels of dissolved organic carbon, concentrations of total dissolved copper and zinc, and lower activity of free Cu²⁺ ions in pore water. Basal respiration was signifcantly increased by incorporation of biosolids into soils, irrespective of being fresh or air-dried ones. In terms of aerial plant productivity, fresh biosolids and low doses of air-dried biosolids signifcantly increased this characteristic. However, high doses of air-dried biosolids limited aerial biomass and root cover, probably due to soil salinity and water stress. Therefore, fresh biosolids are suggested for remediation of this mine degraded soils.