An incubation experiment was conducted to investigate themicrobial biomass associated Cu in four contrasting soils to which analkaline stabilised sewage sludge cake was applied. The organisms ofsludge- amended and control soils were killed using γ-irradiationtechnique, and the aqueous and acid-extractable Cu concentrationswere determined. Addition of the sludge product increasedsignificantly the concentration of both the aqueous and diluteHOAc-extractable Cu in all the irradiated soils compared to thenon-sterilised sludge/soil mixtures, but the increase was morepronounced in the dilute acid-extractable Cu, indicating that the Curendered extractable in water and dilute acetic acid by γ-irradiation existed in the both soil liquid and solid phases. Theadditional increase in extractable Cu following the biocidaltreatment is likely to be due to release of Cu from the same fractionof soil microbial biomass.
Fractionation of metals in acid sandy loam soil amended withalkaline-stabilised sewage sludge biosolids was conducted in order toassess metal bioavailability and environmental mobility. Soilsolution was extracted by a centrifugation and filtration technique.Meal speciation in the soil solution was determined by a cationexchange resin method. Acetic acid and EDTA extracting solutions wereused for extraction of metals in soil solid surfaces. Metaldistribution in different fractions of soil solid phase wasdetermined using a three-step sequential extraction scheme.
LUO YONGMINGInstitute of Soil Science, the Chinese Academy of Sciences, Nanjing 210008 (China)
Copper (Cu) mine tailings, because of their high content of heavy metals, are usually hostile to plant colonization. A pot experiment was conducted to determine the tolerance of four forage grasses to heavy metals in Cu mine tailings and to examine the variation in the microbial functional diversity of soils from the tailing sites in southern China. All the four grass species survived on Cu mine tailings and Cu mine tailing-soil mixture. However, on pure mine tailings, the growth was minimal, whereas the growth was maximum for the control without mine tailings. The tolerance of grasses to heavy metals followed the sequence: Paspalum notatum 〉 Festuea arundinaeea 〉 Lolium perenne 〉 Cynodon daetylon. The planting of forage grasses enhanced the soil microbial biomass. The Biolog data indicated that the soil microbial metabolic profile values (average well color development, community richness, and Shannon index) of the four forage grasses also followed the sequence: P. notatum 〉 F. arundinaeea 〉 L. perenne 〉 C. daetylon. Thus, P. notatum, under the experimental conditions of this study, may be considered as the preferred plant species for revegetation of Cu mine tailing areas.
TENG YingLUO Yong-MingHUANG Chang-YongLONG JianLI Zhen-GaoP. CHRISTIE
An incubation experiment was conducted to evaluate the potential for water contamination with sludge-derived organic substances and copper following land application of alkaline-stabilised sewage sludge. Twocontrasting sludge-amended soils were studied. Both soils were previously treated with urban and ruralalkaline biosolids separately at sludge application rates of 0, 30 and 120 t ha-1 fresh product. The air-driedsoil/sludge mixtures were wetted with distilled water, maintained at 40 % of water-holding capacity andequilibrated for three weeks at 4 ℃ before extraction. Subsamples were extracted with either distilled wateror 0.5 mol L-1 K2SO4 solution. The concentrations of organic C in the aqueous and chemical extractswere determined directly with a total organic carbon (TOC) analyser. The concentrations of Cu in the twoextracts were also determined by atomic absorption spectrophotometry The relationship between the twoextractable organic C fractions was examined, together with that between extractable organic C concentrationand extractable Cu concentration. Application of alkaline biosolids increased the concentrations of soil mobileorganic substances and Cu. The results are discussed in terms of a possible increase in the potential forleaching of sludge-derived organics and Cu in the sludge-amended soils.
A pot experiment was catried out to study alleviation of soil acidity and Al toxicity by applying analkaline-stabilised sewage sludge product (biosolids) to an acid clay sandy loam (pH 5.7) and a strongly acidsandy loam (pH 4.5). Barley (Hondeum vulgare L. cv. Forrester) was used as a test crop and was grownin the sewage sludge-amended (33.5 t sludge DM ha-1) and unamended soils. The results showed that thealka1ine biosloids increased soil pH from 5.7 to 6.9 for the clay sandy loam and from 4.5 to 6.0 for the sandyloam. The sludge product decreased KCl-extractable Al from 0.1 to 0.0 cmol kg-1 for the former soil andfrom 4.0 to 0.1 cmol kg-1 for the latter soil. As a result, barley plants grew much better and grain yieldincreased greatly in the amended treatments compared with the unamended controls. These observationsindicate that alkaline-stabilised biosolids can be used as a liming material for remedying Al phytotoxicity instrongly acid soils by increasing soil pH and lowering Al bioavailability.