The addition of clay to lime-amended biosolids has been proposed as a soil amendment (LaBCA (R)) for remediating acidic-sandy soil. We investigated whether the presence of clay in LaBCA (R) altered soil microbial processes over a 30-week period. Aerobic-incubation and CO2 respiration assays were used to monitor water repellence and chemical and microbiological properties of amended soil. Dry LaBCA (R) was applied at equivalent wet weight of 50, 100 and 150 t ha(-1). In addition, dry components of LaBCA (R) (lime, clay, lime + clay (LAC) and lime + biosolids (LAB)) were applied separately at rates equivalent to their fractions within LaBCA (R). Inclusion of clay in LaBCA (R) was effective in eliminating water repellence at all application rates. Inclusion of clay in LaBCA (R) decreased nitrogen (N) release from the biosolids (by 58 ), even at 50 t ha(-1), but only during the first 2 weeks of incubation. LaBCA (R) consistently decreased soil microbial respiration compared with LAB alone when applied at 150 t ha(-1) thereby protecting organic matter decomposition. There was no significant N release with lime and clay amendment alone or in combination (LAC) in the absence of the biosolids. There may be a complex interaction between clay, lime and organic matter, but each may have had a role in altering N release from biosolids at different times during the 30-week incubation. Addition of clay to LAB increased its effectiveness in remediating this water-repellent, acidic-sandy soil and prolonged the N release from the biosolids following soil amendment
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