Sewage sludge processing determines its impact on soil microbial community structure and function

Mattana S., Petrovicova B., Landi L., Gelsomino A., Cortes P., Ortiz O., Renella G. (2014) Sewage sludge processing determines its impact on soil microbial community structure and function. Applied Soil Ecology. 75: 150-161.
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Doi: 10.1016/j.apsoil.2013.11.007

Resum:

Composting and thermal drying are amongst the most commonly used post-digestion processes for allowing sanitation and biological stabilization of sewage sludge from municipal treatment plants, and making it suitable as soil conditioner for use in agriculture. To assess the impact of sludge-derived materials on soil microbial properties, fresh (LAF), composted (LAC) and thermally dried (LAT) sludge fractions, each resulting from a different post-treatment process of a same aerobically digested sewage sludge, were added at 1% (w/w) application rate on two contrasting (a loam and a loamy sand) soils and incubated under laboratory conditions for 28 days. Soil respiration, microbial ATP content, hydrolytic activities and arginine ammonification rate were monitored throughout the incubation period. Results showed that soil biochemical variables, including the metabolic quotient (qCO2), were markedly stimulated after sludge application, and the magnitude of this stimulatory effect was dependent on sludge type (precisely LAT>LAF>LAC), but not on soil type. This effect was related to the content of stable organic matter, which was lower in LAT. Genetic fingerprinting by PCR-DGGE revealed that compositional shifts of soil bacterial and, at greater extent, actinobacterial communities were responsive to the amendment with a differing sludge fraction. The observed time-dependent changes in the DGGE profiles of amended soils reflected the microbial turnover dependent on the sludge nutrient input, whereas no indications of adverse effects of sludge-borne contaminants were noted. Our findings indicate that composting rather thermal drying can represent a more appropriate post-digestion process to make sewage sludge suitable for use as soil conditioner in agriculture. © 2013 Elsevier B.V.

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Can organic amendments be useful in transforming a mediterranean shrubland into a dehesa?

Tarrason D., Ojeda G., Ortiz O., Alcaniz J.M. (2014) Can organic amendments be useful in transforming a mediterranean shrubland into a dehesa?. Restoration Ecology. 22: 486-494.
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Doi: 10.1111/rec.12092

Resum:

Transforming a shrubland into a dehesa system may be useful for recovering certain productive and regulatory functions of ecosystems such as grazing potential, soil erosion control, and also for reducing the risk of wildfire. However, the productivity of the herbaceous cover and tree development in the transformed system may be limited by soil fertility, especially after wildfire events. Previous studies have shown that adequate doses of sewage sludge may improve soil fertility and facilitate plant recovery, but few studies have focused on plant biodiversity assessment. Here, we compare the effects of sewage sludge that has undergone different post-treatments (dewatering, composting, or thermal drying) as a soil amendment used to transform a fire-affected shrubland into a dehesa, on tree growth and pasture composition (vegetation cover, species richness, and diversity). In the short term, sewage sludge causes changes in both pasture cover and tree growth. Although no major differences in vegetation species richness and composition have been detected, fertilization using sewage sludge was shown to modify the functional diversity of the vegetation community. Rapid replacement of shrubs by herbaceous cover and ruderal plants (e.g. Bromus hordeaceus and Leontodon taraxacoides) and of the three grass species sown (Festuca arundinacea, Lolium perenne, and Dactylis glomerata) was observed, whereas N-fixing species (leguminous) tended to be more abundant in nonfertilized soils and soils amended with composted sludge. These results indicate that sewage sludge modifies the functionality of vegetation when applied to soils, and that the response varies according to the treatment that the sludge has undergone. © 2014 Society for Ecological Restoration.

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