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.EnllaçDoi: 10.1111/rec.12092
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.
Tarrasón D, Ojeda G, Ortiz O, Alcañiz JM (2010) Effects of Different Types of Sludge on Soil Microbial Properties: A Field Experiment on Degraded Mediterranean Soils. Pedosphere 20: 681-691.
Tarrasón D., Ojeda G., Ortiz O., Alcañiz J.M. (2008) Differences on nitrogen availability in a soil amended with fresh, composted and thermally-dried sewage sludge. Bioresource Technology. 99: 252-259.EnllaçDoi: 10.1016/j.biortech.2006.12.023
Anaerobically-digested sludge called fresh sludge (F), composted sludge (C) and thermally-drying sludge (T), all from the same batch, were applied to the surface of a calcareous Udic Calciustept with loamy texture. Dosage equivalent was 10 t ha-1 of dry matter. The concentration of mineral nitrogen (ammonium and nitrate) in the soil was measured in order to estimate the effects of the post-treatments to which the different kinds of sewage sludge are subjected in relation to the availability of N in the surface layer of the soil. The most significant differences in NH4-N and NO3-N concentrations due to the transformation of the organic matter were observed during the first three weeks following soil amendment. Thermally-dried and composted sludge initially displayed higher concentrations of ammonium and nitrate in soil. Five months after the amendment, soil applied with fresh sludge showed the highest concentrations of NH4-N and NO3-N (6.1 and 36.6 mg kg-1, respectively). It is clear that the processes of composting and thermal-drying influence the bioavailability of nitrogen from the different types of sewage sludge. © 2007 Elsevier Ltd. All rights reserved.
Tarrasón D., Ortiz O., Alcañiz J.M. (2007) A multi-criteria evaluation of organic amendments used to transform an unproductive shrubland into a Mediterranean dehesa. Journal of Environmental Management. 82: 446-456.EnllaçDoi: 10.1016/j.jenvman.2006.01.002
Environmental and health problems associated with the use of digested sewage sludge hinder its application and encourage the introduction of additional treatments such as composting and thermal drying. The aim of this paper is to assess the possibility of using three different types of sewage sludge (digested, composted and thermally dried) to improve soil fertility and enhance the transformation of an unproductive shrub land into a Mediterranean dehesa for grazing purposes and also to reduce wildfire risk. In total, 10 t ha-1 of dry matter of three types of sewage sludge were spread on the soil surface of 4×5 m field plots, and then seeded with a mixture of grasses. Effects on soil fertility and plant growth were monitored over 2 years. The results show that all three types of sludge application had a significant effect on vegetation cover, herbaceous biomass (2767.7±716.1 and 1735.0±299.7 kg ha-1 for digested sludge amended and control plots, respectively) and tree growth (0.41±0.108 cm year-1 on amended trees, 14.6% more than control trees). This study proposes the use of multi-criteria analysis to identify the most suitable fertilization alternatives and to assist in the decision-making process of sludge recycling. Because of the high degree of uncertainty and conflicting objectives associated with these decisions, multi-criteria evaluation tools make a valuable contribution to decision-making processes concerning sewage sludge applications. According to multi-criteria results, the composted sludge alternative is the most suitable. This is because all the objectives are achieved: an improvement in the properties and functions of the soil with a positive vegetation response as well as minimal economic cost and risk of toxicity. © 2006 Elsevier Ltd. All rights reserved.
Ojeda G., Tarrasón D., Ortiz O., Alcañiz J.M. (2006) Nitrogen losses in runoff waters from a loamy soil treated with sewage sludge. Agriculture, Ecosystems and Environment. 117: 49-56.EnllaçDoi: 10.1016/j.agee.2006.02.017
Sludge from the same waste-water treatment plant, processed in different ways, was applied superficially to plots of a soil developed on marls (Udic calciustept) at doses equivalent to 10 t ha-1 of dry matter. The concentration of mineral nitrogen (ammonium, nitrate) in runoff waters was measured to assess the effects of composting and thermally drying of sludge on the pollution of surface waters. Significant differences of NH4-N and NO3-N concentration in both runoff waters and soil only appeared during the first five runoff events after sludge application. Thereafter, runoff volume decreased remarkably, possibly due to vegetation growth. The treatment with composted sludge contributes mainly to NO3-N runoff, whereas the NH4-N was predominant in runoff from plots of thermally-dried sludge. The treatment with fresh sludge provided NH4-N and NO3-N to surface runoff in similar amounts. The electrical conductivity of the runoff was not greatly affected by the surface application of the sewage sludges. © 2006 Elsevier B.V. All rights reserved.
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