Ojeda G., Alcañiz J.M., Le Bissonnais Y. (2008) Differences in aggregate stability due to various sewage sludge treatments on a Mediterranean calcareous soil. Agriculture, Ecosystems and Environment. 125: 48-56.EnllaçDoi: 10.1016/j.agee.2007.11.005
Three types of sewage sludge from the same wastewater treatment plant but processed in different ways (composted, fresh and thermally dried) were applied in doses equivalent to approximately 10 Mg of dry matter per hectare to the surface of a loamy soil in order to improve its physical condition. The effect of this organic amendment on the structural stability of the soil was measured using a procedure which explores three types of disaggregation mechanisms: slaking, mechanical breakdown by raindrop impact and disaggregation induced by differential swelling. Two years after the surface application of the sludge, the treated soils have a higher organic carbon and hydrolyzable carbohydrate content and greater structural stability than the control treatment. It was observed that while all three types of sludge reduced soil disaggregation due to differential swelling and splash, only the treatments with composted and thermally dried sludge were effective in reducing slaking. © 2007 Elsevier B.V. All rights reserved.
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.
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