Wetting process and soil water retention of a minesoil amended with composted and thermally dried sludges

Ojeda G., Mattana S., Alcañiz J.M., Marando G., Bonmatí M., Woche S.K., Bachmann J. (2010) Wetting process and soil water retention of a minesoil amended with composted and thermally dried sludges. Geoderma. 156: 399-409.
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Doi: 10.1016/j.geoderma.2010.03.011

Resum:

Composting or thermally-drying sludges are becoming commonly used in soil rehabilitation of degraded land. Sludge amendments increase soil organic matter, but can reduce soil wettability due to hydrophobic compounds. The main objective of this study is to analyse how composted and thermally dried sludges influence soil wettability and water retention properties of a minesoil obtained from limestone extraction during quarrying rehabilitation activities. Three composted (Blanes, Manresa and Vilaseca) and three thermally dried (Besós, Mataró and Sabadell) municipal sludges from different wastewater plants of medium-sized towns located in Catalonia (NE Spain) were mixed with a minesoil and filled into lysimeters The minesoil water retention curves and, the time required for their measurement were analyzed together with various soil key parameters. Throughout the wetting process, three characteristic points of the water retention curve were identified: (i) the air soil dryness point corresponding to a soil suction of - 25 MPa, (ii) the critical point where high suction regime changes to low suction regime, located around - 6 MPa and (iii) the wilting point, corresponding to a soil suction of - 1.5 MPa. One month after sludge amendments (S1), two composted sludges increased the vapour wetting time corresponding to wilting point (twp) of minesoil, while 1 year after sludge amendments (S2) two thermally dried sludges decreased twp. On the other hand, all composted sludges and one thermally dried sludge increased minesoil water retention corresponding to wilting point (wwp) at sampling one (S1), while at sampling two (S2) similar effects were observed except in one composted sludge treatment. Regarding to soil biophysical properties, the addition of composted and thermally dried sludges to minesoil increased total organic carbon, soil-water contact angle, microbial biomass, pH and electrical conductivity at both experimental time scales (S1 and S2), while extractable carbohydrates was only modified at S1. The sludge effects on soil wetting properties and biophysical parameters were dependent on sewage sludge origin and the type of post-treatment. Increases in total organic carbon, extractable carbohydrates, contact angle, microbial biomass or electrical conductivity and decreases in pH corresponded with increases in twp and wwp. It was observed that under similar conditions of water vapour adsorption, minesoil amended with composted sludge could have more difficulties to overcome the permanent wilting point under wetting process. © 2010 Elsevier B.V. All rights reserved.

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