Fractal analysis of soil water hysteresis as influenced by sewage sludge application

Ojeda G., Perfect E., Alcañiz J.M., Ortiz O. (2006) Fractal analysis of soil water hysteresis as influenced by sewage sludge application. Geoderma. 134: 386-401.
Enllaç
Doi: 10.1016/j.geoderma.2006.03.011

Resum:

The impact of three types of surface applied sewage sludge from the same lot (fresh, composted, and thermally dried) on the water retention properties of a loam soil (Udic Calciustept) and a loamy sand soil (Typic Haplustalf) from central Catalonia (NE Spain) was investigated using fractal analysis. First, we proposed a composite fractal model that covers both the low and high suction regimes. This model has four fitting parameters: D1 (the pore-solid fractal dimension), D2 (the surface fractal dimension), A1 (a compound parameter that includes D1, the density of water, bulk density, particle density, and the air/water displacement suction), and A2 (a compound parameter that includes D2, and the critical suction and water content separating the low and high suction regimes). This model was fitted to the main wetting and drying branches of soil water retention curves obtained from small-disturbed samples using the chilled mirror dew point method. The equation fitted the data extremely well with adjusted R2 values ≥ 0.99 (p < 0.0001). Analysis of variance (ANOVA) was performed on the resulting parameter estimates. Few significant effects were observed for the loamy sand soil. In contrast, all of the model parameters, except D1, were significantly affected by hysteresis and/or the sludge treatments for the loam soil. Values of A1 and A2 from the main drying branch were significantly higher than corresponding estimates from the wetting branch. This trend was reversed for D2, indicating that pore surfaces are smoother after wetting, as compared to initially dry surfaces. The fresh, composted and thermally dried sludge treatments all significantly increased the A1 parameter relative to the untreated loam soil, possibly by decreasing bulk density. The fresh and thermally dried sludge treatments also significantly increased the A2 parameter. All three sludge types increased D2 relative to the control when this parameter was determined from the main wetting branch of the water retention curve. In contrast, D2 estimated from the main drying branch was not influenced by any of the sludge treatments. These analyses indicate that the effects of sewage sludge on hysteresis of the soil water retention curve were still present 2 years after surface application in the case of the loam soil. © 2006 Elsevier B.V. All rights reserved.

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Nitrogen losses in runoff waters from a loamy soil treated with sewage sludge

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.
Enllaç
Doi: 10.1016/j.agee.2006.02.017

Resum:

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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