P. A. Londra

Effects of compost produced from town wastes and sewage sludge on the physical properties of a loamy and a clay soil

Abstract Organic fertilizer produced by composting 62% town wastes, 21% sewage sludge and 17% sawdust by volume, was applied at the rates of 0 (control), 75, 150 and 300 m3 ha−1 to loamy and clay soils, in order to investigate its potential for soil improvement. The experiments were conducted in areas characterised by a semi-arid climate. The chemical properties of the soils were affected directly by the amendment compost. The physical properties of the amended soils were improved in all cases as far as the saturated and unsaturated hydraulic conductivity, water retention capacity, bulk density, total porosity, pore size distribution, soil resistance to penetration, aggregation and aggregate stability, were concerned. In most of the cases the improvements were proportional to the application rates of the compost and they were greater in the loamy soil than in the clay soil.

Effect of tillage practices on the hydraulic properties of a loamy soil

AbstractThe knowledge of soil hydraulic properties is essential for modeling the water flow in unsaturated porous media for hydrological applications and agricultural water management. Long-term tillage practices have been shown to affect the hydraulic properties of soil. In this study, a field experiment was conducted to evaluate the effect of roto-tillage and no-tillage practices on the hydraulic properties of a bare loam soil. Two field plots were used with different tillage practices. In the first one, the field has been in roto-tillage for three years and in the other in continuous no-tillage for two years. From the hydraulic properties determined, water retention curves indicated that the water retention capacity was greater in tilled than in no-tilled (NT) soil. Both soil–water diffusivity and hydraulic conductivity values were greater in tilled than in NT soil at relatively low to moderate water contents, and lower in tilled than in NT soil at relatively high water contents—near saturation. The hy...

Rapid Graphical Detection of Weakness Problems in Numerical Simulation Infiltration Models Using a Linearized Form Equation

Recently, Valiantzas proposed a new two-parameter vertical infiltration equation that can be transformed to a linearized-form equation that essentially states that the shape of the cumulative infiltration data, when presented in the form of (i2/t) versus i, is linear. In this paper, the presentation of the numerical data to the Valiantzas linearized-form equation is proposed as an additional criterion to detect easily and rapidly possible errors of the numerical solutions and eventually to choose the best spatial discretization for a simulated infiltration event that is used as setup parameter to the numerical infiltration models. Numerical data and analytical solutions were used to validate the proposed method.

Modified Form of the Extended Kostiakov Equation Including Various Initial and Boundary Conditions

The extended Kostiakov equation is intensively used in surface irrigation applications. Traditionally, the extended Kostiakov infiltration formula is calibrated for specific field conditions. However, there is a dependence of the extended Kostiakov coefficients on both initial and boundary conditions. In this paper, a new simplified methodology is developed to account extended Kostiakov κ variation for these effects. The purely empirical extended Kostiakov equation is transformed to a form of a modified version of the classical Philip two-term equation. This modification relates a physical parameter, the soil sorptivity S, with the purely empirical coefficient κ of the extended Kostiakov formula. Then, the variation of the sorptivity S for various water levels and initial water contents is given theoretically by a simple algebraic equation. The proposed correction was compared with numerical infiltration data with varying initial (water content) and boundary conditions (ponding depth) for two contrasting soils. Results indicate that the corrected infiltration curves converge well with the simulated ones.

Evaluation of porous medium hydraulic properties using experimental methods and RETC code

ABSTRACT Two experimental procedures were used to determine both hydraulic properties, soil water retention θ(h) curve and unsaturated hydraulic conductivity K(θ), of a sand sample. Knowledge of hydraulic properties is essential, since they generally control soil water dynamics. A steady-state laboratory method was used for the simultaneous determination of θ(h) and K(θ). A one-step outflow method was used for the determination of diffusivity D(θ) and subsequently K(θ) from soil water retention data which were measured independently on the same sample and using the same apparatus. The comparison of K(θ) measured values from the above-mentioned methods showed very good agreement of the results. Also, the comparison between the experimental K(θ) and θ(h) functions and the predictions obtained using retention curve (RETC) code by simultaneous fit of experimental soil water retention and hydraulic conductivity data from outflow data, assuming the Mualem-van Genuchten model, showed very good agreement. It is noted that the main disadvantage of the one-step outflow method is the weakness to predict K(θ) values near saturation. This disadvantage could be overcome using RETC code with the above procedures, since the K(θ) values between the predictive approach and the steady-state method were similar.

Investigation of the Relationship between Three- and One-Dimensional Infiltration Using a Mini Disc Infiltrometer

Disc infiltrometer experiments were conducted in the laboratory on two disturbed soils, a loam and a silty clay loam soil, in order to investigate the relationship between three- and one-dimensional infiltration using the proposed equation of Smettem et al. A mini disc infiltrometer of a radius of 45 mm with suction ranged from −5 mm to −70 mm was used. Three- and one-dimensional infiltration tests were performed on repacked cores by applying pressure heads −70, −40 and −10 mm for loam soil, and −30 and −10 mm for silty clay loam soil. Analysis of the results showed that the difference between the three- and one-dimensional infiltration is linear with time confirming the equation of Smettem et al. [1]. Also, this difference is used to calculate the value of an additional infiltration parameter.