Soil management influences physical properties and mainly the soil hydraulic functions. Their measurement becomes one of the research preferences in this branch of applied soil science. Tension disc and pressure ring infiltrometers have become very popular devices for the in situ estimates of soil surface hydraulic properties. Their use for measuring solute–water transfer parameters of soils is now well established too. A number of publications testify that both devices have been extensively used all around the world for different purposes. In this review, a short introduction is devoted to the background theory and some examples are given to show how the theory can be used to determine hydraulic conductivity and sorptivity from measured cumulative infiltration. The methods of analysis of cumulative infiltration are based either on quasi-analytical solutions of the flow equation for homogeneous soil profile or on inverse parameter estimation techniques from the numerical solution of flow equation whether the soil profile is homogeneous or not. The disc infiltrometer has also been shown as a suitable device for inferring parameters describing the water-borne transport of chemicals through near saturated soils. Associated with conservative tracers, it has been recognized as a promising tool for the determination of both hydraulic and solute transport properties as well as for other parameters such as mobile/immobile water content fraction or exchange coefficient. An emphasis is put here on some published studies performed in different soils and environmental conditions focusing on heterogeneous soil profiles (crusted soils) or structured cultivated soils (aggregated soils), either when local water transport process is studied or when field spatial variability is investigated. Some new research studies such as water–solute transfer in structured or swelling–shrinking soils and multi-interactive solute transport are emerging. A number of challenges still remain unresolved for both theory and practice for tension and pressure infiltrometers. They include questions on how to consider and characterize saturated–unsaturated preferential flow or preferential transport process (including hydrodynamic instabilities) induced by biological activity (e.g. capillary macropores, earthworm holes or root channels) by specific pedagogical conditions (e.g. cracking, crusting) and by soil management practices (i.e. conservation tillage).

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Field measurement of soil surface hydraulic properties by disc and ring infiltrometers: A review and recent developments

The increased use of trickle or drip irrigation is seen as one way of helping to improve the sustainability of irrigation systems around the world. However, soil water and solute transport properties and soil profile characteristics are often not adequately incorporated in the design and management of trickle systems. In this paper, we describe results of a simulation study designed to highlight the impacts of soil properties on water and solute transport from buried trickle emitters. The analysis addresses the influence of soil hydraulic properties, soil layering, trickle discharge rate, irrigation frequency, and timing of nutrient application on wetting patterns and solute distribution. We show that (1) trickle irrigation can improve plant water availability in medium and low permeability fine-textured soils, providing that design and management are adapted to account for their soil hydraulic properties, (2) in highly permeable coarse-textured soils, water and nutrients move quickly downwards from the emitter, making it difficult to wet the near surface zone if emitters are buried too deep, and (3) changing the fertigation strategy for highly permeable coarse-textured soils to apply nutrients at the beginning of an irrigation cycle can maintain larger amounts of nutrient near to and above the emitter, thereby making them less susceptible to leaching losses. The results demonstrate the need to account for differences in soil hydraulic properties and solute transport when designing irrigation and fertigation management strategies. Failure to do this will result in inefficient systems and lost opportunities for reducing the negative environmental impacts of irrigation.

Analysis of soil wetting and solute transport in subsurface trickle irrigation

In this paper we propose a generalization of multiscale finite element methods (Ms-FEM) to nonlinear problems. We study the convergence of the proposed method for nonlinear elliptic equations and propose an oversampling technique. Numerical examples demonstrate that the over-sampling technique greatly reduces the error. The application of MsFEM to porous media flows is considered. Finally, we describe further generalizations of MsFEM to nonlinear time-dependent equations and discuss the convergence of the method for various kinds of heterogeneities.

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Multiscale Finite Element Methods for Nonlinear Problems and Their Applications

Tension disk infiltrometer experiments are generally conducted until apparent steady state is reached because most of the methods of analysis are based on Wooding's solution for steady state flux. However, the time necessary to reach steady state may be a penalizing aspect for soils with low permeability and the information contained in the transient stages is not utilized. Moreover, these methods assume homogeneous soil and a uniform initial water content, which may be unrealistic when a large volume of soil is sampled. In this series, we propose and compare several new methods of analysis that are based on the transient stage of axisymmetric infiltration. In the first part, we show that a two-parameter equation-one term linear in square root of time and one term linear in time-adequately describes the transient flow from the disk infiltrometer for both simulated and laboratory tests. The technique used for the determination of the two coefficients must meet two criteria; it must verify the validity of the two-term equation throughout the duration of the experiment, and it must account for the early-time perturbation that is induced by the sand-contact layer placed between the disk and the soil. We show that the best technique consists in linearizing the data by differentiating cumulative infiltration with respect to the square root of time. Direct nonlinear fitting on cumulative infiltration or infiltration flux is likely to lead to unacceptable errors, either because of the undetected invalidity of the two-parameter equation or arising from the influence of the contact layer.

Transient flow from tension infiltrometers : I. The two-parameter equation

Designing trickle irrigation systems involves the selection of a proper combination of trickle discharge rate, spacing between emitters, diameter and length of the lateral system for any given set of soil, crop and climatic conditions. Trickle irrigation is treated as transient and steady axisymmetric infiltration processes. An existing numerical solution to nonsteady state infiltration is used to quantify the effect of soil hydraulic properties and trickle discharge rates on emitter spacing (Fig. 2). The results of the analysis suggest the possibility of controlling the wetted volume of a soil by regulating the emitter discharge according to soil properties (Figs. 3 and 4). The surface distribution of a transformed soil water content (or pressure) function (Fig. 5) is derived from a linearized solution to steady infiltration. The analysis of steady and non-steady infiltration is employed to estimate the spacing between emitters as a function of discharge and water pressure conditions between emitters using hydraulic soil data (Fig. 6). Hydraulic conductivity parameters are given for 17 different soils (Table 1) to be used for design purposes. Theoretical analysis of soil water is combined with hydraulic principles to derive lateral diameter and length for engineering design requirements.

Analysis of trickle irrigation with application to design problems

Water flow from strip and disc surface sources is analyzed using an approach similar to previous investigations with line and point sources. A line of closely spaced trickle irrigation emitters often wets a surface strip of finite width; similarly, for a single emitter the surface wetted pattern is a disc. Lines of equal matric flux potential are wider and more shallow for these sources than wetting patterns for the line and point. The moisture regime is independent of the source shape and depends only on the total flow rate for regions beyond approximately two times the strip width or disc radius.

D. O. Lomen

Papers

Time-dependent Linearized Infiltration: III. Strip and Disc Sources