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

Soil management influences physical properties and mainly the soil hydrauli c functions. Their measurement becomes one of the research preferences in t his branch of applied soil science. Tension disc and pressure ring infiltro meters have become very popular devices for the in situ estimates of soil s urface hydraulic properties. Their use for measuring solute-water transfer parameters of soils is now well established too. A number of publications t estify that both devices have been extensively used all around the world fo r different purposes. In this review, a short introduction is devoted to th e background theory and some examples are given to show how the theory can be used to determine hydraulic conductivity and sorptivity from measured cu mulative infiltration. The methods of analysis of cumulative infiltration a re based either on quasi-analytical solutions of the flow equation for homo geneous soil profile or on inverse parameter estimation techniques from the numerical solution of flow equation whether the soil profile is homogeneou s or not. The disc infiltrometer has also been shown as a suitable device f or inferring parameters describing the water-borne transport of chemicals t hrough near saturated soils. Associated with conservative tracers, it has b een recognized as a promising tool for the determination of both hydraulic and solute transport properties as well as for other parameters such as mob ile/immobile water content: fraction or exchange coefficient. An emphasis i s put here on some published studies performed in different soils and envir onmental 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 investig ated. Some new research studies such as water-solute transfer in structured or swelling-shrinking soils and multi-interactive solute transport are eme rging. A number of challenges still remain unresolved for both theory and p ractice for tension and pressure infiltrometers. They include questions on how to consider and characterize saturated-unsaturated preferential Row or preferential transport process (including hydrodynamic instabilities) induc ed by biological activity (e.g. capillary macropores, earthworm holes or ro ot channels) by specific pedagogical conditions (e.g. cracking, crusting) a nd by soil management practices (i.e. conservation tillage). (C) 2000 Elsev ier Science B.V. All rights reserved.