ANALYZING PROBLEMS IN DESCRIBING FIELD AND LABORATORY MEASURED SOIL HYDRAULIC-PROPERTIES

Citation
G. Wessolek et al., ANALYZING PROBLEMS IN DESCRIBING FIELD AND LABORATORY MEASURED SOIL HYDRAULIC-PROPERTIES, Geoderma, 64(1-2), 1994, pp. 93-110
Citations number
31
Categorie Soggetti
Agriculture Soil Science
Journal title
ISSN journal
00167061
Volume
64
Issue
1-2
Year of publication
1994
Pages
93 - 110
Database
ISI
SICI code
0016-7061(1994)64:1-2<93:APIDFA>2.0.ZU;2-B
Abstract
Accurate in situ determination of unsaturated soil hydraulic propertie s is often not feasible because of natural variability of most field s oils, and because of instrumental limitations. Therefore the soil hydr aulic properties are often measured in the laboratory, or derived by c omputer models using simple standard laboratory methods. This paper an alyses problems in describing field hydraulic properties of a Ap horiz on of a silty loam, basing on data from different laboratory methods: (i) A standard pressure plate apparatus and (ii) a constant-head perme ameter were used to measure the static retention characteristics and t he saturated hydraulic conductivity independently. (iii) An instantane ous profile method was applied to measure water retention and conducti vity simultanously. Relatively new technics involving ''undisturbed'' soil samples instrumented with mini tensiometers and Time Domain Refle ctometry (TDR) mini probes characterise the experiment. The models by Mualem and van Genuchten (MvG) were used to describe the soil hydrauli c functions. The different laboratory results were then compared with the hydraulic field properties measured in instantaneous profile manne r. The laboratory method allows a high spatial and temporal resolution ; this facilitates an investigation of some of the assumptions made, w hen fitting the MVG models to hydraulic data. A reasonably good descri ption of the hydraulic data was obtained when setting the residual wat er content, theta(I), to 0 and the pore connectivity factor, l, to 0.5 because theta(I), and I were not sensitive. However, a poor fit resul ted when the saturated water content, theta(s), was equated to the por osity, and the saturated hydraulic conductivity, k(s), to its independ ently measured value. Values for theta(s) and k(s) derived from field measurements were somewhat higher than those obtained from laboratory samples. To demonstrate the influence of the different input data on a water balance, the cumulative drainage from an initially saturated so il column was simulated with different sets of hydraulic parameters es timated from field and laboratory data. Parameters derived from the la boratory results consistently yielded lower predictions of cumulative drainage compared to hydraulic parameters derived from field measureme nts. The differences were relatively small when an initial water conte nt corresponding to 60 cm suction (field capacity) was used.