Predicting water balance in a sandy soil: model sensitivity to the variability of measured saturated and near saturated hydraulic properties
Y. M. Oliver A B D and K. R. J. Smettem CA CSIRO Sustainable Ecosystems, Private Bag 5 PO, Wembley, WA 6913, Australia.
B Formerly School of Earth and Geographical Sciences, Faculty of Natural and Agricultural Science, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.
C Centre for Water Research, The University of Western Australia, 35 Stirling Hwy Crawley, WA 6009, Australia.
D Corresponding author. Email: yvette.oliver@csiro.au
Australian Journal of Soil Research 43(1) 87-96 https://doi.org/10.1071/SR03146
Submitted: 8 October 2003 Accepted: 24 September 2004 Published: 14 February 2005
Abstract
Water balance modelling based on Richards’ equation requires accurate description of the soils’ hydraulic parameters. Unfortunately, these parameters vary spatially and temporally as well as between measurement techniques. For most field modelling exercises, the hydraulic parameters are obtained from a small number of measurements or predicted from soil properties using pedo-transfer functions. The effect of different measurement techniques on the description of soil hydraulic parameters has been the subject of many studies but the effect of the variability of the hydraulic parameters on the predicted water balance has not been widely investigated.
In this study we compared the hydraulic parameters obtained solely from laboratory measurements with those obtained from a rapid wet end field measurement technique, augmented by dry end laboratory data. The water balance was modelled using the laboratory and field hydraulic parameter sets and compared to field water contents measured by time domain reflectometry (TDR). In a sandy soil, we found the total profile water content to be well modelled by both hydraulic parameter datasets, but the water content at a specific depth was less well predicted using either of the measured parameter sets. The water content at a specific depth was under-predicted prior to the rainfall event and over-predicted after the rainfall, regardless of whether the hydraulic parameters were obtained from laboratory or field measurements. Generally, the hydraulic parameters that were obtained from the field measurements gave a closer fit to the measured TDR water contents.
The sensitivity of the modelled water balance to changes in the hydraulic parameters within the observed range of parameter values was also investigated. Parameter percentage coefficient of variation within measurement techniques ranged from 60% for air entry, he; 19% for residual water content, θr; 5% for slope of the water retention curve, n; and 7% for saturated water content, θs. The percentage differences between the parameters obtained from the laboratory and field measurement techniques for the topsoil and subsoil respectively were 47% and 50% for he, 100% for θr, 28% and 40% for n, and –14.4% and 4.0% for θs.
Modelling water content changes at a particular depth in the sandy soil was found to be most influenced by variations in θs, and n. Predicted water contents were also affected by the θr but less influenced by the saturated hydraulic conductivity, Ks. The he was the least influential parameter but also the most variable. This suggests that measurement of θs, related to bulk density changes caused by tillage, wheel compaction, and consolidation, is required for water balance studies. Generally, n had small variability between measurements at a particular depth, which is promising for the use of pedo-transfer functions related to soil texture.
Additional keywords: laboratory and field, hydraulic parameter measurement, water balance modelling, SWIM.
Acknowledgments
This research was funded by the Grains Research Development Corporation. Thanks go to Mr Michael Brennan (Ninnan Farms) who generously loaned the land, to Ian Fillery for the field site management, and to Peter Ross for updating the SWIM model into excel.
Addiscott TM, Whitmore AP
(1987) Computer simulation of changes in soil mineral nitrogen and crop nitrogen during autumn, winter and spring. Journal of Agricultural Science 109, 141–157.
Anderson GC,
Fillery IRP,
Dolling PJ, Asseng S
(1998a) Nitrogen and water flow under pasture-wheat and wheat-lupin rotations in deep sands in Western Australia 1. Nitrogen fixation in legumes, net N mineralisation, and utilisation of soil derived nitrogen. Australian Journal of Agricultural Research 49, 329–343.
| Crossref | GoogleScholarGoogle Scholar |
Anderson GC,
Fillery IRP,
Dunin FX,
Dolling PJ, Asseng S
(1998b) Nitrogen and water flow under pasture-wheat and wheat-lupin rotations in deep sands in Western Australia 2. Drainage and nitrate leaching. Australian Journal of Soil Research 49, 345–361.
Bork HR, Diekrugger B
(1990) Scale and regionalization problems in soil science. Transactions of the 14th International Congress of Soil Science
, 178–181.
Brooks RH, Corey AT
(1964) Hydraulic properties of porous media. Hydrology Papers No. 3. Colorado State University, Fort Collins, USA.
Burdine NT
(1953) Relative permeability calculations from pore-size distribution data. Petrology Transactions AIME 198, 71–77.
Campbell GS
(1974) A simple method of determining unsaturated hydraulic conductivity from moisture retention data. Soil Science 117, 311–315.
Celia MA,
Bouloutas ET, Zarba RL
(1990) A general mass-conservation numerical solution for the unsaturated flow equation. Water Resources Research 26, 1483–1496.
| Crossref | GoogleScholarGoogle Scholar |
Field JA,
Parker JC, Powell NL
(1985) Comparison of field and laboratory measured and predicted hydraulic properties of soil with macropores. Soil Science 138, 385–396.
Fuentes C,
Haverkamp R, Parlange JY
(1992) Parameter constraints on closed-form soil water relationships. Journal of Hydrology 134, 117–142.
| Crossref | GoogleScholarGoogle Scholar |
van Genuchten MTh
(1980) A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal 44, 892–898.
van Genuchten MTh, Leij FJ, Yates SR
(1991) The RETC code for quantifying the hydraulic functions of unsaturated soils. EPA/600/S2-91/065. (Environmental Protection Agency, Research and Development: Springfield, VA).
Gregory PJ,
Ross P,
Eastham J, Micin S
(1995) Use of time domain reflectometry (TDR) to measure soil water content in sandy soils. Australian Journal of Soil Research 33, 265–276.
Hart GL,
Lowery B,
McSweeney K, Fermanich KJ
(1994) In situ characterization of hydrologic properties of Sparta sands: relation to solute movement. Geoderma 64, 41–55.
| Crossref | GoogleScholarGoogle Scholar |
Isbell, RF (1996).
Loague K, Green RE
(1991) Statistical and graphical methods for evaluating solute transport models: Overview and application. Journal of Contaminant Hydrology 7, 51–73.
| Crossref | GoogleScholarGoogle Scholar |
Mallants D,
Jacques D,
Tseng PH,
van Genuchten MTh, Feyen J
(1997) Comparison of Three Hydraulic Property Measurement Methods. Journal of Hydrology 199, 295–318.
| Crossref | GoogleScholarGoogle Scholar |
Mallants D,
Tseng PH,
Vanclooster M, Feyen J
(1998) Predicted Drainage For a Sandy Loam Soil – Sensitivity to Hydraulic Property Description. Journal of Hydrology 206, 136–148.
| Crossref | GoogleScholarGoogle Scholar |
Marion JM,
Rolston DE,
Kavvas ML, Biggar JW
(1994) Evaluation of methods for determining soil-water retentivity and unsaturated hydraulic conductivity. Soil Science 158, 1–13.
Marquardt DW
(1963) An algorithm for least squares estimation of nonlinear parameters. Journal of the Society for Industrial and Applied Mathematics. 11, 431–441.
McArthur, WM (1991).
Northcote, KH (1979).
Pachepsky Y,
Rawls WJ, Gimenez D
(2001) Comparison of soil water retention at field and laboratory scales. Soil Science Society of America Journal 65, 460–462.
Paige GB, Hillel D
(1993) Comparison of three methods for assessing soil hydraulic properties. Soil Science 155, 175–189.
Parkes ME, Waters PA
(1980) Comparison of measured and estimated unsaturated hydraulic conductivity. Water Resources Research 16, 749–754.
Piggott JH, Cawlfield JD
(1996) Probabilistic Sensitivity Analysis For One-Dimensional Contaminant Transport in the Vadose Zone. Journal of Contaminant Hydrology 24, 97–115.
| Crossref | GoogleScholarGoogle Scholar |
Rawls WJ,
Brakensiek DL, Saxton KE
(1982) Estimation of soil water properties. Transactions of the American Society of Agricultural Engineers 25, 1316–1320.
Reynolds WD, Elrick DE
(1990) Ponded infiltration from a single ring: I. Analysis of steady flow. Soil Science Society of America Journal 54, 1233–1241.
Ross PJ
(1990) SWIM—a simulation model for Soil Water Infiltration and Movement. v1.1. (CSIRO: Townsville, QLD).
Ross PJ
(1997) SWIMv1. 1—Soil water Infiltration and Management. Excel Version.
Simunek J,
van Genuchten MTh,
Gribb MM, Hopmans JW
(1998) Parameter Estimation of Unsaturated Soil Hydraulic Properties From Transient Flow Processes. Soil and Tillage Research 47, 27–36.
| Crossref | GoogleScholarGoogle Scholar |
Smettem KRJ,
Oliver YM,
Heng LK,
Bristow KL, Ford EJ
(1999) Obtaining soil hydraulic properties for water balance and leaching models from survey data. 1. Water retention. Australian Journal of Agricultural Research 50, 283–289.
Soil Survey Staff (1987).
Tseng P, Jury WA
(1993) Simulation of field measurement of hydraulic conductivity in unsaturated heterogeneous soil. Water Resources Research 29, 2087–2099.
| Crossref | GoogleScholarGoogle Scholar |
Willmott CJ,
Ackleson SG,
Davis RE,
Feddema JJ,
Klink KM,
Legates DR,
O'Donnell J, Rowe CM
(1985) Statistics for the evaluation and comparison of models. Journal of Geophysical Research 90, 8995–9005.
Wu L,
Allmaras RR,
Lamb JB, Johnson KE
(1996) Model Sensitivity to Measured and Estimated Hydraulic Properties of a Zimmerman Fine Sand. Soil Science Society of America Journal 60, 1283–1290.
