Soil Physics [Link to My Web Courses]
Soil-Water and Plant Relations [Link to My Web Courses]
Agricultural Soil Physics and Mechanics [Link to My Web Courses]
General Soil Science [Link to My Web Courses]
Graduate (MSc and PhD) Courses:
Advanced Soil Physics [Link to My Web Courses]
A simple method for measuring unsaturated hydraulic conductivity of the soil is Outflow Method which was proposed by Gardner (1956). It makes use of cumulative outflow data vs. time of pressure plate apparatus or similar devices. I prepared a simple guide in PDF and an Excel File showing how to calculate the unsaturated hydraulic conductivity using this method.
Advanced Soil-Water and Plant Relations [Link to My Web Courses]
Plant Available Water (PAW), Least Limiting Water Range (LLWR) and Integral Water Capacity (IWC) are three approaches to characterize soil water availability to plants. While, PAW considers all of the soil water between FC and PWP totally and equally available, LLWR considers additional soil physical limitations such as aeration and mechanical impedance for calculation of available water. Gradual response of plants to soil physical restrictions is taken into account for IWC calculation. I and Hossein Asgarzadeh (my PhD student at BASU) prepared two files for calculations of PAW, LLWR and IWC in Excel:
We also developed a user-friendly software, called SAWCal (SAW Calculator), for calculating these quantities and other soil physical quality indices.
Soil mechanical impedance to plant root growth, as quantified by Penetration Resistance, is usually measured using a Cone Penetrometer e.g. Model CP20 (Rimik International Pty Ltd, Toowoomba, QLD 4350, Australia):
Cone Penetrometer Data Retrieval Program:
Gardner's model for root water uptake: Sample Calculations in an Excel File
Applications of Mathematical Models in Soil Physics
Error Functions [erf(x)] and Complementary Error Functions [erfc(x)] are needed for several analytical solutions of water and solute transport models and are used in soil hydraulic models like those of Kosugi (1994, 1996). An Excel File is available for calculation of erf(x) and erfc(x).
Boltzmann Substitution/Transformation is a technique to transform a partial differential equation into an ordinary differential equation. Example of applying this technique for analytical solution of Richards’ equation for horizontal infiltration into a soil column is given in an Excel File.
An interesting point on the soil water retention curve is “inflection point” at which curvature of the curve is zero or is changing from concave to convex. Dexter (2004a,b,c) proposed a soil physical quality theory (i.e., S-theory) and an index, S, which is the slope of water retention curve at its inflection point when the data is drawn as gravimetric water content vs. natural logarithm of matric suction (hPa). In an Excel File, I analyzed correspondences between different inflection points of soil water retention curve when using different versions of van Genuchten (1980) model. The relations between the inflection points and the model parameters are also included.
Solver is simple and very good Non-linear Optimizer in Excel [PDF]. This optimizer is ideal for many non-linear fittings in this course:
An interesting soil water retention model was developed by Kosugi (1994) by applying lognormal distribution law to the pore size distribution function. It was also included in RETC Program with a bit different formulation:
I use Excel Solver to fit 5-parameter and 4-parameter versions of the model to measured soil water retention data [Excel File]. The 4-parameter model fitting is also compared with RETC formulation.
Arya and Paris (1981) proposed a physic-empirical model for soil water retention curve which was the foundation of many physical and property-transfer models. A PDF File in Persian is prepared by me and Habib Hassanipour (my former MSc. student in BASU) to guide how to use this model and how to calculate best-fit scaling parameter for soil water retention modeling and prediction.
Pedotransfer Functions (PTFs) are prediction methods to predict “what we need” from “what we have”. The inputs are generally easily-available soil properties like texture, organic matter and bulk density and the outputs are hardly-available soil properties like soil hydraulic properties. I prepared a PDF File in Persian about PTFs and their types for prediction of Soil Hydraulic Properties.
Many models for water infiltration into the soil are found in the literature. I use Excel Solver to fit Kostiakov, Kostiakov-Lewis, Horton, Philip, Knight and Green-Ampt models to measured ponded/saturated infiltration [Excel File].
Disk/Tension Infiltrometer is a useful device to measure unsaturated infiltration of water into the soil. The data could be used to predict unsaturated hydraulic properties and parameters. Two well-known methods for analyzing the tension infiltrometer data are analytical Wooding’s (1968) analysis and numerical analysis (by DISC Software). I prepared an Excel File showing Wooding’s analysis. I also imported the analysis with DISC Software into this file.
Soil Mechanics [Link to My Web Courses]
How to calculate Effective Stress in Unsaturated Soils: [PDF]
How to calculate Tensile Strength of Soil Cores in Indirect Brazilian Test and modeling with a van Genuchten-type function: [Excel File]
Advanced Concepts in Soil Physics [Link to My Web Courses]
Plant Available Water (PAW), Least Limiting Water Range (LLWR) and Integral Water Capacity (IWC):
Research Methods [Link to My Web Courses]