By Keith Bellingham, P.H. Soil Scientist /Certified Professional Hydrologist
kbellingham@stevenswater.com
Dr. Martinus Th. “Rien” van Genuchten has been awarded the Wolf Prize Laureate in Agriculture 2023 which is considered by many to be equivalent to a Nobel Prize. The award citation reads “for his groundbreaking work in understanding water flow and predicting contaminant transport in soils.” During a career spanning nearly a half century, Rien made significant contributions in soil hydrology and pioneered numerous ways to estimate and predict soil water movement. A quick Google search for van Genuchten will yield over 500,000 results as a tribute to all his achievements in hydrology and soil science.
Read the full article from Wolf Foundation https://wolffund.org.il/martinus-th-van-genuchten/
Dr. van Genuchten began his career with his education at the Wageningen Agricultural University in The Netherlands and then finished his PhD at New Mexico State University. From there Dr. van Genuchten had a 40-year tenure at the prestigious United States Salinity Lab in Riverside, California.
Soil water movement has significant environmental implications in agriculture, irrigation, and food security but is also a key ingredient for predicting regional droughts, groundwater and surface water availability, flood modeling and contaminant transport.
In 1980, Dr. van Genuchten published a groundbreaking paper since referenced tens of thousands of times, “A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils”, Soil Science Society of America Journal 1980, 44:892-898. Rien introduces what is now referred to as the van Genuchten Equation. This equation mathematically transforms the relationship between a soil’s matric potential to the volumetric water content.
The soil’s matric potential (SMP) is the amount of pressure required to pull water out of soil. A plot of the volumetric soil moisture on the Y axis and matric potential on the X axis is called a soil water retention curve as shown above. Dr. van Genuchten determined a mathematical formula using just two soil parameters and two fitting parameters. This makes it possible to easily convert SMP – an indication of crop stress – into a volumetric water content which provides greater insight into the amount of irrigation water needed.
The van Genuchten equation shown above, converts a soil’s hydraulic head in meters, h, a parameter related to matric potential, into volumetric soil moisture symbolized by the Greek letter Theta, θ. The parameter θs is the soil moisture at saturation, θr is the residual soil moisture and α, n and m are empirical fitting parameters unique to a particular soil. The m term is calculated from n. The residual soil moisture is observed in drier conditions where the microscopic channels of water in the soil’s pore spaces become disconnected and substantial changes in head occur with minor changes in soil moisture.
Since the 1980s, the US Department of Agriculture and many other natural resources institutions began testing soils of many types and textures and published the van Genuchten parameters, α, n, θs, and θr in manuals and documents available to the public. Below is an example of soil survey data showing the van Genuchten parameters for a topsoil and a subsoil. Many counties and areas in the United States publish regional soil surveys that include the van Genuchten parameters.
Dr. Martinus Th. van Genuchten is one of the few soil scientists to win the Wolf Prize Laureate. Stevens and SoilMoisture are excited to join in congratulating Dr. van Genuchten for this once in a lifetime honor.
