New Method To
Measure Water and Chemical Movement in Soil
September 24, 2001
A new measuring method adaptable
for field use will increase the accuracy of mathematical models that estimate
potential groundwater contamination by agrochemicals,
Agricultural Research Service scientists
Many computer models are available for predicting the fate and transport of
agrochemicals applied to soil. However, before they can be accurately applied
to specific situations--like more precise modeling of water and chemical
movement through soils--the parameters required for input into the model must
be measured or estimated for the soil of interest.
One group of models that would be useful for estimating rapid movement of
water and chemicals through undisturbed, natural soil has been little used
outside the laboratory because of difficulty in measuring these necessary model
Now, ARS soil scientist Dan B. Jaynes at the National Soil Tilth Research Laboratory in
Ames, Iowa, working with researchers at Iowa
State University-Ames and Iwate
University, Iwate, Japan, have developed and validated a new method. It is
a quick and easy method for measuring water and chemical movement in soil.
They use time domain reflectometry (TDR) to characterize solute transport in
undisturbed, structured soils with distinctive flow properties. TDR works like
radar, measuring the time and distance of reflected electrical signals in metal
rods that are inserted into 8-inch-long by 5-inch-diameter columns of
undisturbed, structured soil.
In their study, the scientists tested a TDR method under controlled
laboratory experiments and found that the reflected signals were directly
related to important soil properties.
The TDR method is simple and minimally disruptive. It provides estimates of
field soil properties that enable scientists to predict how water and chemicals
will move through the soil.
Scientists using the new method will be able to obtain model parameter
estimates as reliable as the more traditional but time-consuming measurement
ARS is the U.S. Department of
Agricultures chief scientific research agency.