New Method To Measure Water and Chemical Movement in Soil

By Jennifer Arnold
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 report.

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 parameters.

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 methods.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.