Determining whether or not a swath of soil will lend itself to agricultural use usually requires extensive testing, which may disrupt the soil and can be time-consuming. Now a report published in the October 28 issue of Physical Review Letters outlines a quick, noninvasive way of estimating soil's suitability for planting. Researchers have used microwave radar to determine the physical and mechanical properties of a section of earth without disturbing it.

Klaudia Oleschko of the National Autonomous University of Mexico and her colleagues determined that although soil structure is extremely heterogeneous, on the scale of one centimeter to one meter it is also a fractal. That is, patterns that can be described with relatively simple equations are repeated over varying size scales. The scientists exploited this property to identify the volume of empty space--a good indicator of density and water content--within a sample of dirt. Microwaves reflected by a soil sample, the team found, had the same fractal dimensions as the sample itself. When the researchers used microwaves to scan a cube of earth with six very different layers (see image), the results obtained from the radar technique agreed well with direct measurements taken from each of the sections. The authors conclude that ground-penetrating radar is "a prominent tool for nondestructive soil studies."