Electrical Conductivity Spots Salty Soils
Electrical conductivity (EC) measures the amount of salt
in a field as well as the field's compositionthe amount of sand,
clay, and organic matter. Farmers want to know the composition of their
soil so that they can apply the correct number of seeds and chemicals
to each section of their land. A farm with varying soil composition
can be subdivided into sections according to EC data.
engineer Hamid Farahani and his fellow researchers at the Water Management
Laboratory in Fort Collins, Colorado, have shown that EC data can be
a practical tool in determining how effective changes in irrigation
water management practices have been in minimizing the buildup of salts
in the crop root zone. In cases where there is no buildup of salts,
any measured variability in EC would reflect changes in soil composition
across the field.
Farahani uses a pickup truck to pull a machine that measures
electrical conductivity of the soil. As the truck maneuvers over the
field, two EC readings are taken every second: one that measures the
top foot of the soil and another that measures the top three feet. A
140-acre field can be driven in 6 hours, giving about 14,000 data points.
A Global Positioning System (GPS) mounted on the truck
links to satellites and tells a computer exactly where each data point
is in the given field. This is similar to the devices found in some
cars that can locate them if stolen.
Farahani puts the information collected into a special
computer program to get an indication of the changes in salt loads across
the fields. Different colors show the amount of EC within the field.
With this machine, farmers can quickly get a map of their field's variability.
Using the EC map as a guide, farmers only need to collect a few soil
samples from each specific EC area to determine soil composition and
decide whether or not to modify management.
Without this machine, it would take days to collect enough
samples to make a similar map, and it would cost significantly more.
Farahani has gone back to survey farms 2 or 3 years later
to find only small changes in EC, which indicates good irrigation practices.
Drastic changes would have indicated problems in the overall management
of the irrigation water.By David Elstein, Agricultural
Research Service Information Staff.
"Electrical Conductivity Spots Salty Soils" was published in the December 2002 issue of Agricultural Research magazine.