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shrinking world inside agriculture
21st-century soil science
In 1959, when Cal Tech physicist Richard
Feynman advised scientists to examine the "small world that
is below," he literally didn't mean the earth below them. But Cliff
Johnston, Purdue professor of agronomy, has found a world of
opportunity in the soil by examining the nanostructure of clay particles.
At the bulk scale, clays are inert and not particularly
useful. But, like other materials, clays at the nanoscale don't
behave in the linear, simple fashion that they do on a larger scale.
And that variable behavior makes them very useful in a variety of
applications. But it also means that how we think about clays in
the environment may be wrong.
Inert at the bulk scale, individual clay particles
have an electrical charge that varies along the surface of the particle.
"The distance between charge sites can vary between one and three
nanometers, and that is important because organic molecules, such
as pesticides, have similar dimensions," Johnston says. "Now we
can develop a molecular picture of what's happening in these types
of structures."
This finding means that chemicals that were thought
to rush by clay as they passed through the soil may in fact be held
up for a time. Or, the chemicals may even be chemically degraded
by the surface of the clay.
"For a large group of pesticides, the conventional
wisdom was that they had little to do with clay surfaces. For the
most part, these would interact with organic material in the soil,"
Johnston says. "But now that we're developing more sophisticated
ways to look at these systems, we're finding that some pesticides
have greater affinity for clay surfaces than for organic materials
in the soil. This allows us to develop better models of how these
compounds are going to behave in the environment."
The manipulation and understanding of clays at the
nanoscale is important for many areas. Many new plastics contain
clays, as do vaccines used to protect human and animal health.
These vaccines are made up of two parts, a biological
protein attached to an inorganic particle, similar to a clay particle,
which delivers the vaccine within the body. Johnston, along with
Stanley Hem, Purdue professor of physical pharmacy, is working to better
understand the structure of these particles in vaccines so that
the next generation of vaccines will be more effective.
A shrinking world inside
agriculture
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