EXPLORING CATION EXCHANGE CAPACITY THROUGH THE USE OF
THE SOIL SURVEY
Scott Werts
Winthrop University
Design of Activity Activity designed as a homework assignment Work assigned after lecture material and
reading on cation exchange processes in soils.
Students are not to work in groups, and each is responsible for choosing their own locations to investigate
Students in this course already have a background in using the NRCS Online Soil Survey
Assignment Basics
Students are to compare the cation exchange capacity of a particular set of soils with the aspects of that soil that influence the CEC. (pH, organic material and clay)
Students may chose any location they wishMost chose their address or an address of
their relatives.
Assignment Basics
Students look at this data at two separate depthsEach set of data is taken from 0-10 cm and
10-20 cm.This gives the students an idea of variation
within the area laterally with different soil types and vertically within the same soil type.
Familiarity with the Online Soil Survey Online Soil Survey
A clearing house of very basic data regarding soils.
Assessment
Students are to turn in:The map of the Area of Interest they created
(AOI)A Table displaying
○ Soil types○ CEC○ Percent Clay○ Percent Carbon○ pH
Explanation of trends….
Assessment
TrendsWhat should be:
○ As CEC goes uppH goes downOrganic Content goes upClay goes up
Sometimes there is variation○ pH will go down as organic content goes up,
for example
Variation from the norm:
Have the students assess the magnitude of the differences.For example – a 10% increase in organic
matter may be a stronger driver for an increase in CEC than a 0.2 drop in pH.
Variation from the norm:
Not fool-proofAt least once, there was a trend even I, the
professor, could not explain.Reinforce that the soil survey isn’t perfect
and should represent a generalized trendI had the student write what should influence
the CEC and state that the data bucked the traditional trend we discussed in class
Questions?
Happy students!