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!