lurry and Moist Methods
A Wet K test focuses more on purely exchangeable potassium. There are two
primary Wet K methods, both developed at Iowa State University. The “Slurry”
method, adopted in the 1960s, and the “Moist” method, developed in 2006.
The two methods are highly correlated and produce comparable end results.
See Graph 1.
Accuracy
The goal of a soil test is to take a representative sample from a highly
complex system and use the results to make the best possible management
decision. Neither testing method is “correct” in an absolute sense, but both
are valuable tools. Each method presents its own useful information. When
making potassium assessments, both data sets offer useful agronomic
information. Looking at only wet K
test results ignores the portion of the
potassium that is slowly available and
that which can be released through
the normal biological and chemical
processes. Utilizing only a dry K test
ignores the fact that potassium moves
between the two phases of available
K and slowly available K. This process
is what causes potassium soil test
levels to vary from one year to the
next. Together, wet and dry test data
sets act as a double check of soil
potassium fertility levels.
If both the wet K and dry K test results are low, then the need for additional
potassium fertilizer is the greatest.
Interpreting Wet K
What is a high, medium or low soil test? See the reference table, developed
at Iowa State, located below. It is important to note that the wet K test has its
own interpretation table. The Iowa State current “standard” chart cannot be
used for evaluating wet K results.
In Conclusion
AgSource offers two potassium testing
methods: standard (dry) and moist (wet).
For the most complete understanding of a
field’s potassium needs, compare wet K and standard K test results.
When reviewing test reports, be sure to reference the correct wet K and
standard K interpretation tables. Contact AgSource today to learn more
about how these tools can help improve your understanding of soil
potassium levels. More information can be found at www.agsource.com.
©2012 CRI F-03510-12
Potassium Analysis WET SOIL METHOD
Graph 1 – Slurry and Moist Method Correlations
Wet K (ppm) Standard K (ppm)
Very Low 35 90
Low 68 130
Medium 100 170
High 150 200
Very High 150+ 200+
Wet
K
Standard
K
Linco