Abstract:
The purpose of this chapter is to describe how bioavailable soil K is
assessed or predicted by soil tests. Soil testing commonly refers to the collection of a
sample of soil representative of a field or agronomic management unit and, by way
of extraction using chemical reagents, determination of the quantity of a nutrient that
can be related to plant uptake or yield. Normally only a small fraction of the total
quantity of the nutrient present in the soil is extracted during the procedure, but if
that amount can be correlated with actual crop uptake or overall crop productivity,
then the soil test is deemed to have useful predictive power.
Soil tests are routinely used to guide applications of fertilizer to soil so that crop
demand for nutrients can be met effectively and economically. Here, we summarize
the procedures involved in collecting a representative soil sample for K analysis,
outline how that sample should be prepared for laboratory analysis, highlight the
principles and mode of action of routine soil tests, and explore some common issues
that may confound the correlation between a soil K test result and plant K acquisition
or crop yield. Soil testing methods are discussed in the context of their relationship to
the different forms of soil K and the in-soil chemical processes that may change these
forms into K that can be taken up by roots.
