Jarrod Miller, Extension Agronomist
University of Delaware recommends potassium (K) applications for low (0-70 ppm) and medium (71-140 ppm) soil test categories. However, soils in Delaware may have K that is not accounted for in a normal soil test, with minerals slowly release K over the growing season. Some of this was established by UD soil chemists in the 1980s, who observed high total K (not all plant available) in our soils, particularly in the sand fraction (https://www1.udel.edu/soilchem/Parker89SSSAJa.pdf). This means that some soils may need less K than is recommended by a regular soil test.
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