A soil test measures the relative soil fertility levels. It is a basic tool in planning an economically and environmentally sound fertility program. Plant analysis, on the other hand diagnoses or confirms diagnoses of a visible symptom. Combined with the soil test information, plant analysis allows fertilizer management to be fitted more closely to a crop's needs.
More information can be found on the Extension website at http://soilplantlab.missouri.edu/soil/.
Revised Soil Test Flyer 2011 (PDF)