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1. Varied depth of samplings. For example normally a 24 inch depth soil sample will analyze substantially less for phosphate than a 12 inch sample depth.
2. Combining unlike soil areas into one complete sample.
3. Combining like soil areas with different past liming, fertilizer, or cropping histories into one composite sample.
4. Combining an insufficient number of sub samples into composite from extremely varied or land-leveled fields.
5. Attempting to use single composite sample for too large an acreage.
6. Varying amounts of organic matter or undecomposed organic matter in sample.
7. Soft rocks in sample
8. Fertilizer or liming materials improperly applied or not thoroughly mixed in sol.
a-Material still on top of soil
b-Coarse materials not dissolved or not extract soluble.
c-Banded fertilizer applications not constituing a proper proportion of sample.
9. Sheet erosion (wend or water) of material applied.
10. Leaching of certain elements due to materials used, rates of application, or excessive water.
11. Drought-too dry for fertilizers to dissolve and become part of soils system.
12. Necessary soil microbes not present for proper release or conversion of fertilizers to available forms.
13. Forced drying of soil sample at too high of temperatures.
14. Soils that have been sampled with contaminated equipment, or dried, or processed in contaminated containers. Sample equipment hauled in a pickup with fertilizer or stored in a warehouse next to fertilizer has been a source of false high soil test results.
15. Improper packaging of samples, allowing contaminants to become part of sample.
16. Mixing sample identity, either field numbers or soil depths of profile samples.
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