PO 19. Recognize how the following affect soil test interpretation

There is inherent environmental risk when applying nutrients.  Runoff from fields can contaminate water supply and pollute the nearby areas.  Soil test recommendations may consider this risk, as well as plant response, when developing fertilizer rates.  If the risk is high, the recommended rates may be lower than in other fields where there is low risk.

Studies have shown that no yield response to an applied nutrient will be observed if the soil levels of that nutrient are above a certain critical soil test level.  This is based on long-term calibration of soil tests, combined with local field yield response data. Thus, fertility recommendations are state-specific and sometimes even region-specific.  Keep in mind; soil testing for fertility management requires locally-applicable crop response studies that link soil test levels to probability of a crop response and actual nutrient needs.