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It is possible to analyze soil samples for any of the 13 essential elements which plants obtain from the soil. This does not mean that the results obtained can be used to predict adequacy or deficiency for plant growth.
The value obtained from any chemical procedure used to determine each element must be shown to be related to (1) crop response from application of that element (correlation) and (2) the soil test level at which response occurs (calibration). Crop response is usually measured as yield, but may also be a quality factor. Field plot and greenhouse research are used to study these relationships on a range of Nebraska soils, so that soil tests can be used effectively to determine crop needs for fertilizer.