Developing Soil Tests
A single numerical value reported by a soil test has no meaning unless the information gathered can answer the following three questions:
1) Will a specific crop attain maximum growth and/or yield at that soil test level?
2) Will crop growth or yield be greater when the nutrient is added to the soil?
3) Can the amount of nutrient needed for the crop to attain better growth or yield be predicted?
A vast amount of laboratory, greenhouse, and field research is necessary to develop a useful soil test. Chemical combinations called extractants remove nutrients from the soil. The nutrient in the extractant is then analyzed. The general principles behind extractant development are explained in the next section.