The Soil Testing and Fertility Program
The cornerstone of any well designed fertility program is a sound soil testing program. Soil testing is essential for making wise fertility program decisions. However, it is important to remember that a single soil sample or test from a field has only limited value since soil test values may vary from year-to-year. The real value is the development of a soil test history so that trends can be evaluated and acted upon. Unfortunately, large acreages of wheat have little, if any, soil test history, and providing a fertility history is really what soil testing does best.
A common complaint about soil testing is that different recommendations often result if the same sample is sent to different laboratories, both University and commercial. There are several things to keep in mind relative to these concerns. First, the final product of soil testing is not a specific prescription for the amount of fertilizer to apply to a specific field. The product of soil testing is an additional piece of important information to use when developing a farmer/field specific fertility recommendation. Second, fertilizer recommendations must include more than just a suggested application rate, application method and timing are equally important. Third, differences in rate recommendations are generally the result of a difference in the interpretation of analytical results and not a difference in laboratory analytical values. And finally, soil testing is not the same thing as fertilizer recommendations; these terms should not be used interchangeably.
The following steps are involved in developing a fertility program for a specific farmer/field utilizing soil testing:
1. Collecting a good representative sample (representative of field or portion of field).
2. Proper care of the sample after collection (contamination, microbial processes, etc.).
3. Chemical analysis at laboratory (appropriate tests that have regional meaning).
4. Interpretation of analytical results relative to the historical research base.
5. Integrating interpretations to fit farmer/field specific goals and conditions.