Using Soil Tests to Make Fertilizer Recommendations: A Historical Perspective.

Soil tests have been used to make fertilizer recommendations for nearly a century.  During this period the soil testing and fertilization process has changed substantially, as has the fertilizers available, methods of fertilizers application used and some of our expectations from fertilizer use.  However one thing that has remained constant throughout that time period has been the overall objective of agronomists to provide fertilizer recommendations which give the highest economic returns to farmers fertilizer investment.  Some of the concepts covered in this paper will be the development of soil test correlation and calibration concepts, the nutrient sufficiency and build and maintain recommendation systems and some thoughts on why regional differences in the fertilizer recommendation  process occurred.