SL410 Fertilizer Recommendation Philosophies 1 George Hochmuth, Rao Mylavarapu, and Ed Hanlon 2 1. This document is SL410, one of a series of the Soil and Water Science Department, UF/IFAS Extension. Original publication date October 2014. Visit the EDIS website at http://edis.ifas.uf.edu. 2. George Hochmuth, professor, Soil and Water Science Department; Rao Mylavarapu, professor, Soil and Water Science Department; and Ed Hanlon, professor emeritus, Soil and Water Science Department; UF/IFAS Extension, Gainesville, FL 32611. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or afliations. For more information on obtaining other UF/IFAS Extension publications, contact your county’s UF/IFAS Extension ofce. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension. Soil testing is an important frst step to fertilizer (nutrient) management on the farm, and using a calibrated soil test extractant is critical to the success of soil testing and fertil- ity recommendation programs. We explained soil testing and its usefulness in EDIS document SS621, Soil Testing for Plant-Available Nutrients—What Is It and Why Do We Use It? (Hochmuth, Mylavarapu, and Hanlon 2014). Once the soil test index is interpreted, a fertilizer recommendation is provided to the farmer that includes the amount of fertilizer to use for the crop and guidelines on fertilizer management. In addition, soil test reports provide information about soil pH and lime requirements. Tis discussion focuses on phosphorus, potassium, magnesium, and calcium. Even though various soil testing labs may interpret the soil test index similarly, laboratory reports may vary in the fertilizer recommendation. Farmers notice this variation in recom- mendations when they send the same soil sample to various labs and receive diferent fertilizer recommendations. What are the reasons for this apparent discrepancy in fertilizer recommendations? Farmers receive varying fertilizer recommendations depending on which lab they consult because labs (1) employ diferent chemical methods and procedures to analyze the samples and (2) subscribe to diferent fertilizer recommendation philosophies. (As we have discussed in previous publications of this series, the diferent chemical methods for soil tests are specifc to the nature of the soils and to the successful feld calibration of those methods.) Tis publication explains the main soil-test philosophies, their basis, and their applications, and explains why one of the three—the Sufciency Level of Available Nutrient philosophy (SLAN), also called the Crop Nutrient Requirement (CNR) concept—is most likely to be the best to govern fertilizer recommendations in Florida today. Figure 1. Manually spreading fertilizer on plots for a fertilizer rate and source study with tomato. Credits: George Hochmuth, UF/IFAS Archival copy: for current recommendations see http://edis.ifas.ufl.edu or your local extension office.