Guide to the Calibration of Soil Tests for Fertilizer Recommendations [antikvár]

- iii - Foreword The rationalization of fertilizer use in the developing world is quickly gaining importance. The general fertilizer recoiranendations which have been developed during the last two decades for large agricultural areas throughout the world were based on thousands of small experiments carried out under conditions of practical farming. This technique of small trials, which is described in an earlier FAO Soils Bulletin, led very quickly to fertilizer recommendations which were safe for the farmers as they resulted in high monetary returns. They did not, however, take into account the specific conditions of individual fields which would lead to even higher yield increases and benefits. Individual fertilizer recommendations for each field can only be based on chemical soil analyses since they are quick and efficient enough to follow for the testing of many fields for many farmers per season. The difficulty in putting this well-known principle into a practical and efficient system is the interpretation of soil test data in terms of fertilizer requirements which varies from region to region. This calibration of soil tests is done by the various soil testing laboratories in industrialized countries in very different ways, each working rather isolated from the others. Most of the specialists in the laboratories of developing countries, be it FAO or national specialists, who want to calibrate their soil test values for improving fertilizer recommendations on a field to field basis, have no or little access to the calibration methods used elsewhere, mainly because these methods are not usually published. Nor do they have time and resources to visit many laboratories and to develop from the obtained information their own calibration methodology. The purpose of this Bulletin is to serve as a guide for the mentioned specialists. It is the first attempt to compile and develop from the experience and information of various successful soil testing laboratories a suitable methodology for each step of the soil test calibration into a calibration system which can be applied under most varied soil and climatic conditions. The hope is expressed that all those specialists who use this guide wholly or partly may communicate back to the Soil Resources Development and Conservation Service of FAO their experiences, opinions and obtained results. These will contribute most fruitfully to the build-up of a stock of experience on problems and difficulties met under the various conditions, which may eventually lead to an improved second edition of this guide. Edouard Saouma Director Land and Water Development Division