Testing Soil for Micronutrients

Soil testing for micronutrients is increasing throughout the United States. Many commercial fertilizer companies include these tests as a regular part of their service. For any valid soil test there are four main features that need careful consideration. First, the sample must represent the area sampled and must have been treated in such a manner as to avoid contamination or drastic change in the status of the nutrient under consideration. Second, the conditions for extracting the nutrient must be such that the amount extracted is related to the available nutrient supply. Third, the nutrient in the extract must be determined quantitatively and fourth, interpretation of the results must be based on reliable calibration data. In addition to these criteria, before a soil test is accepted and used widely, it must be reduced to a routine operation at moderate cost. Detailed discussions of the chemistry of the micronutrients in the soil are given by Mitchell (19) and Hodgson (14). Comprehensive discussions dealing with various aspects of soil testing are available in a recent monograph (11) which includes a discussion by Viets (34) on soil testing for the micronutrient cations. Many of the wet chemistry procedures (3) for determining the micronutrients are time consuming and require highly trained personnel for accurate analysis. The advent of atomic absorption spectrophotometry, however, has eliminated many of the analytical problems and offers straightforward procedures that are free from interferences and may be used routinely