Interpretation of soil tests: a review

Abstract

Soil tests tell how much nutrient is extractable, some of which may be present in a plant-available form, and/or the amount that may become available to the crop or pasture. This is a quantitative measure of nutrients. Interpretation depends on the skill of interpreters, and a major factor in interpretation is experience. Accurate interpretation is only possible when the sample collected from the field is representative of the site, and this can best be achieved using monitor plots rather than the traditional zig-zag method of sampling. One of the main deficiencies in experimental data used to interpret soil tests is the poor characterisation of experimental sites and of the climatic conditions during the experiment. Better characterisation would allow better interpretations to be made. With the development of equipment that is able to analyse multiple elements (e.g. ICP-AES), investigation of multiple extractants should be expanded in Australia. Of these, the Mehlich No. 3 and AB-DTPA extractants would seem the most appropriate. Because of the frequent relocation of agriculture advisers, experience is often lost; hence, there is a need for GIS/Expert systems to gather this experience. The development of such systems will allow new personnel to understand more rapidly the characteristics of soils, climate, and crops in an area. The final decision on fertiliser rates depends on the financial situation of the farmer. Soil testing and interpretation of these results is just 1 factor used to make the fertiliser decision.