The Use of Isotopes to Obtain Field, Greenhouse and Laboratory Data to Evaluate P Effects

Specific techniques that have proven successful in evaluating P effects are described and discussed in relation to their application to( field research investigations. 'A'-values using seed placement of the tagged-P carrier, while primarily a technique used to measure available soil-P or the relative availability of different P carriers, has proven a reliable means of estimating the effects of many secondary factors on soil-P availability, i.e. soil moisture stress, biological fixation or release of soil-P, volume of root exploitation, or soil temperature, etc. The relative significance of criteria such as 'A'-value obtained from field experiments growth chamber 'A'-values, Scott A. Russell's Pe-values, McConachy's IDF-values, phosphorus fractionnation (Al, Fe, Ca bound-P), and NaHCO₃ extractable-P is discussed in relation to data obtained on four sub-group profiles of a chernozemic soil developed on medium textured lacustrine materials. The P-32 injection technique has proven a simple and rapid means of measuring the effects of fertility treatments, soil type and moisture stress on the rooting habits of wheat. A modified plot design for field experiment was discussed. (author)