BASIC EDTA AS AN EXTRACTANT FOR SOIL ORGANIC PHOSPHORUS

Soil organic P is an important source of plant-available P in the Grea t Plains. It is, therefore, important in conservation tillage agricult ure, that we know the size and the potential availability far crop use of this large P pool, which could exceed one-half of the total P. We propose a one-step procedure with hot basic EDTA (ethylene diaminetetr aacetic acid) for total soil organic P that requires minimum manipulat ion and analytical prowess. Soil samples (0.5 g) were incubated for 2 h at 85 degrees C with 25 mL of 0.25 M NaOH + 0.05 M Na(2)EDTA, after which time the organic P in the extracts was determined by persulfate oxidation. Results from the evaluation of nine soils from various part s of the USA and one Canadian soil showed significant correlations wit h an existing wet sequential extraction and a dry high-temperature ign ition method for total organic P determinations. With the high-organic -matter Canadian soil, the EDTA method extracted 32% more organic P th an the wet extraction method, and essentially the same as the dry igni tion method. The new method appears to be especially useful for soils where organic acids and chelation mechanisms with P may be mere domina nt than ester-type formations.