Basic Edta as an Extractant for Soil Organic Phosphorus

Abstract

Soil organic P is an important source of plant‐available P in the Great Plains. It is, therefore, important in conservation tillage agriculture, that we know the size and the potential availability for 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 diaminetetraacetic acid) for total soil organic P that requires minimum manipulation and analytical prowess. Soil samples (0.5 g) were incubated for 2 h at 85 °C with 25 mL of 0.25 M NaOH + 0.05 M Na₂EDTA, after which time the organic P in the extracts was determined by persulfate oxidation. Results from the evaluation of nine soils from various parts of the USA and one Canadian soil showed significant correlations with an existing wet sequential extraction and a dry high‐temperature ignition method for total organic P determinations. With the high‐organic‐matter Canadian soil, the EDTA method extracted 32% more organic P than the wet extraction method, and essentially the same as the dry ignition method. The new method appears to be especially useful for soils where organic acids and chelation mechanisms with P may be more dominant than ester‐type formations.