Convenient estimation of soil organic‐N using the Udy dye system

A method was developed for conveniently estimating organic‐N in soils using Udy dye, which is bound on the positive sites of the soil organic matter complex. The quantity bound is associated with the quantity of organic‐N. These amounts can be determined by initially adding an excess of dye and, after equilibrium, colorimetrically measuring the amount remaining in solution. A soil pretreatment wash with water and oxalic acid is used to remove soil solution coloration, buffer the soil pH, and precipitate soluble soil calcium. High amounts of soil free iron oxides or carbonates interfered with the test.