The DTPA (diethylenetriaminepentaacetic acid) micronutrient extraction method is a non-equilibrium extraction for estimating the potential soil availability of Zn, Cu, Mn, and Fe. It has been used for cadmium, nickel and lead in soils. The method has shown to be well correlated to crop response to fertilizer for zinc and copper. The amount of micronutrients and trace metals extracted are affected by solution pH, temperature, soil extraction ratio, shaking time, extraction time, and extractant concentration. Extracts are analyzed by ICP-OES. The method has a detection limit of approximately 0.1 mg/kg for Zn, Cu, Mn, and Fe and is generally reproducible within 10% for Cu and Zn and 15% for Fe and Mn. The method is not well characterized for other elements.
Lindsay, W. L. and Norvell, W. A. 1978. Development of a DTPA soil test for zinc, iron, manganese, and copper. Soil Sci. Soc. Amer. J. 42:421-428.