Relationships between the Mehlich-III soil test extraction procedure and standard soil test methods in North Dakota

One hundred surface soil samples were randomly selected from actual farmer samples submitted to the North Dakota State University Soil Testing Laboratory for comparing the usefulness of the Mehlich-III extractant with results from currently used methods for extracting, phosphorus (P), potassium (K), zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) from neutral to alkaline pH soils from the northern Great Plains. Soil pH's were distributed across a range from pH 7.0 to 8.3. The Mehlich-III extractant correlated well with P, K, and Zn values obtained by the Olsen, neutral normal ammonium acetate (1M NH4OAc, pH 7.0) or DTPA (diethylenetriamenepentaacetic acid) extraction procedures, respectively. The Mehlich-III extractant was somewhat correlated with Cu by the DTPA method but poorly correlated with DTPA-extractable Fe and Mn. The Mehlich-III extractant appears to be adequate for extraction of P, K, and Zn across concentration ranges normally found in most agricultural soils in North Dakota.