Interlaboratory Validation of the Mehlich 3 Method as a Universal Extractant for Plant Nutrients

Abstract

The Mehlich 3 (M3) method is widely used to extract plant-available phosphorus from soil over a wide range of pH values. The method is also used by many laboratories to determine multiple plant-available nutrients simultaneously. However, except for P, this method has not been statistically validated within and among laboratories. The objective of this study was to determine the repeatability (within-laboratory performance) and reproducibility (among-laboratories performance) of the M3 method for several different nutrients by using a wide variety of soils. An in-house homogeneity test was conducted for 11 soils. Three replicates of each of the 11 soils were sent to 23 domestic and international laboratories for analyses primarily for K, Ca, Mg, Zn, Mn, Fe, and Cu. Samples were scooped, weighed, or both scooped and weighed for extraction. The various nutrients in the extracts were quantified by the participating laboratories by using inductively coupled plasmaatomic emission spectrometry. Ranges (in parentheses) of the repeatability relative standard deviation (RSDr) values for the scooped samples were K (3.886.14), Ca (2.1910.6), Mg (2.275.73), Zn (4.1142.7), Mn (3.158.53), Fe (2.327.74), and Cu (3.6511.2). For the weighed samples, the ranges (in parentheses) of the RSDr values were K (1.654.65), Ca (1.4316.9), Mg (1.379.83), Zn (2.6033.0), Mn (1.614.90), Fe (1.564.47), and Cu (2.9517.9). Ranges (in parentheses) of the reproducibility relative standard deviation (RSDR) values for the scooped samples were K (7.4420.0), Ca (7.1033.5), Mg (7.6326.4), Zn (11.648.7), Mn (10.519.7), Fe (12.422.0), and Cu (8.8645.3). Ranges (in parentheses) of the RSDR values for the weighed samples were K (3.4712.7), Ca (7.6134.6), Mg (7.5329.0), Zn (10.649.2), Mn (6.5420.7), Fe (11.021.5), and Cu (9.7343.0). The Horwitz ratios (HorRat) were also used to evaluate the repeatability, HorRatr, and the reproducibility, HorRatR. Overall, the M3 method appears to be both repeatable and reproducible across the two categories for K, Mg, Zn, Mn, and Cu, and the vast majority of the HorRat values for both repeatability and reproducibility were within the acceptable range. However, a large number of soils in both the weighed and scooped categories displayed unacceptable HorRat values for the reproducibility of Ca and Fe, indicating that the M3 is not suitable for the extraction and quantitation of Ca and Fe in soils. The results of this study indicate that the M3 method for the determination of K, Mg, Zn, Mn, and Cu in soils is both accurate and precise when standardized procedures are used. The method has been proven to be suitable for use as a reference method for testing soil materials for extractable P, K, Mg, Zn, Mn, and Cu. Further study may be needed to confirm the suitability of the M3 method for Ca and Fe.

Water spreading weirs altering flood, nutrient distribution and crop productivity in upstream–downstream settings in dry lowlands of Afar, Ethiopia

“…The samples were analyzed for various chemical and physical properties in three replications in HORTICUP laboratory at Debrezeit. The Bouyoucos Hydrometer method (Bouyoucos, 1962) was used for texture analysis, the Walkley and Black (1934) method for organic carbon; the Kjeldahl method (Kirk, 1950) for total nitrogen; the steam distillation method (Kister, 1992) for NO 3 -N and NH 4 -N and the Mehlich-3 method (Schroder et al, 2009) for other elemental determinations ( Table 3). The parameters include % clay, % silt, % sand, pH, EC, Ca, Mg, available P and exchangeable K, S, Cu, Zn, B, TN, OC, OM, NO 3 -N and NH 4 -N. The data were used to characterize and compare the spatial difference in Crop data Short maturing maize crop was planted following the occurrence of the second flood (mid-April for Belg season and mid-June for Meher season).…”

Use of copper in pine nurseries

“…"Available" copper can be estimated using various extraction methods: Mehlich 1, Mehlich 3, ammonium acetate (AA) and others (Davey 2002). The Mehlich 3 test is considered to be a "universal" soil extractant (Schroder et al 2009). Extractions of identical soil samples might produce values of 2.9 (Mehlich 3), 2.1 (diethylenetriaminepentaacetic acid) and 1.5 (Mehlich 1) μg-Cu g -1 (Gartley et al 2002;Mylavarapu et al 2002;Wang et al 2014).…”

“…Even when using the same extraction procedure, different laboratories will report different copper values for the same soil sample (White et al 1980;Schroder et al 2009;Santoro et al 2017). As a result, one laboratory indicated the copper level in one sample was very high while two other laboratories indicated the level was low (Table 2).…”

Metal accumulation by the ultramafic flora of Kosovo

“…After drying, they were ground and sieved at 2-mm mesh size. Soil samples were analyzed for basic physical (texture) and chemical features in the following parameters: total concentrations of Zn, Cd, Co, Cu, Ni, Pb, Mn, Cr, Fe, Ca, Mg, Na pH, soil conductivity and cation exchange capacity (CEC) (Ni, Ca and Mg using Mehlich-3 method) (Schroder et al 2010).…”

“…Exchangeable Ni, Ca and Mg (considered as the very labile and bioavailable fraction) in the different soil samples were determined by the Mehlich-3 method (Schroder et al 2010).…”