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Field Calibration for Corn of the Mehlich‐3 Soil Phosphorus Test with Colorimetric and Inductively Coupled Plasma Emission Spectroscopy Determination Methods
Author(s) -
Mallarino Antonio P.
Publication year - 2003
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2003.1928
Subject(s) - inductively coupled plasma , chemistry , analytical chemistry (journal) , soil test , phosphorus , inductively coupled plasma atomic emission spectroscopy , soil water , coefficient of determination , zoology , environmental chemistry , mathematics , soil science , environmental science , plasma , biology , statistics , physics , organic chemistry , quantum mechanics
Use of the Mehlich‐3 soil extractant with an inductively coupled plasma emission spectroscopy (ICP) determination method (M3‐ICP) is displacing the original colorimetry‐based test (M3‐COL). Current interpretations do not distinguish between these two versions, although the M3‐ICP test often measures more P. This study correlated these tests and the Bray‐P 1 (BP) test with corn ( Zea mays L.) yield response at 59 Iowa locations (78 site‐yr). The mean P measured by the M3‐ICP, M3‐COL, and BP tests was 31, 19, and 17 mg P kg −1 , respectively. The M3‐ICP/M3‐COL ratio decreased exponentially with increasing soil P ( P ≤ 0.01) but their difference was not correlated with soil P. Relative or absolute differences tended to decrease linearly ( P ≤ 0.01) with increasing soil pH or organic C, but the strength of the relationship was poor ( R 2 = 0.14–0.32). The BP test measured significantly less P in a CaCO 3 –affected soil (pH 8.1). The R 2 of the relationship between M3‐ICP and M3‐COL was 0.84, and was 0.89 between the M3‐COL and BP (0.97 excluding the site with pH 8.1). Critical concentrations defined by Cate‐Nelson and linear‐plateau models for the M3‐ICP, M3‐COL, and BP tests were 20 to 32, 16 to 21, and 13 to 20 mg kg −1 , respectively. The M3‐COL and M3‐ICP are equally effective for Iowa soils but interpretations differ. The M3‐ICP test should be considered a different test and its interpretations should be based on field calibrations rather than conversions based on M3‐COL data. A range of 25 to 35 mg kg −1 for the M3‐ICP test would correspond to the optimum class (16–20 mg kg −1 ) used in Iowa for the M3‐COL and BP tests.