Mehlich 3 Evaluation Robert O. Miller ALP Technical Director Colorado State University Fort Collins, CO SERA-6 Meeting, Raleigh, NC, June 21, 2011 Miller, 2011

Observations M3 Phosphorus observations across proficiency programs have shown consistent differences between ICP and SPEC P analysis methods on specific soils. Although a majority of soil testing labs utilize ICP for M3 P analysis, many use nutrient calibration models based on SPEC analysis. M3 SPEC – ICP differences have been report to be insignificant and a nonissue, however differences remain relevant.

M-3 Comparison Miller, 2011 Proficiency program M-3 P comparisons SPEC vs ICP Correlative soils properties with M-3 P Differences M-3 Solution Instrument Calibration, P and K

M3 P Spec and ICP Comparisons Miller, 2011 M3 P methods comparison of proficiency data (NAPT) have suggested method bias difference, however the database lacks intra- lab measurement error. M3 soil data from the ALP Program, with intra-lab error, provides conclusive evidence P analysis method differences, which are soil dependent. Of 70 ALP soils, 32 indicate a statistical significant difference between SPEC and ICP P values. SRS-0702 SRS-0702 * SRS-0703 * SRS-0705 SRS-0705 * SRS-0715 * SRS-0804 * SRS-0901 SRS-0901 * SRS-0906 * Soil ID M3-P Spec M3-P ICP MeanStdevMeanStdev M3 P methods significant different at the 0.05 level, three replications multiple labs

Miller, 2011 Mehlich 3 P Spec vs ICP 1:1 line 70 Soils, Collected from Thirty States - ALP ALP Data base y = 1.15x y = 1.15x R 2 = 0.957

Mehlich 3 P Spec vs ICP Relative % Difference M3-P Range (ppm) > 60 % Diff Miller, Soils, Collected from Thirty States - ALP ALP Data base

Mehlich 3 P Spec vs ICP Parse soil pH < 7.3 (0.01 M CaCl 2 ), N = 50 1:1 line Miller, 2011 ALP Data base

Mehlich 3 P Spec vs ICP Relative % Difference Miller, 2011 Reduced Data Set, pH < 7.3 (0.01 M CaCl 2 ) pH < Soils, pH < 7.3 ALP Data base

Mehlich 3 P Spec vs ICP Delta Correlation Property 1 Correlation pH sp pH (1:1) M3-K SOM-WB Sand % Silt % Clay % Miller, Correlations, soil pH < 7.3, phosphorus methods removed. 28 soils ALP Data base Reduced Data Set, pH < 7.3 (0.01 M CaCl 2 )

Eliason, Lamb and Rehm, Soils - MN

M3 P Spec and ICP Comparisons Miller, 2011 Differences in M-3 between SPEC and ICP can be described as Non-Reactive Phosphorous(NRP). Differences in M-3 between SPEC and ICP can be described as Non-Reactive Phosphorous (NRP). Large NRP differences primarily associated with M3 P levels less than 40 ppm. High NRP is identified with soils with low pH, high sand content and low silt contents. Maybe associated with aluminum. Soils with high NRP were collected from Oklahoma, Arkansas, Iowa, eastern Nebraska and eastern Illinois. No-Till soils greater difference.

Mehlich 3 Standard Solution Evaluation ID 1 P (ppm) K (ppm) Bottle # Bottle # Bottle # Bottle # Bottle #5 00 Bottle #6 ?? Bottle #7 ?? An evaluation of seven M3 solutions was conducted in 2010 of 24 labs. Seven bottles were prepared, #1- #5 from reagent solution standards, #6 - #7 of soil extracts. Reagent standard solutions balanced ionic strength. Laboratories analyzed for P, K, Ca, Mg, Na and Zn each in triplicate in ALP Cycle 12. Miller, Submitted ALP Program Cycle 12. Bottles #6 and #7 soil extracts of ALP of SRS-0802 and SRS-0715.

Mehlich 3 P Calibration Evaluation An evaluation of M3 3 solutions was conducted in ALP Cycle 12, 12 labs participating. ICP Labs 12, sorted by low standard Miller, 2011 ID 1 P (ppm) Bottle #1 8.2 Bottle # Bottle # Bottle # Bottle #5 0 Lab #12 has P precision issue across standards

Mehlich 3 K Calibration Evaluation ICP Labs, 16, sorted by mid range standard An evaluation of M3 solutions was conducted in ALP cycle 12, 16 labs participating. Miller, 2011 ID 1 K (ppm) Bottle #1 154 Bottle # Bottle # Bottle #4 451 Bottle #5 0 Labs #15 and #16 have high bias issues, all standards

Mehlich 3 Phosphorus Calibration Evaluation Miller, 2011 ALP Data base A performance report for M3 analyses was provided to each ALP participating laboratory.

U6288A U6304A U6322A U6333A U6336A U6356A U6718A U6791A U9814A U6816A Lab ID SlopeIntercept R2R2R2R2 Mehlich 3 ICP Phosphorus Evaluation Calibration Evaluation – 5 standards Miller, 2011 ALP Data base Ten of twelve reporting labs. Highlighted values indicate deviation from known calibration standards.

ID 1 M3 P SPEC (ppm) M3 P ICP (ppm) MeanStdMeanStd Bottle # * 1.0 Bottle # * 1.8 Mehlich 3 Phosphorus Evaluation Soil extract comparison Soil extract comparison Miller, Bottles #6 and #7 soil extracts of ALP soil SRS-0802 and SRS Mean values significant different at the 0.05 level based on twelve labs, triplicate. ALP Data base

Summary Miller, 2011 NRP associated with soils with low pH, high sand content and low silt contents. Location specific. Impact on recommendations and P index tool (PLAT). Evaluation of M3 P calibration standards show that 4 of 12 of labs have P calibrations that deviate greater than 5% from the known calibration slope. M3 K show that 5 of 16 labs show K calibration deviations greater than 5% from the known calibration slope.

Future work Miller, 2011 ALP will include Mehlich 1 elemental standard calibration solutions for Cycle 16, for P, K, Ca, Mg, Mn, and Zn. Solutions to be analyzed in triplicate for the evaluation of bias and precision.

Thank you for your time and attention