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Evaluation of Mehlich 3 as an Agri-Environmental Soil Phosphorus Test for the Mid-Atlantic United States of America

Dep. Plant and Soil Sciences, Univ. Delaware, Newark, DE 19717-1303. Paper No. 1708 in the journal series of the Delaware Agric. Expt. Stn

View larger version (33K): [in a new window]   Fig. 1. Comparison of the forms and distribution of soil P in the profiles of cropped and forested soils from four poultry farms in southern Delaware. (a) Changes in Mehlich 3 P with depth in the soil profile; (b) Changes in degree of P saturation by the oxalate method (DPSox) in the soil profiles; (c) Relationships between Mehlich 3 P in topsoils and DPSProfile and water soluble P (WSP) at the 60- to 90-cm soil depth.

View larger version (32K): [in a new window]   Fig. 2. Relationships between Mehlich 3 P and (a) water soluble P (WSP), (b)Fe oxide strip P (FeO-P), and (c) degree of P saturation via the oxalate method (DPSox) for all 465 soils used in the study. Dashed vertical lines represent the agronomic critical value for Melich 3-P (50 mg kg-1) and dashed horizontal lines represent the corresponding values for WSP, FeO-P, and DPSox, as derived from the linear regression equations in each graph.

View larger version (25K): [in a new window]   Fig. 3. Relationships between Mehlich 3 and acid ammonium oxalate extractable (a) P, (b) Al, and (c) Fe, for all 465 soils used in the study. Correlation coefficients in each graph are based on the entire data set.

View larger version (25K): [in a new window]   Fig. 4. Relationships between (a) Mehlich 3 [P/(Al+Fe)] and degree of P saturation via the oxalate method (DPSox) and (b) Mehlich 3 (P/Al) and Mehlich 3 [P/(Al+Fe)] for all 465 soils used in the study.

View larger version (20K): [in a new window]   Fig. 5. Relationships between Mehlich 3 [P/(Al+Fe)] and (a) dissolved reactive P (DRP) in runoff from soils in a rainfall simulation runoff box study (data are all reps of all 17 soils used in the study); and (b) dissolve reactive P (DRP) in leachate from undisturbed soil columns (reproduced from Maguire and Sims, 2002). Note that r2 values apply to the entire split-line model, not individual segments.

View larger version (17K): [in a new window]   Fig. 6. Relationships between Mehlich 3 P and (a) dissolved reactive P (DRP) in runoff from soils in a rainfall simulation runoff box study (data are all reps of all 17 soils used in the study); and (b) DRP in leachate from undisturbed soil columns. Note that r2 values apply to the entire split-line model, not individual segments.

View larger version (35K): [in a new window]   Fig. 7. Frequency distribution of degree of P saturation via the oxalate method (DPSox) (a, b, c) and Mehlich 3 [P/(Al+Fe)] (d, e, f) in the below optimum, optimum, and above optimum Mehlich-3-P ranges. Data are for agricultural topsoils only (n = 335). Median, mean, and standard errors apply to DPSox and Mehlich 3 [P/(Al+Fe)] data in each interpretive category.

View larger version (34K): [in a new window]   Fig. 8. Frequency distribution of FeO-P (a, b, c) and water soluble P (WSP) (d, e, f) in the below optimum, optimum, and above optimum Mehlich-3-P ranges. Data are for agricultural topsoils only (n = 335). Median, mean, and standard errors apply to FeO-P and WSP data in each interpretive category.