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

• Published in: Soil Science Society of America journal Vol. 66; no. 6; pp. 2016 - 2032
• Main Authors: Sims, J. T., Maguire, R. O., Leytem, A. B., Gartley, K. L., Pautler, M. C.
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.11.2002; Soil Science Society of America; American Society of Agronomy
• Subjects: Agricultural land; Agricultural runoff; Biological and medical sciences; Crop yield; Fundamental and applied biological sciences. Psychology; Groundwater; Leachates; Leaching; Natural resources; Nonpoint source pollution; Phosphorus; Pollution; Resource conservation; Soil testing; Soils; Water quality; Atlantic states; USA, Mid-Atlantic Region; USA, Delaware
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2002.2016

Laws and guidelines limiting P applications to cropland based on soil P exist in the Mid‐Atlantic USA because of water quality concerns. We evaluated Mehlich 3 (M3) as an environmental soil P test using 465 soils typical to the Mid‐Atlantic region and found M3‐P accurately predicted water soluble P (WSP), desorbable P (Fe oxide strip P [FeO‐P]), and total sorbed P (oxalate P). The M3‐P saturation ratio (M3 [P/(Al+Fe)]) was linearly related to the well‐established oxalate P saturation method (DPSox) and a M3 [P/(Al+Fe)] range of 0.10 to 0.15 corresponded to reported environmental limits for DPSox (25–40%). Rainfall simulation and column leaching studies showed M3 [P/(Al+Fe)] predicted runoff and leachate P concentrations better than M3‐P. We suggest consideration of the following approach now used in Delaware for agri‐environmental interpretation of M3‐P and M3 [P/(Al+Fe)]: (i) Below optimum (crop response likely; M3‐P ≤ 50 mg kg−1; M3 [P/(Al+Fe)] < 0.06); (ii) Optimum (economic response to P unlikely, recommendations for P rarely made; M3‐P = 51–100 mg kg−1; M3 [P/(Al+Fe)] = 0.06–0.11); (iii) Above Optimum (soil P will not limit crop yields, no P recommended; M3‐P > 100 mg kg−1; M3 [P/(Al+Fe)] > 0.11); (iv) Environmental (implement improved P management to reduce potential for nonpoint P pollution—in Delaware M3‐P > 150 mg kg−1; M3 [P/(Al+Fe)] > 0.15 is now used). (v) Natural Resource Conservation (no P applied even if the potential water quality impact is low to conserve P, a finite natural resource).