ABSTRACT Phosphorus (P) fertilization is frequently needed for profitable crop production. Modified Morgan P (MMP) is a soil test P used to estimate plant available P in soils. The critical values of MMP for P fertilization and maintenance recommendations are based on the P concentrations measured by a common colorimetric molybdenum blue method although other P quantification methods have also been used for MMP measurements. In this study, we collected 120 surface soil samples of Caribou Sandy loam under potato cultivation or its rotation crops from Maine, USA, and 72 soil samples of Cecil sandy loam with cotton/corn crops under conventional tillage and no-till management with chemical and poultry litter fertilization in Georgia, USA. The MMP levels in all 192 dry samples were greater when they were measured by an inductively coupled plasma (ICP)-based method, compared to the corresponding data produced from colorimetry. Our results show the two sets of data were positively and significantly correlated (r = 0.93, P < 0.001). In average, the ICP-based MMP level of the 192 samples was 23.3 mg P kg–1 with standard deviation of 12.9, compared to the average of colorimetric MMP level of 14.9 mg P kg–1 with standard deviation of 8.8. Based on the observations in this work, both colorimetric and ICP-based methods can be used for P fertilizer recommendation, but a conversion factor should be applied for ICP data as the current recommendation systems are based on colorimetric M&R data.
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Z. He, H. Zhang, O. Olanya, J. Frantz and R. Larkin, "Differences in Modified Morgan Phosphorus Levels Determined by Colorimetric and Inductively Coupled Plasma Methods," Open Journal of Soil Science, Vol. 2 No. 3, 2012, pp. 256-262. doi: 10.4236/ojss.2012.23030.
 M. S. Erich, C. B. Fitzgerald and G. A. Porter, “The Effect of Organic Amendments on Phosphorus Chemistry in a Potato Cropping Systems,” Agriculture, Ecosystems & Environment, Vol. 88, No. 1, 2002, pp. 79-88.
 T. Ohno, B. R. Hoskins and M. S. Erich, “Soil Organic Matter Effects on Plant Available and Water Soluble Phosphorus,” Biology and Fertility of Soils, Vol. 43, No. 6, 2007, pp. 683-690. doi10.1007/s00374-006-0150-1
 W. E. Jokela, F. R. Magdoff and R. P. Durieux, “Improved Phosphorus Recommendations Using Modified Morgan Phosphorus and Aluminum Soil Tests,” Communications in Soil Science and Plant Analysis, Vol. 29, No. 1998, pp. 1739-1749. doi10.1080/00103629809370064
 J. R. Heckman, et al., “Soil Test Calibration for Predicting Corn Response to Phosphorus in the Northeast USA,” Agronomy Journal, Vol. 98, No. 2, 2006, pp. 280-288.
 Z. Q. He and C. W. Honeycutt, “A Modified Molybdate Blue Method for Orthophosphate Determination Suitable for Investigating Enzymatic Hydrolysis of Organic Phosphates,” Communications in Soil Science and Plant Analysis, Vol. 36, No. 9-10, 2005, pp. 1373-1383.
 M. D. Ron Vaz, A. C. Edwards, C. A. Shand and M. S. Cresser, “Phosphorus Fractions in Soil Solution: Influence of Soil Acidity and Fertiliser Additions,” Plant and Soil, Vol. 148, No. 2, 1993, pp. 175-183.
 J. J. Pittman, H. Zhang, J. L. Schroder and M. E. Payton, “Differences of Phosphorus in Melich 3 Extracts Determined by Colorimetric and Spectroscopic Methods,” Communications in Soil Science and Plant Analysis, Vol. 36, No. 11-12, 2005, pp. 1641-1659.
 A. P. Mallarino, “Field Calibration for Corn of the Mehlich-3 Soil Phosphorus Test with Colorimetric and Inductively Coupled Plasma Emission Spectroscopy Determination Methods,” Soil Science Society of America Journal, Vol. 68, No. 6, 2003, pp. 1928-1934.
 F. J. Sikora, P. S. Howe, L. E. Hill, D. C. Reid and D. E. Harover, “Comparison of Colorimetric and ICP Determination of Phosphorus in Mehlich 3 Soil Extracts,” Communications in Soil Science and Plant Analysis, Vol. 36, No. 7-8, 2005, pp. 875-887. doi10.1081/CSS-200049468
 N. Ziadi, G. Belanger, B. Gagnon and D. Mongrain, “Mehlich 3 Soil Phosphorus as Determined by Colorimetry and Inductively Coupled Plasma,” Communications in Soil Science and Plant Analysis, Vol. 40, No. 1-6, 2009, pp. 132-140. doi10.1080/00103620802649377
 M. R. Hart and P. S. Cornish, “Comparison of Bicarbonate-Extractable Soil Phosphorus Measured by ICP-AES and Colourimetry in Soils of South-Eastern New South Wales,” Soil Research, Vol. 47, No. 7, 2009, pp. 742-746.
 Z. Q. He, C. W. Honeycutt, M. Olanya, R. P. Larkin and J. H. Halloran, “Soil Test Phosphorus and Microbial Biomass Phosphorus in Potato Field,” Journal of Food Agriculture and Environment, Vol. 9, No. 1, 2011, pp. 540-545.
 Z. Q. He, C. W. Honeycutt and H. Zhang, “Elemental and Fourier Transform Infrared Spectroscopic Analysis of Water and Pyrophosphate Extracted Soil Organic Matter,” Soil Science, Vol. 176, No. 4, 2011, pp. 183-189.
 Z. Q. He, D. M. Endale, H. H. Schomberg and M. B. Jenkins, “Total Phosphorus, Zinc, Copper, and Manganese Concentrations in Cecil Soil through Ten Years of Poultry Litter Application,” Soil Science, Vol. 174, No. 12, 2009, pp. 687-695.
 H. H. Schomberg, D. M. Endale, M. Jenkins, R. R. Sharpe, D. S. Fisher, M. L. Cabrera and D. V. McCracken, “Soil Test Nutrient Changes Induced by Poultry Litter under Conventional Tillage and No-Tillage,” Soil Science Society of America Journal, Vol. 73, No. 1, 2009, pp. 154-163.
 F. S. Watanabe and S. R. Olsen, “Test of an Ascorbic Acid Method for Determining Phosphorus in Water and NaHCO3 Extracts from Soil,” Soil Science Society of America Journal, Vol. 29, No. 6, 1965, pp. 677-678.
 W. A. Dick and M. A. Tabatabai, “Determination of Orthophosphate in Aqueous Solutions Containing Labile Organic and Inorganic Phosphorus Compounds,” Journal of Environmental Quality, Vol. 6, No. 1, 1977, pp. 82-85.
 E. K. Bunemann, “Enzyme Additions as a Tool to Assess the Potential Bioavailability of Organically Bound Nutrients,” Soil Biology and Biochemistry, Vol. 40, No. 9, 2008, pp. 2116-2129. doi10.1016/j.soilbio.2008.03.001
 Z. Q. He and C. W. Honeycutt, “Enzymatic Hydrolysis of Organic Phosphorus,” In: Z. He, Ed., Environmental Chemistry of Animal Manure, Nova Science Publisher, New York, 2011, pp. 253-274.
 Z. Q. He, D. C. Olk and B. J. Cade-Menun, “Forms and Lability of Phosphorus in Humic Acid Fractions of Hord Silt Loam Soil,” Soil Science Society of America Journal, Vol. 75, No. 5, 2011, pp. 1712-1722.
 Z. Q. He, D. C. Olk, C. W. Honeycutt and A. Fortuna, “Enzymatically and Ultraviolet-Labile Phosphorus in Humic Acid Fractions from Rice Soils,” Soil Science, Vol. 174, No. 2, 2009, pp. 81-87.
 P. H. Pagliari and C. A. M. Laboski, “Investigation of the Inorganic and Organic Phosphorus Forms in Animal Manure,” Journal of Environmental Quality, Vol. 41, No. 3, 2012, pp. 901-910. doi10.2134/jeq2011.0451
 Z. Q. He, H. L. Zhang and M. C. Zhang, “Irrigation-Induced Changes in Phosphorus Fractions of Caribou Sandy Loam Soil under Different Potato Cropping Systems,” Soil Science, Vol. 176, No. 12, 2011, pp. 676-683.
 D. Styles and C. Coxon, “Laboratory Drying of Organic-Matter Rich Soils: Phosphorus Solubility Effects, Influence of Soil Characteristics, and Consequences for Environmental Interpretation,” Geoderma, Vol. 136, No. 1-2, 2006, pp. 120-135.
 H. L. Zhang, S. Kariuki, J. L. Schroder, M. E. Payton and C. Focht, “Interlaboratory Validation of the Mehlich 3 Method for Extraction of Plant-Available Phosphorus,” Journal of AOAC International, Vol. 92, No. 1, 2009, pp. 91-102.