Module 4: Recent Developments in Techniques for Evaluating Phosphorus Release from Soils


Lecture 1: Degree of P saturation & the P saturation ratio: Theory and calculations

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Describes why the degree of P saturation ratio (DPS) is used and how to calculate it, including the extractants that can be used for DPS calculations. Explains the P saturation ratio (PSR), the preferred extractants, and molar calculations. Describes the change point concept and the difference between soil test phosphorus (STP) and PSR.

  • References
    • Beck et al., 2004. Soil Sci. Soc. Am. J. 68:1762−1771.
    • Breeusma, A and S. Silva. 1992. Phosphorus fertilization and environmental effects in The Netherlands and the Po region (Italy). Rep. 57. Winard Staring Center, Wageningen, The Netherlands.
    • Freese, D., R. Lookman, R. Merckx, and W.H. van Riemsdijk. 1995. New method for assessment of long-term phosphate desorption from soils. Soil Sci. Soc. Am. J. 59:1295–1300.
    • Khiari, L., L.E. Parent, A. Pellerin, A.R.A. Alimi, C. Tremblay, R.R. Simard, and J. Fortin. 2000. An agri-environmental phosphorus saturation index for acid coarse-textured soils. J. Environ. Qual. excessive losses of P from agricultural land continue to 29:1561–1567
    • Maguire, R.O., and J.T. Sims. 2002. Soil testing to predict phosphorus leaching. J. Environ. Qual. 31:1601−1609.
    • Nair, V.D., and D.A. Graetz. 2002. Phosphorus saturation in Spodosols impacted by manure. J. Environ. Qual. 31:1279-1285.
    • Nair, V.D., K.M. Portier, D.A. Graetz, and M.L. Walker. 2004. An environmental threshold for degree of phosphorus saturation in sandy soils. J. Environ. Qual. 33:107–113.
    • Paulter, M.C., and J.T. Sims. 2000. Relationships between soil test phosphorus, soluble phosphorus, and phosphorus saturation in Delaware soils. Soil Sci. Soc. Am. J. 64:765-733.
    • Sims, J.T., R.O. Maguire, A.B. Leytem, K.L. Gartley, and M.C. Pautler. 2002. Evaluation of Mehlich 3 as an agri-environmental soil phosphorus test for the mid-Atlantic United States of America. Soil Sci. Soc. Am. J. 66:2016−2032.



Lecture 2: Degree of P saturation and the P saturation ratio: Examples from literature

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Gives examples from the literature of reported change points, including those for Florida soils, for the spodic horizon and for wetland soils, and summarizes threshold PSR values from the literature for soils globally and in Florida.



Lecture 3: The P saturation ratio (PSR) and isotherm parameters

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Reviews isotherm models and their components, including equilibrium P concentration and Smax under aerobic and anaerobic conditions, and relates isotherm parameters to soil test data.



Lecture 4: Soil phosphorus storage capacity (SPSC)

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Describes the soil P storage capacity (SPSC), a new indicator for evaluating P release from soils, how it is used, how to calculate it for A and E horizons, for the Bh horizon and for the spodic horizon, discusses the relationship between SPSC and WSP for wetland soils, and explains the application of PSR and SPSC in risk assessment of soils.



Lecture 5: Relating recently developed techniques (PSR & SPSC) to existing data

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Reviews the QPT procedure and the relationship between QPT and Mehlich 1-P and PSR, discusses the effects of biochar application to a low-P retentive soil and a high-P retentive soil using SPSC, and describes how to use the recently developed technique to explain the Florida-P index, with suggested modifications to the Florida-P index based on the SPSC.

Next - Module 5: Phosphorus Storage and Release from P-impacted Soils