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Modeling Phosphorus Transfer between Labile and Nonlabile Soil Pools

Updating the EPIC Model

^a USDA-ARS, Pasture Systems and Watershed Management Research Unit, Building 3702, Curtin Rd., University Park, PA 16802-3702
^b Dep. of Plant Environ. Sci., Norwegian Univ. Life Sci., N-1432 Aas, Norway

View larger version (22K): [in a new window]   Fig. 1. Example of measured decreases in (a) labile P measured with Fe-oxide strips, and calculated (b) PSC values, and (c) P sorption rate values for one soil of Pautler and Sims (1998).

View larger version (30K): [in a new window]   Fig. 2. For soils of Indiati et al. (1999), Javid and Rowell (2002), Robinson and Sharpley (1996), Sharpley (1982), Sharpley et al. (1989), and Pautler and Sims (1998), relationship between (a) calculated A and B values where only labile P is measured, or (b) where labile, Olsen, and Mehlich-3 P are measured. (c) Relationship between calculated A and PSC values.

View larger version (22K): [in a new window]   Fig. 3. Examples of (a) the method used to match predicted P moved from Active to Labile P to measured sequentially extracted Fe-oxide strip P and (b) the decline in calculated P desorption rate factors for one soil of Sharpley (1996). (c) Relationship between soil PSC values and calculated base values in exponential equations describing decreases in P desorption rate factors with time for data of Indiati (1998), Indiati and Sharpley (1996), Maguire et al. (2000), McDowell and Sharpley (2002), Sharpley (1996), and Siddique and Robinson (2004).

View larger version (26K): [in a new window]   Fig. 4. For nine soils from the Eastern USA subjected to various P additions and incubation times, the relationship between measured Fe-oxide strip P and predicted soil labile P using (a) dynamic or (b) constant 0.1 sorption rate factors.

View larger version (33K): [in a new window]   Fig. 5. For nine soils from the Eastern USA subjected to various P additions and incubation times, the relationship between measured sequentially extracted Fe-oxide strip P and predicted soil labile P using (a) constant 0.1, (b) constant 0.6, or (c) dynamic desorption rate factors.