Prediction of Water-Extractable Phosphorus Content of Soil Following a Phosphorus Addition
1982
Sharpley, Andrew N.
The effect of time on the water-extractable P content (PX) of surface soil (0–10 cm) following a P addition (PA) was investigated in the laboratory using 20 soils from 14 states. The soils were incubated with P equivalent to 0-, 25-, 50-, and 100-kg/ha additions and the water-extractable P content and soluble P concentrations of runoff from the soils determined at frequent intervals. Water-extractable P decreased in the first 2 weeks after P addition; following this PX remained fairly constant. Water-extractable soil P content was linearly related to PA at any given time after the addition. The slope of this relationship decreased logarithmically with time after a P addition. In the first 2 weeks after P addition, the slope of the relationship between PX and PA could be predicted from percent clay content or P sorption capacity of the soil. Using these simple relationships, an improved prediction of the amount of soluble P available for transport in surface runoff from fallow soil can be made from limited extractable soil P data.
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