Water-soluble phosphorus as affected by soil to extractant ratios, extraction times, and electrolyte

One of the most important nutrients for plant production is phosphorus (P). However mismanagement of fertilizer or manure can lead to P build-up in surface soils and elevate P loss in runoff possibly resulting in accelerated eutrophication. Concern of excess P in runoff has increased interest in water-soluble soil P and its use in determining potential for runoff P loss. Several variations of this procedure are currently in practice causing difficulty in comparing research findings. This study evaluated the effectiveness of several common variations of the water-soluble P procedures. Water-soluble soil P was analyzed for 10 soils using four different soil to solution ratios (1:2, 1:5, 1:10, 1:50) and four extraction times (10, 30, 60, and 900 min.). In addition, calcium chloride solutions (0.005 M, 0.01 M, 0.02 M) were compared to deionized water (DW) as extractant. The average amount of water-soluble P increased with wider soil to Solution ratio, whereas the extraction time had no effect on the amount of P extracted. Water-soluble P extracted by the various soil to solution ratios and extraction times was significantly related to Mehlich 3 P (r(2) > 0.83; p < 0.001). These findings suggest that a standardized procedure be used for water-soluble P analysis.