Potential of an Eroding Urban Soil for the Phosphorus Enrichment of Streams: I. Evaluation of Methods
1972
Ryden, J. C. | Syers, J. K. | Harris, R. F.
Eroding noncalcareous and calcareous soil horizons sampled on an urban development site sorbed a varying proportion of added inorganic phosphate (P). At an added P level of 600 µg P/liter (30 µg P/g soil in 50 ml of 0.1M NaCI), the A1 horizon showed a net release of P whereas the B1 and 3C1 horizons sorbed 96 and 53% of the added P, respectively. The appreciable release of P from the A1 horizon is attributed to the presence of a small amount of a moderately soluble P fertilizer-soil reaction product. In simulated stream systems employing a solution/soil ratio of 1000:1, initial added P concentrations of 0 and 50 µg P/liter, and adequate aeration, approximately 50% of the final P concentration was attained in less than 3 hours. Release of P (50 µg P/liter) from the A1 horizon was independent of the initial P concentration. The B1 horizon released 10 µg P/liter, twice that released by the 3C1 horizon, whereas these two horizons sorbed approximately equal amounts of added P. In a system containing a 1:1 mixture of the A1 and B1 horizons, the amount of P released by the A1 in the presence or absence of added P was greater than that capable of being sorbed by the B1 horizon. Initial P concentrations were shown to be more important than the solution/soil ratio in determining the extent of uptake and release of P by the soil horizons. The use of a 400:1 solution/soil ratio and low levels of added P (0 to 200 µg P/liter) provides a useful basis for developing a routine test for evaluating the potential of eroding soils for the P enrichment of streams.
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