Dissolved phosphorus (P) in runoff increases with an increase in soil test P, but slopes found for this relationship vary by an order of magnitude. A difference in clay content contributes to this variation. Experiments were conducted on Ultisols of 5 and 32% clay by incorporating poultry ( Gallus gallus domesticus ) litter and triple superphosphate (TSP) to create a wide range in Mehlich 3‐extractable phosphorus (M3P). Mehlich 3 P increased similarly for the two sources with rate of P applied, but the increase was greater as clay content decreased. Total P in runoff was measured and it was related primarily to the quantity of sediment. Dissolved P (mg L −1 ) was measured with simulated rainfall and it increased with an increase in M3P (mg dm −3 in the surface 15–20 cm of soil). The slope of dissolved P versus M3P was 0.0040 for the 5% clay soil and 0.0014 for the 32% clay soil. With these relationships, M3P would need to be 250 mg dm −3 at 5% clay and 714 mg dm −3 at 32% clay to result in 1.0 mg L −1 dissolved P in runoff. Dissolved P in samples of runoff collected from natural rainfall with automatic samplers was substantially less than that with simulated rainfall. Thus, there was a marked difference due to method of measurement as well as the difference noted due to day content. Both factors should be considered if attempting to predict the level of dissolved P in runoff from soil test data.
CITATION STYLE
Cox, F. R., & Hendricks, S. E. (2000). Soil Test Phosphorus and Clay Content Effects on Runoff Water Quality. Journal of Environmental Quality, 29(5), 1582–1586. https://doi.org/10.2134/jeq2000.00472425002900050027x
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