The Effect of Storm Interval on the Transport of Soluble Phosphorus in Runoff

The effect of varying the interval between events on the transport of soluble phosphorus (P) in runoff was evaluated under simulated rainfall conditions. A decrease in soluble P concentration was observed during each runoff event although initial concentrations increased as the interval between events was decreased from 1 day to 5 min (0.027–0.033 mg/liter and 0.020–0.028 mg/liter for Bernow fine sandy loam and Woodward loam soils). This was attributed in part to a movement of soil water down the profile following cessation of runoff, resulting in a decrease in the surface soil of the “pool” of soluble P susceptible to transport in runoff. In contrast, a marked increase in the mean concentration of soluble P in runoff was observed as event interval increased from 1 to 6 days (0.018–0.026 mg/liter and 0.011–0.041 mg/liter for Bernow and Woodward soils). This increase was found to be related to the phosphatase enzyme activity of the five soils studied and could thus, be partially attributed to mineralization of organic P.