Two 30 minute runoff events were conducted where surface water samples were collected at 10 minute intervals and analyzed for soluble P. The first surface runoff event occurred immediately after PL application to evaluate the initial effects of the gypsum amendments; the second runoff event occurred four weeks later to evaluate the long-term effects. The greatest concentration of soluble P was observed in the runoff event that occurred immediately following the PL application. Gypsum applied to grass buffer strips was effective in reducing soluble P concentrations at the highest rate in surface runoff, while the untreated buffer strip was somewhat effective. In the second runoff event, although the concentration of soluble P was greatly reduced, the effect of gypsum had diminished. These results show that gypsum is most effective in reducing the initial losses of soluble P from PL application when applied to grass buffer strip.

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