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nium sulfate may have been delaying the adsorption of P applied as fertilizer, prolong- ing its mobility, and resulting in elevated P concentrations in leachate. Phosphate concen- trations quickly returned to previous levels in subsequent irrigation events. 3.5 2.5 3 2 E p 1.5 CL Phosphorus concentrations 1 1 o ow- in leachate were much higher than expected for all treat- 0 0.5 ments including unfertilized controls, while nitrate con- 0 0 centrations remained low 9 9/4/04 throughout the study. Aver- F Figure 4: Ave age N and P concentrations d during a ing Exper' were not influenced by fertil- c centrations for izer treatment at the fertilizer t tion event. Tr application rates used for this m monium sulfa study. Although short-term s superphospha spikes in concentration were observed immediately follow- ing fertilizer application, concentrations quickly returned to pre - fertilizer levels after subsequent irrigation events. phosphate concentrations measured in leachate nent 2. Data points represent average phosphate con - lysimeters of the same treatment following each irriga- eatments labeled by NP, P, and None correspond to am- te and superphosphate fertilizer applied simultaneously, to applied alone, and unfertilized, respectively. These results suggest that phosphorus leaching under irrigated turf may be more significant than previously thought. From a water quality perspective, phosphorus concentrations of 1.0 mg /L are quite high. Asa comparison, desir- able phosphorus levels for Front Range drink- ing water reservoirs are generally less than 0.05 mg /L. In the present study, residual phosphorus in the soil appears to be a significant source of "leachable" P since the leachate concentration was not greatly affected by the amount of phos- phorus added in fertilizer. Another significant finding is that the short -term mobility of phosphorus was increased by the ad- dition of ammonium sulfate fertilizer. This sug- gests that phosphorus loss from turf grass should be managed not only through controlling the amount of phosphorus fertilizer applied but also through managing nitrogen fertilizer application if ammonium sulfate is being used. Proper use of ammonium sulfate fertilizer may improve the efficiency of phosphorus fertilizers by increas- ing phosphorus availability and reducing the amount of phosphorus that must be applied. On the other hand increased mobility could result in movement of phosphorus beyond the root zone, increasing the possibility that unwanted phos- phorus could enter a surface stream or reservoir. In a parallel study, not reported here, we found that ammonium sulfate fertilizer also increased the mobility of phosphorus in surface runoff from irrigated turf. As nutrient leaching studies are site and situa- tion specific, so should be the development and application of appropriate and effective best management practices. More complete knowl- edge of nutrient leaching from a typical Colorado turf grass landscape and further understanding of the impact of ammonium sulfate and pH on phosphorus mobility will assist in developing more effective BMPs. Acknowlegements: Funding for this study was provided by the Colorado Agricultural Experi- ment Station Projects COL 00705 "Best Manage- ment Practices for Landscape Irrigation' and COL 00726 "Estimating Nutrient Loads for Water Quality Management ".