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C04VO —University Agricultural Experiment Station Leaching of Nitrogen and Phosphorus from Irrigated Turf by Jennifer E. Morgan, Graduate Research Assistant Department of Civil Engineering, Colorado State University utrophication of drinking water reservoirs, accelerated by nutrients, is a significant problem in Colorado, and urban land- scapes, including irrigated turf, are one of many potential sources of nutrient loading to reser- voirs. Previous nutrient transport studies have tended to be site and situation specific and have not often addressed nitrogen and phosphorus transport simultaneously. Conclusions of these studies often disagree, especially with regard to phosphorus transport. Leaching of phosphorus from turf grass is typically considered to be negli- gible due to the tendency of phosphorus to read- ily adsorb to soil particles. However, some recent studies have determined that substantial loads of phosphorus can be transported in leachate. To add some clarity to this issue, particularly with regard to Colorado conditions, the Colorado Agricultural Experiment Station has supported research at CSU to assess the influ- ence of fertilizer treatment on nitro- gen and phosphorus leaching from irrigated turf grass in a Colorado landscape. This article provides a snapshot of the study. Two separate leaching experiments were conducted using 24 sprinkler irrigated lysimeters (Figure 1) lo- cated at the Agricultural Engineer- ing Research Center at Colorado State University. Experiment 1 was designed to evaluate the effect of ammonium sulfate on N and P leaching and involved the applica- tion of ammonium sulfate fertilizer at rates of zero, 25.7 and 77 kg N ha -1. Experiment 2 was designed to evaluate the effect of both super- phosphate and ammonium sulfate fertilizers on N and P leaching and involved three different fertilizer treatments: no fertilizer, super- phosphate fertilizer (55 kg P ha -1) , and a combination of superphosphate (55 kg P ha -1) and ammonium sulfate (77 kg N ha -1) fertilizers. Irrigation was applied three times per week for both experiments, and leachate was collected following each irrigation event. Water drained from each lysimeter was measured for volume, and samples were analyzed for nitrate and phosphate concentrations. Total phosphorus concentrations, measured on occasion through- out the study, were typically equal to the concentrations measured for phosphate. Thus, it was appropriate to assume that phosphate measurements provided a reliable estimate of total phosphorus leaching. Figure 1. One of twenty -four lysim- eters used during the nutrient leach- ing experiments conducted at the Agricultural Engineering Research Center at Colorado State University. age nitrate concentration was observed for all three treatments. The trend was similar for both the fertilized and unfertilized lysimeters, suggesting that the increase in concentra- tion may have been due to higher irrigation rates at that point in time. The effect was more dramatic for several individual lysimeters and may have been the result of preferen- tial flow. As illustrated by the range of nitrate concen- trations for each fertilizer 4