Chapter 6 The Effects of Soil Phosphorus and Nitrogen and Phosphorus Fertilization on Phosphorus Runoff Losses from Turfgrass

摘要

Turfgrass accounts for a large percentage of land in urban and suburban areas and thus, it is important to understand the effects of turfgrass on surface water quality. Runoff from natural and simulated rain events was collected from a cool season turfgrass mixture on an undisturbed sandy loam soil for two years. Field plots with runoff collectors had different soil P levels as a result of prior fertilization practices. The treatments for this study were fertilizer application levels and included no fertilizer, nitrogen (N) only, phosphorus (P) only, or both N and P. Runoff volumes were measured and a subsample was saved for dissolved and total P analysis. Phosphorus losses were 0.05% of fertilizer applied for both dissolved and total P. Low mass losses of dissolved P were observed (<0.05 kg ha~(-1) yr~(-1)) and can be attributed to the small amount of precipitation that became runoff. Application of N or P did not affect the amount of runoff from natural or simulated events. Fertilization with N or P increased the concentration of P in the runoff to a similar extent. Soil P levels had no effect on runoff P concentrations or mass losses, despite Morgan extractable soil P levels ranging from 3.7 to 35.6 mg kg~(-1) at the 0-5 cm depth. The simulated events supported the data observed from the natural events in most cases. Significant differences in infiltration rate among treatments were found on 2 of the 6 simulation dates.Significant differences in P loss were only observed when no precipitation fell between a fertilization event and a simulated runoff event. The results of this study suggest that fertilization of established turfgrass does not result in a reduction in runoff volume when visual quality responses to N are similar to those observed in this study. Since increased P runoff concentrations were associated with N and P fertilization, the environmental impacts of turfgrass could be reduced by withholding or limiting N and P fertilizers under these conditions. Soil P level was not a good indicator of P concentration in runoff for this sandy loam and across the range of soil P levels seen in this study. Thus, predictions of runoff P loss based on soil P levels may be misleading or inaccurate for turfgrass areas.