Low-Intensity Sprinkler for Evaluating Phosphorus Transport From Different Landscape Positions

High intensity rainfall causes a greater proportion of total phosphorus (P) in runoff to be particulate P (PP) thanlow-intensity rainfall. Traditional conservation practices have been implemented to control PP; however, dissolved ortho-P(DP) losses have been more difficult to reduce. Dissolved ortho-P losses may occur under different rainfall conditions, fromdifferent landscape locations, and from areas with different management histories than PP. To evaluate P lost in runoff frommultiple landscape positions simultaneously, a low-intensity sprinkler was developed. The design criteria included:<12.7-mm h-1 application rate; low operating pressure; fine drop size; uniform volume distribution; low cost; and ease oftransport, setup, and operation. An inverted full cone sprayer nozzle operating at 6.9 104 Pa, delivering 8.2 mm h-1, wasmounted within a 1.8- 1.8- 1.3-m polyvinyl chloride (PVC) pipe frame. The coefficient of uniformity for applicationwas 0.97 and the mean drop size diameter was 0.51 mm. In a field evaluation of the sprinkler, DP concentrations were greaterfrom the summit and backslope than from the footslope. Although there was no difference in DP or TP loads (concentration volume), the trend in DP load losses was greatest from the backslope (130 .g m-2), followed by the summit/shoulder(89 .g m-2), and then the footslope (28 .g m-2). The sprinkler performed effectively in field tests, but the results suggest thatmore research is necessary to better understand DP losses from different landscape positions under low-intensity rainfall.