Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2003
Publication Date: 12/20/2003
Citation: Sharpley, A.N., Kleinman, P.J.A. 2003. Effect of rainfall simulator and plot scale on overland flow and phosphorus transport. Journal of Environmental Quality. 32:2172-2179. Interpretive Summary: Phosphorus, an essential element for crop and animal production, can also accelerate freshwater eutrophication. However, there is not enough information available on how soil phosphorus levels affect loss of phosphorus in runoff, on which to base phosphorus application strategies that are now required by recent nutrient management regulations. Thus, portable rainfall simulators and small temporary plots are being used to study the relationship between soil management and phosphorus loss in runoff. This approach reduces the time, expense, and uncertainty involved in natural rainfall and field-sized experiments. We conducted a study to compare runoff processes and phosphorus losses using a range in plot and field sizes (from 2 square meters to 6 hectares) and with simulated (man-made) and natural rainfall. It was found that while absolute losses of phosphorus varied with field size and between man-made and natural rainfall, processes governing the release of phosphorus from soil and transport in runoff were the same. It is therefore possible to use small temporary plots and man-made rainfall that is generated by portable equipment to identify soil management effects on phosphorus loss and determine environmental thresholds for soil phosphorus required by farm nutrient management planners.
Technical Abstract: Rainfall simulation experiments are used widely to study erosion and contaminant transport in overland flow. As little information is available to support the use of small plots and rainfall simulators, we compared dissolved reactive phosphorus (DRP) and particulate P (PP) transport in overland flow from 2- and 10.7-m long plots and with published watershed scale data. Simulated rainfall (7.5 cm h-1) generated more overland flow from 2- (20 L/m2) than from 10.7-m long plots (10 L/m) established in grass, no-till corn, and recently-tilled fields, as a function of varying source areas of overland flow between plot sizes. Although overland flow DRP was greater from 2- (0.50 mg/L) than 10.7-m long plots (0.35 mg/L), the relationship between DRP and Mehlich-3 soil P (as defined by regression slope) was similar for both plots sizes and for published watershed data (0.002 for grassed, 0.003 for no till, and 0.010 for tilled sites). Conversely, sediment, PP, and total P (TP) concentrations and selective transport of soil fines (<2 µm) were significantly lower from 2- than 10.7-m long plots. However, slopes of the logarithmic regression between P enrichment ratio and sediment discharge were similar (0.281 - 0.301) for 2- and 10.7-m long plots and published watershed data. While concentrations and loads of P change with plot scales, processes governing DRP and PP transport in overland flow are consistent, supporting the limited use of small plots and rainfall simulators to assess environmental soil P thresholds as a function of soil type and management.