A protocol for conducting rainfall simulation to study soil runoff

Authors: KIBET, LEONARD - University Of Maryland Eastern Shore (UMES); Saporito, Louis - Lou; ALLEN, ARTHUR - University Of Maryland Eastern Shore (UMES); MAY, ERIC - University Of Maryland Eastern Shore (UMES); Kleinman, Peter; HASHEM, FAWSY - University Of Maryland Eastern Shore (UMES); Bryant, Ray

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2013
Publication Date: 4/3/2014
Citation: Kibet, L.C., Saporito, L.S., Allen, A.L., May, E.B., Kleinman, P.J., Hashem, F.M., Bryant, R.B. 2014. A protocol for conducting rainfall simulation to study soil runoff. Journal of Visualized Experiments. (86), e51664, doi:10.3791/51664.

Interpretive Summary: Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. Rainfall simulators that are designed to deliver raindrops of similar size and velocity as natural rainfall facilitate the study of contaminant transport in soil runoff. However, in order to compare results across multiple studies, a standardized protocol for conducting rainfall simulation is needed. The purpose of this study was to produce and publish a video that will instruct others on the proper protocol for using a rainfall simulator. As a case study, the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea was characterized. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results demonstrate the importance of controlling for antecedent soil moisture content in rainfall simulation studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Rainfall simulation studies conducted under this standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.

Technical Abstract: Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hours after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been pre-wetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.