title: A protocol for conducting rainfall simulation to study soil runoff.
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 hr 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 prewetted 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.
authors.affiliation: Department of Agriculture, Food and Resource Sciences, University of Maryland Eastern Shore.
authors.forename: Leonard C
authors.initials: LC
authors.lastname: Kibet
authors.affiliation: Pasture Systems and Watershed Management Research Unit, USDA - Agricultural Research Service.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Saporito
authors.affiliation: Department of Agriculture, Food and Resource Sciences, University of Maryland Eastern Shore.
authors.forename: Arthur L
authors.initials: AL
authors.lastname: Allen
authors.affiliation: Department of Natural Sciences, University of Maryland Eastern Shore.
authors.forename: Eric B
authors.initials: EB
authors.lastname: May
authors.affiliation: Pasture Systems and Watershed Management Research Unit, USDA - Agricultural Research Service.
authors.forename: Peter J A
authors.initials: PJ
authors.lastname: Kleinman
authors.affiliation: Department of Agriculture, Food and Resource Sciences, University of Maryland Eastern Shore.
authors.forename: Fawzy M
authors.initials: FM
authors.lastname: Hashem
authors.affiliation: Pasture Systems and Watershed Management Research Unit, USDA - Agricultural Research Service; ray.bryant@ars.usda.gov.
authors.forename: Ray B
authors.initials: RB
authors.lastname: Bryant
mesh_terms: D016573:Agrochemicals / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods; D008962:Models, Theoretical; D011891:Rain; D012987:Soil / Q000737:chemistry*; D014508:Urea / Q000737:chemistry*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D016573:Agrochemicals; D012987:Soil; D014874:Water Pollutants, Chemical; D014508:Urea
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