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The sorption of soluble phosphorus by soil material during transport in runoff from cropped and grassed watersheds

Sharpley, A.N., Menzel, R.G., Smith, S.J., Rhoades, E.D., Olness, A. E.
Journal of environmental quality 1981 v.10 no.2 pp. 211
sorption, phosphorus, agricultural runoff, agricultural watersheds, crop production, grasslands, grassland soils, soil chemical properties, sediments, field experimentation, linear models, rain, soil transport processes, soil physical properties, phosphorus fertilizers, leaching, vegetation cover, Great Plains region
The adsorption of soluble P by surface soil and suspended sediment material during transport in surface runoff under field and simulated laboratory conditions was investigated. The soluble P concentration of surface runoff from several Southern Plains cropped and grassed watersheds decreased with an increase in sediment concentration, A linear inverse relationship between soluble P and sediment concentration was significant over a wide range in sediment concentration. The slope values of the relationship were similar for different watersheds on the same major soil type. Using soil from these watersheds in simulated surface runoff, sorption of soluble P added in rainfall was found to occur during transport. The magnitude of this sorption was more closely related to the sorptive capacity of the sediment in the surface runoff than to that of the surface soil material. The results suggest that for unfertilized watersheds and for watersheds where fertilizer P is incorporated into the surface soil, away from the zone of immediate removal in surface runoff, the leaching of P from the vegetative cover can contribute significant amounts of soluble P to runoff, and that soil material may act as a P sink rather than a P source.