Phosphorus Losses from Four Agricultural Watersheds on Missouri Valley Loess
1973
Schuman, G. E. | Spomer, R. G. | Piest, R. F.
Phosphorus losses from four field-size experimental watersheds at Treynor, Iowa, were measured during 1969, 1970, and 1971. A contour-planted corn watershed and a pasture watershed were fertilized at the recommended P rate (39 kg/ha). A level-terraced and a second contour-planted corn watershed were fertilized at 2.5 times this rate. At the high level of P fertilization, phosphorus loss by surface runoff from the contour-planted corn watershed was 0.495 kg/ha in 1969, 1.034 kg/ha in 1970, and 2.130 kg/ha in 1971. Level terraces greatly reduced P loss by reducing runoff and erosion. Water samples for all runoff events taken above the overfall of each watershed gully contained considerably more inorganic P in solution than samples taken at the weir site, 70 to 230 m downstream. This reduction in solution P was caused by the adsorption of P by the additional suspended soil material entering the stream from gully erosion.
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