McGeehan, Steven L.; 1996 (December); Phosphorus Retention in Seasonally Saturated Soils Near
McCall, Idaho (Final Report), University of Idaho, Division of Soil Science, Moscow, Idaho; 54p
+ appendix.
A summary of four studies evaluating soil properties influencing, the sorption and transport
of phosphorus. Soil columns and conventional sorption measurement techniques were utilized. Soil types in the Cascade watershed were characterized. Sol] profile descriptions and chemical and physical characterizations were made for the four most extensive soil series in the McCall-Donnelly-Cascade area, namely Archbal, Donnel, Roseberry, and Kangas. Soils were sandy-loam to loamy sand (high sand content of >50% may be detrimental to phosphorus sorption at high flow rates). All characterized soils showed acidic pH values (near 4.5 to 5.0 at the surface, and increasing to 5.5 to 6.0 at -80" depth), indicative of conditions favorable for phosphorus sorption by aluminum and iron hydroxides. Organic (carbon) content of the characterized soils decreases with depth (Roseberry was highest with -3.3% at the surface to non-detectable levels at -80", Kangas was lowest with 1.3% at the surface and 0.02% at 84" but has only one sampling site so variability is unknown). Nitrogen levels (0.32% to non-detectable levels) showed high variability, and while some samples showed a decrease of nitrogen content with depth, in general there was no consistent, discernable trend with soil type or depth. Soluble phosphorus levels from all characterized soils exhibited concentrations of 0.02 to 0.24 mg/L with no discernable trends with increasing depth. It is not clear whether the phosphorus concentrations reported are mg/L of extract or have been normalized to reflect soil-water content. Phosphorus sorption capability was listed as showing a downward trend with decreasing depth but variability was high from sample to sample. Significant differences in phosphorus capacity were observed between soil samples flooded for different lengths of time. Flooded soils at cooler temperatures (I O'C) exhibited greater phosphorus sorption capacity than flooded soils at warmer temperatures (25'C). Results indicate that the enhanced sorption at I O'C does not translate to greater desorption of phosphorus. Roseberry and Archbal soil types were listed as exhibiting good phosphorus sorption characteristics, Kangas was listed as a poor sorption candidate due to large grain size and preferential flow tendencies. Donnel soil type was not specifically mentioned in the summary. Phosphorus sorption studies were performed under artificial laboratory conditions in columns and therefore may not accurately reflect performance in a natural environment.' Variability was high in most samples, and any trends observed may be an artifact of variability only. Extensive references listed are an exceptional resource.
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