Monday, 7 November 2005
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Phosphorus Availability on a Pasture Toposequence: Effect of Available Water, Soil Temperature and Phosphorus Rate.

Louis M. McDonald, Rafif Srour, and W.B. Bryan. WVU, Div.of Plant & Soil Sci., Morgantown, WV 26506-6108

The spatial and temporal variability in soil P concentration was investigated along a pasture toposequence. Soil samples were collected from three locations (summit, backslope and footslope), and enriched with four P concentrations (0, 25, 50, 100 mg P kg-1). These samples were incubated in the dark in a growth chamber for 30 days at three different temperatures (15, 25 and 35oC) and three different moisture levels (10%, 50% and 90% wt/wt). At 10 days interval, 1 ml of soil solution was sampled and total equilibrium P determined. After 30 days incubation, subsamples of each treated soil sample were then equilibrated with different amounts of bicarbonate saturated anion exchange resins for 72 hrs, afterwhich the soil solution P and the amount of P sorbed on the resins were determined. The P release capacity of all samples was generally low (< 0.537 mg L-1) and varied significantly between locations, with initial P content, temperature and time, but not with moisture content.

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