Saturday, 15 July 2006
139-39

Phosphorus Sorption Related to Extractable Aluminum and Iron in Some Podzols (Spodosols) in Michigan, USA.

Antoni Szafranek, Dept of Soil Science and Soil Conservation, Warsaw Univ of Technology, Plac Politechniki 1, Warsaw, 00-661, Poland and Delbert L. Mokma, Dept of Crop and Soil Sciences, Michigan State Univ, East Lansing, MI 48824.

Excessive phosphorus loss from soils leads to eutrophication of surface waters and is a growing concern in many parts of the world. Transport of P with water in soils depends primarily on P retention by soil components. Phosphorus retention by acid soil materials such as Podzols or Spodosols primarily results from P sorption by Al and Fe. To study the retention of P by Podzols eight, sandy pedons in northern Michigan were described and sampled. All eight pedons were well drained and classified as Haplic Podzols (sandy, mixed, frigid Typic Haplorthods). Four pedons were located in a sugar maple (Acer saccharum Marshall) forest, two were located in a formerly cultivated field that has since been planted to red pine (Pinus resinosa L.), and two pedons were located in a formerly cultivated field that had bluegrasses and poverty grass. Al and Fe were extracted with sodium pyrophosphate, ammonium oxalate, and sodium citrate and dithionite. Phosphorus retention was measured using the New Zealand method. Al and Fe contents were greatest in the Bhs and Bs horizons and least in the E horizons. Citrate-dithionite extracted the most Fe from the horizons and pyrophosphate the least. Oxalate tended to extract the most Al and pyrophosphate the least. Most of the Al and Fe was organic bound and crystalline Al and Fe the least. The Ap horizons had more Al plus Fe (1635 mg/kg) than the A horizons (725 mg/kg), indicating some of the Bhs had been incorporated into the Ap horizon by tillage. In A, Ap, E and C horizons oxalate and pyrophosphate extracted similar amounts of Al and Fe. In Bhs and Bs horizons oxalate extracted significantly more Al and Fe than pyrophosphate indicating a significant amount of inorganic amorphous materials was present. In non Bhs or Bs horizons oxalate and pyrophosphate extracted similar amounts of Al and Fe indicating little or no inorganic Al and Fe were present. P retention was greatest in the Bhs and Bs horizons (23.0 %) and least in the E horizons (7.2 %). P retention of A horizons was about one half that of Ap horizons. ODOE values were greatest in Bhs and Bs horizons and least in E and C horizons. Higher linear correlation coefficients were obtained when relating P retention with Al than with Fe extracted by the different extractants from all horizons. P retention was more highly correlated to organic bound Al (r = 0.88) and Fe (r = 0.76) than to non-organic amorphous Al (r = 0.72) and Fe (r = 0.67) determined by the difference between oxalate and pyrophosphate extractable Al and Fe. P retention was more highly correlated to organic bound Al plus Fe (r = 0.91) than to non-organic amorphous Al plus Fe (r = 0.86). P retention was not correlated to crystalline Al (r = 0.00) and Fe (r = -0.02) and negatively correlated to crystalline Al plus Fe (r = -0.51) as determined by the difference between citrate-dithionite and oxalate extactable Al and Fe.

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