Soil phosphorus dynamics in a long-term field experiment at Askov |
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| Authors: | G H Rubaek E Sibbesen |
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| Institution: | (1) Department of Soil Science, The Danish Institute of Plant and Soil Science, Research Centre Foulum, P.O. Box 23, DK-8830 Tjele, Denmark |
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| Abstract: | Inorganic and organic soil P (Pi, Po) fractions were followed monthly for 15 months in a 100-year-old, fertilization and crop-rotation experiment with the Rubaek-Sibbesen, macroporous resin method, the Olsen method, and the Hedley fractionation method. Resin P, and Olsen P had similar levels and variation patterns. They increased in spring after fertilization, decreased during summer and autumn, and increased again in winter after repeated slurry applications. Resin Po decreased in spring and peaked in summer. The variation in time of the Hedley Pi and Po fractions was relatively smaller and was neither related to season nor to fertilization. Unmanured soil contained much less total P than NPK and slurry-treated soils, but the differences in total Pi were greater than those in total Po. Neither total Pi nor total Po concentrations differed between NPK and slurry treatments, indicating that Po in animal manure is quickly mineralized. All Pi and Po fractions were smaller in unmanured than in fertilized treatments. These differences were relatively largest for resin Pi and resin Po, i.e., the most labile fractions, and decreased for the medium and less labile Pi and Po fractions. The reactions by resin Pi, Olsen P, and resin Po to seasons and treatments indicate that these fractions are estimates of the most labile pools of Pi and Po in soil, which make them relevant for shortterm studies. The medium and less labile Pi and Po fractions of the Hedley fractionation method seem more relevant for long-term studies. |
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| Keywords: | Total soil phosphorus Fractions of organic and inorganic soil phosphorus Resin extraction Seasonal variation Long-term fertilization |
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