Effect of large manure applications on soil P intensity

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Abstract
The effect of large quantities of manure application on soil P intensity on a Egan silty clay loam (fine-silty, mixed, mesic, Udic Haplustolls) soil from southeastern South Dakota was studied in the laboratory. Soil samples were taken in July 1982 from 0-20 cm depth from plots which received beef cattle manure at the rates of 0, 90, 199, 280 and 361 Mg/ha of manure (dry weight basis) in 1974. soil samples were analyzed for P intensity by the 0.01 M CaCl2 extractable method and for available P by the Bray P1 method. Results revealed that Bray P1 phosphorus increased linearly with manure additions up to 361 Mg/ha. Soil p intensity increased curvilinearly with manure rate and plateaued at approximately 65 .mu.M. The 361 Mg/ha rate did not increase P intensity over the 280 Mg/ha rate. Precipitation of an apatite mineral may have stabilized soil P intensity in this heavily manured soil.