EFFECT OF LARGE MANURE APPLICATIONS ON SOIL P-INTENSITY

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 pM. 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. © 1990, Taylor & Francis Group, LLC. All rights reserved.