Extractability of Manure Phosphorus Applied to Major Ontario Soils Measured By Various Soil Phosphorus Test Methods.

Manure amended soils often contain large amounts of phosphorus (P) soluble in surface runoff and constitute high risk for the deterioration of surface water quality through eutrophication. Typically risk potential for manures P loss after application is represented by amount of manure-amended soil P extractable by various soil P test methods. This study aimed to determine the extractability (i.e., a ratio of the difference between extractable P from P-amended soil and that from zero-P control to total P applied) of manure P after application in Ontario soils. In this study, four types of manures, including liquid swine (LS), liquid dairy (LD), solid beef (SB), and solid poultry (SP), and one inorganic P source (IP) were applied to six major Ontario soils at a rate of 61.5 mg kg^-1 and then incubated for 26 weeks. Extractable P in P-amended soils were determined at 2 days, 2 weeks, 8 weeks, and 26 weeks after application by water extractable P (WEP), Mehlich-3 P, Olsen P, and soil Fe-oxide coated filter paper strip P (FeO-P) methods. Among these four methods, Mehlich-3 and WEP gave the highest and lowest P extractability (41.2% vs. 6.4% ), respectively, for the P amendments, while P extractability measured by Olsen P and FeO-P methods was 25.3% and 26.4%, respectively, across the selected soils and P sources. In the tested soils, the P extractability followed the order of LS≈IP>LD>SB>SP regardless of soil test P methods employed. Among the six selected soils, the Fox sandy loam soil tended to yield the highest P extractability for the tested P sources if the WEP and FeO-P methods were used, while both Mehlich-3 P and Olsen P methods often yielded the highest P extractability in the Brookston clay soil. Our results would be useful to develop the Ontario soil P index.