title: Approximating Phosphorus Leaching from Agricultural Organic Soils by Soil Testing.
abstract: Phosphorus applied to soils in excess of crop requirement could create situations favorable to P enrichment in subsurface flow that contributes to eutrophication of surface water. This pathway of P loss can be more severe in muck (i.e., organic) soils where agricultural production is intensive. This study evaluated the suitability of various environmental and agronomic soil P tests initially designed for mineral soils to predict dissolved reactive P (DRP) in subsurface flow from organic soils. Intact soil columns were collected from 44 muck soils in Ontario to provide a wide range of soil test P levels. A lysimeter leaching study was conducted by evenly adding water in an amount equivalent to 5 mm of rainfall. The leachate DRP concentration was linearly related to soil water-extractable P and CaCl-extractable P with values of 0.90 and 0.93, respectively, and to Bray-1 P and FeO-impregnated filter paper extractable P in a split-line model with a change point. Mehlich-3 P and Olsen P, a method recommended for agronomic P calibration in Ontario, were not related to leachate DRP concentration. All P sorption index (PSI) based degree of P saturation (DPS) values were closely related to leachate DRP in split-line models, with the DPS indices expressed as Bray-1 P/PSI and FeO-P/PSI having the highest correlation with leachate DRP concentration. Because it is desirable from practical and economic standpoints that the environmental risk assessment shares the same soil test with agronomic P calibration, the two PSI-based DPS indices as presented can be considered as environmental risk indicators of DRP subsurface loss from organic soils.
authors.forename: Z M
authors.initials: ZM
authors.lastname: Zheng
authors.forename: T Q
authors.initials: TQ
authors.lastname: Zhang
authors.forename: C
authors.initials: C
authors.lastname: Kessel
authors.forename: C S
authors.initials: CS
authors.lastname: Tan
authors.forename: I P
authors.initials: IP
authors.lastname: O'Halloran
authors.forename: Y T
authors.initials: YT
authors.lastname: Wang
authors.forename: D
authors.initials: D
authors.lastname: Speranzini
authors.forename: L L
authors.initials: LL
authors.lastname: Van Eerd