title: Soil testing to predict phosphorus leaching.
abstract: Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water-soluble phosphorus (WSP), 0.01 M CaCl2 P (CaCl2-P), iron-strip phosphorus (FeO-P), and Mehlich-1 and Mehlich-3 extractable P, Al, and Fe. The Mehlich-3 P saturation ratio (M3-PSR) was calculated as the molar ratio of Mehlich-3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl2-P, and FeO-P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich-1 P, Mehlich-3 P, and the M3-PSR), although the M3-PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich-3 P and M3-PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.
authors.affiliation: Department of Plant and Soil Sci., Univ. of Delaware, Newark, DE 1917-1303, USA. rmaguire@udel.edu
authors.forename: Rory O
authors.initials: RO
authors.lastname: Maguire
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Sims
mesh_terms: D000383:Agriculture; D005544:Forecasting; D008962:Models, Theoretical; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry; D018570:Risk Assessment; D012989:Soil Pollutants / Q000032:analysis*; D014881:Water Supply
chemical_list: D012989:Soil Pollutants; D010758:Phosphorus