Title: Phosphorus Availability in Biosolids-Amended Soils.

Quantifying labile phosphorus (P) pools in biosolids is needed to manage biosolids for both agronomic and environmental purposes. Phosphorus indices originated in an effort to protect surface water quality from-non-point-agricultural P inputs. The objectives of this research were to: (1) evaluate soil test components of the western Oregon P index in field and laboratory experiments; (2) evaluate soil test methods for assessing labile P; (3) determine the relative availability of fertilizer and biosolids P; and (4) evaluate the P sorption index [PSI; defined as the molar ratio of P/(Al+Fe) * 100 as determined by acid ammonium oxalate extraction] as an indicator of water-soluble p in biosolids and as an indicator of labile P in soil following biosolids application. Soil samples were collected from 18 western Oregon field sites with a history of biosolids application and analyzed for labile P via oxalate extraction (P0), anion exchange resin (AER) extraction, Bray 1 Redacted for privacy extraction, and dilute salt extraction (0.01 M CaC12). In comparison to untreated buffer areas, biosolids application at field sites increased mean P0,, AER-P, Bray P