title: Estimating soil phosphorus requirements and limits from oxalate extract data.
abstract: Excessive fertilizer and manure phosphorus (P) inputs to soils elevates P in soil solution and surface runoff, which can lead to freshwater eutrophication. Runoff P can be related to soil test P and P sorption saturation, but these approaches are restricted to a limited range of soil types or are difficult to determine on a routine basis. The purpose of this study was to determine whether easily measurable soil characteristics were related to the soil phosphorus requirements (P(req), the amount of P sorbed at a particular solution P level). The P(req) was determined for 18 chemically diverse soils from sorption isotherm data (corrected for native sorbed P) and was found to be highly correlated to the sum of oxalate-extractable Al and Fe (R2 > 0.90). Native sorbed P, also determined from oxalate extraction, was subtracted from the P(req) to determine soil phosphorus limits (PL, the amount of P that can be added to soil to reach P(req)). Using this approach, the PL to reach 0.2 mg P L(-1) in solution ranged between -92 and 253 mg P kg(-1). Negative values identified soils with surplus P, while positive values showed soils with P deficiency. The results showed that P, Al, and Fe in oxalate extracts of soils held promise for determining PL to reach up to 10 mg P L(-1) in solution (leading to potential runoff from many soils). The soil oxalate extraction test could be integrated into existing best management practices for improving soil fertility and protecting water quality.
authors.affiliation: University of Kentucky, Soil & Water Biogeochemistry Laboratory, Dep. of Agronomy, N-122 Agricultural Science Building North, Lexington, KY 40546-0091, USA. edangelo@uky.edu
authors.forename: E M
authors.initials: EM
authors.lastname: D'Angelo
authors.forename: M V
authors.initials: MV
authors.lastname: Vandiviere
authors.forename: W O
authors.initials: WO
authors.lastname: Thom
authors.forename: F
authors.initials: F
authors.lastname: Sikora
mesh_terms: D000327:Adsorption; D000383:Agriculture; D005544:Forecasting; D010070:Oxalates / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D012987:Soil; D012989:Soil Pollutants; D014876:Water Pollution / Q000517:prevention & control
chemical_list: D010070:Oxalates; D012987:Soil; D012989:Soil Pollutants; D010758:Phosphorus