title: Agri-environmental thresholds using Mehlich III soil phosphorus saturation index for vegetables in histosols.
abstract: The P concentration in Norton Creek which drains cultivated Histosols in Quebec showed median concentration exceeding up to 14 times the environmental guideline of 0.03 mg total P L(-1). The aim of this study was to develop environmental and agronomic thresholds using soil tests to provide a tool for P management in Histosols. Soil samples were collected from Histosols across Quebec (82) and in fertilizer trials (66) to calibrate soil test methods against the degree of P saturation (DPS(OX)) using the acid-oxalate method and setting alpha(m) = 0.4, and the water-extractable P (P(W)) (Sissingh, 1971). The field trials on crop response to added P were conducted with carrots (8), potatoes (11), onions (10), Chinese cabbage (7), celery (10), and lettuce (20). Relative yields were computed as yield in control without P divided by highest yield with added P. The Mehlich III (M-III) P extraction was more closely related (r(2) = 0.73) to DPS(OX) than the Bray 1 method (r(2) = 0.62) and the Florida extraction method (r(2) = 0.53). The [P/(Al+gammaFe)](M-III) ratio as index of P saturation (IPS(M-III)) was the most closely related to DPS(OX) (r(2) = 0.88) setting gamma = 5. The critical [P/(Al+5Fe)](M-III) ratio of 0.05 at DPS(OX) = 0.25 and P(W) = 9.7 mg P L(-1) was validated by an independent study from North Carolina. The soil group (low- vs. high-IPS(M-III) soils) significantly influenced crop response to added P. Critical agronomic IPS(M-III) values were found between 0.10 and 0.15. Those environmental and agronomic benchmarks are instrumental for managing the P in vegetable-grown Histosols.
authors.affiliation: Department of Soils and Agri-Food Engineering, Université Laval, Québec, QC, Canada G1K 7P4.
authors.forename: Julie
authors.initials: J
authors.lastname: Guérin
authors.forename: Léon-Etienne
authors.initials: LE
authors.lastname: Parent
authors.forename: Rahima
authors.initials: R
authors.lastname: Abdelhafid
mesh_terms: D000383:Agriculture / Q000592:standards*; D002138:Calibration; D004784:Environmental Monitoring / Q000592:standards*; D005308:Fertilizers / Q000706:statistics & numerical data; D008956:Models, Chemical; D010758:Phosphorus / Q000032:analysis*; D011792:Quebec; D012987:Soil / Q000032:analysis*; D014675:Vegetables / Q000254:growth & development; D014877:Water Pollution, Chemical / Q000517:prevention & control
chemical_list: D005308:Fertilizers; D012987:Soil; D010758:Phosphorus