Agri-environmental Thresholds using Mehlich III Soil Phosphorus Saturation Index for Vegetables in Histosols
- Julie Guérin,
- Léon-Étienne Parent * and
- Rahima Abdelhafid
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 (DPSOX) using the acid-oxalate method and setting αm = 0.4, and the water-extractable P (PW) (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 DPSOX than the Bray 1 method (r 2 = 0.62) and the Florida extraction method (r 2 = 0.53). The [P/(Al+γFe)]M-III ratio as index of P saturation (IPSM-III) was the most closely related to DPSOX (r 2 = 0.88) setting γ = 5. The critical [P/(Al+5Fe)]M-III ratio of 0.05 at DPSOX = 0.25 and PW = 9.7 mg P L−1 was validated by an independent study from North Carolina. The soil group (low- vs. high-IPSM-III soils) significantly influenced crop response to added P. Critical agronomic IPSM-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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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