Environmental phosphorus risk classes for silage corn in the Fraser Valley, Canada

• Published in: Agriculture, ecosystems & environment ecosystems & environment, 2025-04, Vol.381, Article 109423
• Main Authors: Nyamaizi, Sylvia, Messiga, Aimé J., Cade-Menun, Barbara, Cornelis, Jean-Thomas, Smukler, Sean M.
• Format: Article
• Language: English
• Subjects: Critical P saturation index; Optimum silage corn yield; P loss; Water-extractable P
• ISSN: 0167-8809
• DOI: 10.1016/j.agee.2024.109423

High soil phosphorus (P) concentrations accelerate P losses from intensively managed farmlands and must be reduced to mitigate eutrophication and water quality concerns, without reducing crop yields. Using 140 soil samples from silage corn fields within the Fraser Valley, British Columbia, Canada, water-extractable P (Pw) was positively related to the P saturation index (PSI) by linear regression (R2 = 0.89). We established critical values for PSI 10.8 % and Pw 4.1 mg kg–1 for P loss risks and identified four environmental risk classes. Soils in the low risk class (PSI = 0–6.6 %, Pw = 0–2.2 mg kg–1), had the lowest Mehlich 3-P (PM3) concentrations, but yield was 13.7 Mg ha–1, below the optimum provincial range (20–25 Mg ha–1). In the moderate risk class (PSI = 6.6–10.8 %, Pw = 2.2–4.1 mg kg–1), soil P was sufficient to achieve optimum silage corn yield (22.2 Mg ha–1). Conversely, in the high (PSI = 10.8–24.3 %; Pw = 4.1–10.3 mg kg–1) and very high (PSI > 24.3 % and Pw > 10.3 mg kg–1) risk classes, soils had excessive P concentrations (PM3 > 200 mg kg–1), but corn yield did not increase. Soil P must be reduced in the high and very high risk classes to reduce runoff loss risk, which will not affect crop yields. Our study shows that P fertilization could improve yields in the low risk class, but must be done carefully to minimize the likelihood of P loss risks. •Degree of P saturation (DPS) correlates strongly with water-extractable P (Pw) and P saturation index (PSI).•Critical DPS of 25 % was associated with values of PSI 10.8 % and Pw 4.1 mg kg–1.•Using PSI, four environmental P risk classes were identified - low, moderate, high, and very high.•For moderate risk class, P inputs must match the level of crop removal.•Fields in high/very high risk classes had excessive STP but no yield increase; fertilization must be reduced.