Comparison of agri-environmental phosphorus tests for boreal agricultural and natural Podzols

• Published in: Canadian Journal of Soil Science
• Main Authors: Kedir, Amana Jemal, McKenzie, David Bruce, Ziadi, Noura, Unc, Adrian
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2023
• Subjects: Soil Science; Canada; Bray; Newfoundland
• Online Access: http://dx.doi.org/10.1139/cjss-2022-0037; https://cdnsciencepub.com/doi/full-xml/10.1139/cjss-2022-0037; https://cdnsciencepub.com/doi/pdf/10.1139/cjss-2022-0037

Over a dozen soil phosphorus (P) extraction procedures have been designed for agri-environmental purposes (P-tests). Sustainable expansion of agriculture into boreal regions dominated by Podzols requires further insights into P extractability. We extracted P from Podzol samples ( n = 96) using nine P-tests followed by both colorimetric (P Col ) and inductively coupled plasma (P ICP ) quantifications and assessed the relationships between P-tests. Samples were collected by depth or horizon from agricultural fields and reference sites in eastern, central, and western Newfoundland, Canada. The soil P was extracted with water, citric acid, ammonium bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA), Morgan, Olsen, Bray-1, Bray-2, Mehlich-1, and Mehlich-3 solutions, thus targeting a wide range of extractable P pools in managed and natural Podzols. The soils had a pH of 3.4–6.9, organic matter of 0.5%–47.2%, and Al-M3 of 977–2561 mg kg −1 . On average, water extracted the lowest P Col (1.0) and P ICP (5.7) mg kg −1 , while citric acid extracted the highest P Col (151) and P ICP (290) mg kg −1 . For the managed podzolic soils, the extractability of P followed the sequence water < Morgan < AB-DTPA < Mehlich-1 < Bray-1 < Mehlich-3 ≤ Olsen ≤ Bray-2 < citric acid; this varied slightly by quantification techniques and soil groups. The differences between P ICP and P Col were most significant for the citric acid extracts. Most P-tests measurements were moderately to strongly correlated to P-M3 ICP measurements ( r 2 > 0.50) but variable with quantification techniques and soil depths. Given the diversity in extractable P pools across management-induced soil conditions, it is evident that a fully informed P management for the Newfoundland Podzols will require calibration of P-tests against crop P uptake.