A. J. Kedir, D. B. McKenzie, N. Ziadi and A. Unc, Canadian Journal of Soil Science 2022 Vol. 103 Issue 1 Pages 234-248, https://doi.org/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 (PCol) and inductively coupled plasma (PICP) 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 PCol (1.0) and PICP (5.7) mg kg?1, while citric acid extracted the highest PCol (151) and PICP (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 PICP and PCol were most significant for the citric acid extracts. Most P-tests measurements were moderately to strongly correlated to P-M3ICP measurements (r2 > 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.
