Phosphorus adsorption characteristics in forested and managed podzolic soils

Despite the agricultural expansion into Canada's boreal ecoregion, little is known about the phosphorus (P) adsorption capacity in natural and managed Podzols' soil profiles. This information is critical for informing management decisions for P use efficiency and mitigating related environmental risks. Thus, this study aimed to evaluate P adsorption characteristics of podzolic horizons in natural and managed soil using nonlinear Langmuir and Freundlich adsorption models. A batch adsorption experiment was conducted using soils collected from distinct horizons of forested and managed fields in eastern and central Newfoundland, Canada. Nonlinear Langmuir and Freundlich fitted models had r values >.99 regardless of horizons, locations, and management history. The organic LFH, a surface horizon typical for forested Podzols, and a long-term managed Ap horizon had the highest P retention capacities when compared to either newly converted soils or soils used as tree nursery following conversion from natural forest. A significant linear correlation and multiple regression models (p < .05) were established between P adsorption parameters and selected soil properties. Results suggest that following conversion from forest to agricultural use, long-term management that includes tillage and lime and fertilizer application creates an Ap horizon with strong adsorption capacity, which could still fix P and serve as a source of P. The newly converted soils and the deeper soil horizons, for both natural and converted lands, do act mainly as P sinks; hence, crops may need larger quantities of P fertilizer increasing fertilizer expenses and also increasing future legacy P.