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We investigated relationships between phosphorus (P) availability and fractionation and growth of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) and white spruce (Picea glauca (Moench) Voss) in the Athabasca oil sands region. The study sites had peat – mineral soil mix (PMM) as cover soil over a tailings sand substrate planted to pine or an overburden substrate planted to spruce. Available P was determined using a modified Kelowna extraction and sequentially extracted to obtain exchangeable, Fe- and Al-bound, Ca- and Mg-bound, organic, and residual P. The organic P content in PMM explained 83% and 65% of the variations in available P in the pine and spruce sites, respectively. Phosphorus bound to Fe and Al in PMM was also positively related to available P on pine sites (p < 0.001) but not on spruce sites. Available P in PMM was correlated with aboveground biomass increment of spruce (p < 0.05) and explained 78% of the variation in foliar P. Foliar P in both pine and spruce was lower than the adequate level for tree growth. Low foliar P and available P in PMM affect the successful establishment of pine and spruce trees on the reclaimed sites, and proper P nutrition management is important to overcome P limitation in reclaimed soils.

Applications of sulfate and carbonate salts have been shown to improve the solubility of phosphorus (P) in model calcareous soils. It is unclear how these treatments will influence P solubility in real soils. The objective of this study was to determine the effect of sulfate or carbonate salts on P solubility in selected Manitoba soils. We hypothesized that the application of carbonate or sulfate salts in a fertilizer band could enhance the solubility of P in Manitoba soils. Different salt mixtures were prepared by mixing either monopotassium phosphate (MPP) or monoammonium phosphate (MAP) with K2SO4, (NH4)2SO4, MgSO4, or (NH4)2CO3. After the 2 wk of incubation of salt-treated soils, both P sources decreased soil pH significantly. The addition of salts did not significantly affect pH in most of the soils. There was a significant treatment effect (P < 0.0001), a significant soil effect (P < 0.0001), and a significant soil by treatment interaction (P < 0.0001) on water-extractable P. Coapplication of either sulfates or (NH4)2CO3 salt increased soluble P in some soils by 6%–44% or 11%–14%, respectively. Application of carbonate or sulfate salts increased P solubility only in soils with a smaller ratio of HCl-extractable Ca to ammonium acetate-extractable Ca.

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