Effects of Stockpiling and Organic Matter Addition on Nutrient Bioavailability in Reclamation Soils

Nutrient bioavailability is crucial for vegetation establishment and organic matter cycling after major ecosystem disturbance such as open pit mining. In this study, the stockpiling and organic matter admixing effects on nutrient bioavailability were examined in soils used for reclaiming oil sands disturbed sites in northern Alberta, Canada. Stockpiled and directly salvaged peat mineral soil mix (PMM) and forest floor mineral soil mix (FFMM), the two main oil sands reclamation soils, and a nutrient poor mineral sub-soil (SS) were used in this experiment. Reclamation soils were inter-mixed at different ratios (PMM to FFMM or SS at 60:40, 80:20 and 90:10) to examine the organic matter admixing effects. Significant stockpiling effects on nutrient bioavailability and microbial functions were mostly observed in FFMM. Microbial biomass C was greater, and mineralization of lignin substrate was lower in both stockpiled PMM and FFMM soils compared to the directly salvaged soils. Significant fertility benefit was found in the FFMM-admixed SS and PMM soils through an increase in N and K availability. FFMM admixing also increased microbial functional diversity and assimilation rate compared to the non-admixed soils. Mineralization of polymeric substrates was the main driver of nutrient availability in stockpiled PMM, whereas carboxylic acids and carbohydrates were the major drivers in directly salvaged PMM, as indicated by the Random Forest models. The findings suggest that stockpiling effects are much stronger in FFMM than in PMM, and FFMM admixing to reclamation soils may provide nutritional and microbial functional benefits, especially in nutrient-poor soils.