There are growing interests to use co-composted drilling wastes contaminated with
hydrocarbons as growth media for planting in land reclamation. However, such use of the compost may have potential problems such as inherent toxicity of residual
hydrocarbon and microbial N immobilization due to high compost C to N ratios. We investigated the growth, biomass production, N uptake, and foliar delta13C of white spruce (Picea glauca [Moench] Voss) seedlings in a pot experiment using 1-, 2-, 3-, and 4-yr-old composts (with different
hydrocarbon concentrations and C to N ratios) and a local noncontaminated soil with (200 kg N ha(-1)) or without N fertilization. Growth and N content of seedlings (particularly N content in roots) were lower when grown in the compost media as compared with those grown in the soil. Within the compost treatments seedling growth was affected by compost age, but the magnitude of growth reduction was not linearly proportional to
hydrocarbon concentrations. Plant N uptake increased with compost age, which corresponds with an increase in indigenous
mineral N concentration. Effects of N fertilization on N uptake were curtailed by the presence of indigenous
mineral N (e.g., in the 4-yr-old compost) and by fertilization-induced stimulation of microbial activities (e.g., in the 1-yr-old compost). The differences in foliar delta13C values between seedlings grown in compost and soil (P < 0.05) suggest that limitations on water uptake caused by the residual
hydrocarbon might have been the predominant factor limiting seedling growth in the compost media. This study suggests that
water stress caused by residual
hydrocarbons may be a critical factor for the successful use of co-composted drilling wastes as a growth medium.