Project Code: ROCKY-01-009
Sponsor:Rocky Wood Preservers Ltd.

This study explores the development and use of composted sawmill wood residues. The study involved a literature review on compost use in silviculture, a wood waste composting pilot study, development of a compost operations manual, greenhouse and field trials using composted wood waste, and a cost/benefit analysis.

The literature review focused on physical, chemical and biological modifications of soils as they relate specifically to potential forestry operations such as reclamation of degraded sites, transportation of bulk materials, use of wood residuals, and collaboration with municipal waste management programs. Compost application has shown to improve or ameliorate water retention, compaction, soil structure, nutrient deficiency, extreme pH, ion exchange, mycorrhizal association and disease infection. The benefits of compost application are not universal, and therefore careful consideration must be made prior to the application of compost.

Composting hog fuel and post peelings is a relatively easy process given that the recommendations detailed in the compost operations manual are followed. The Carbon/Nitrogen (C/N) ratio of the final product remained high (100+). Normally, organic materials with C/N ratios above 30 cause N immobilization when applied to soil, resulting in N deficiency for plants. However, the C/N ratio could be lowered with the addition of mineral N during the composting process.

Survival and growth of coniferous seedlings following soil amendment with wood-based compost was evaluated in the greenhouse and in degraded and non-degraded field sites. The potential for development of disease suppressive compost from conifer bark was also evaluated in a laboratory bioassay. Wood-based compost and/or fertilizer was found to significantly improve white spruce seedling survival on the degraded field sites. However, when not combined with a fertilizer application, wood compost was associated with reduced growth of lodgepole pine and white spruce in the greenhouse, likely a result of N immobilization in the compost. The compost prepared from conifer bark was found to suppress the damping-off by Rhizoctonia solani in all cases.

Composting wood residuals using a windrow system as detailed by the compost operations manual, is estimated to cost $10-20/tonne. The current market price for bulk, non-specialized compost in southern Alberta is about $20/tonne (loaded at the composting site). In cost/benefit analysis, Rocky Wood Preservers found that the cost of producing compost exceeded the current market price.