Application of Composted Pulp and Paper Mill Sludge to a Young Pine Plantation

Disposing of sludge recovered from the effluent stream of pulp and paper mills has traditionally involved landfilling. Shortages in landfill space and increasingly stringent environmental regulations in many countries have forced the industry to seek alternative disposal options. We assessed the feasibility of compost-recycling a primary pulp and paper mill sludge (PMS) for use as a nutrient-releasing mulch in plantation forestry. The effects of the composted PMS on the growth, nutrition, water relations, and weed suppression in a 3-yr-old plantation of radiata pine (Pinus radiata D.Don) on an infertile sandy soil in southern Tasmania were assessed. Compost was applied to the surface without incorporation in 0.5-m wide bands in tree rows at rates of 0, 20, 40, and 60 metric t ha -1 (dry matter). One year after application of compost, the percentage increase in stem diameter was 40 to 66% greater than that achieved in untreated plots, with better growth at the highest compost application rate. Improved growth of radiata pine after application of compost was primarily attributable to a 17 to 37% increase in the concentration of foliar N and to decreased water stress in amended plots. Nitrogen released from the compost was mostly absorbed by plant roots within the first 20 cm of the soil profile, with no significant movement beyond this depth range. Application of compost prepared from PMS to young stands of radiata pine was found to be an acceptable recycling alternative for this material, capable of improving plantation productivity.