Effects of de-inking paper sludges on soil properties and crop yields

The paper mills in Quebec produce approximately 330 000 Mg of raw de-inking paper sludges (RDS) per year. These residues are rich in cellulose and lignin and may be used as soil conditioner. The effects of RDS on soil chemical properties, barley (Hordeum vulgare L. 'Chapais') growth, nutrient uptake and yields, and their residual effect on a subsequent strawberry (Fragaria × ananassa Duch. 'Kent') crop were investigated on a Tilly silt loam (Gleyed Humo-Ferric Podzol) from 1994 to 1996. Four rates of RDS (0, 15, 30 and 45 Mg ha −1 ) on a wet-weight basis were combined with four rates of supplemental N-mineral fertilizer (0, 45, 90 and 135 kg ha −1 ) as NH 4 NO 3 The soluble inorganic N content of soil sampled 30 d after treatment application was significantly lower in plots treated with 45 Mg RDS ha −1 at all N rates. However, soluble inorganic N concentrations increased significantly with RDS rate to 20-cm depth in June 1995. The RDS application increased soil water content and Mehlich-3-extractable P, K, and Ca in the first year. Barley yields were reduced by 50% when 45 Mg RDS ha −1 was applied without supplemental N-mineral fertilizer. The amount of N-mineral fertilizer needed to overcome N immobilization resulting from RDS increased with RDS rates. Strawberry yields were not significantly affected by residual RDS or N-mineral fertilizer. Changes in plant tissue metal contents were not significant. The results of this study indicate that RDS application has a positive short-term effect on soil water, P and K availability but reduces plant-available soil N in the growing season after spring application. The RDS may be used effectively as soil amendment if the crop receives adequate supplemental N-mineral fertilizer. Key words: De-inking paper sludge, N immobilization, barley, strawberry