Use of Paper-mill Wastes on Agricultural Soils: Is This a Way to Reduce Nitrate Leaching?

The term paper-mill waste is used for different products: de-inked fiber sludge, primary fiber sludge, secondary sludge and mixtures. The aim of this study was to find out if any of these materials can be safely used on agricultural soils to induce net N immobilization of N, and thereby decrease nitrate (NO 3 ) leaching. Chemical characterization showed that secondary sludge derived from biological waste water treatment was a nutrient-rich material low in fiber content, whereas primary and de-inked fiber sludge were high in fiber content and low in nutrient content. Cellulose-C and hemi-cellulose-C amounted to 46% and 36% of the organic C present, respectively, and C/N ratios were around 130 in primary and de-inked fiber sludge. Incubation studies at 8°C over 2 months showed that the decomposability of primary and de-inked fiber sludge in soil was not significantly different. Both showed lower decomposability than secondary sludge. Concentrations of inorganic N in soil declined to very low levels after application of primary and deinked fiber sludge and their capacity for net N immobilization was 4.8-7.2 kg N t - 1 C added at 5°C. However, contents of Cu, Cd and polycyclic aromatic hydrocarbons in de-inked fiber sludge limit its use on arable land. Only primary fiber sludge was found to be suitable as a introgen catch fiber material for use on agricultural soils.