Use and environmental implications of pulp-mill sludge as an organic fertilizer

Pulp-mill sludge is an industrial by-product with a high level of organic matter, which is eventually biodegradable. Since there are few alternatives for its practical use, its utilization as an agricultural fertilizer is proposed. An experiment was carried out during 2 years, with yellow lupin plants (Lupinus luteus L.), in order to define the critical application levels of this material. Biodegradability of the sludge in the soil was also evaluated, as well as its pollutant effects. Results obtained in the first year of the experiment showed that an application rate larger than 50 t ha(-1) of pulp-mill sludge, has a depressive effect on yield. Yet, this effect is completely dissipated in the second year. Finally, it is concluded that, if the use of this organic waste as an agricultural fertilizer is adequately monitored, soil pollution problems should not occur.