Sewage sludge is increasingly used as a fertilizer because land application is considered a more environmentally friendly disposal method and because of its great fertilizer value (Table 3.3). Nowadays, sewage sludge can be produced for agricultural use as dry granular, palletized, or fortified organic-based materials, which have more specialized uses in agriculture and horticulture compared with the conventional forms . The technology for applying sludge is advanced and includes surface spreading and injection of the material into the soil, a practice that helps reduce odor problems and facilitates proper incorporation into the soil. The optimum dose of application is difficult to determine because of restrictions that depend on soil parameters, such as pH, clay content, and contaminant and nutrient content in sludge . Usually, if no other restricting factors are present, the rate of application should not exceed 10 t ha-1 yr-1, equivalent to 250 kg N ha-1 .
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