Influence of Limed Sludge on Soil Organic Matter and Soil Physical Properties

Abstract

Some of the methods used for sewage sludge treatment may greatly influence the agronomic properties of the resulting product. One of these is liming which is employed to stabilize and flocculate sludge. With the high rates of lime actualy used in the treatment plants (10 to 50% of the dry matter (1), it is obvious that sludge quality should be widely modify. Beyond an important dilution of the sludge components (1), liming leads to the loss of nitrogen by NH₃ volatilisation (2), and when applied on crop land limed sludges produce a reduction not irreversible, however, of the soil phosphate mobility (3–4). Among the positive effects it should be reminded that liming is followed by the reduction of 98 to 100% of the pathogenic germs present in the sludge (5), and that no detrimental effects on cultivated plants were observed after limed sludge applications even at high loading rates but increasing of production yields were obtained (6–7). In addition to this two essentiel aspects of limed sludge agronomic properties will be developped in this paper: its organic value and especially its role on some soil physical characteristics. Some of the results reported here after have been already published concerning limed sludge organic matter behaviour in soil (8), and sludge consequences on soil structure and water retention (9). All were obtained from the experiments described below.