Initial organic matter transformation of soil amended with composted sewage sludge

An incubation experiment with composted sewage sludge (CSS) just added to t he soil was conducted to determine its initial effects on C decomposition, N nitrification and the transformation of organic matter. CSS was mixed wit h a sandy loam soil from uncultivated ochric epipedon of a Typic Haploxeral f at rates of 0, 40 and 80 t ha(-1) (dry weight). The data obtained showed that with regard to the unamended soil, both the 40 and the 80 t ha(-1) tre atments produced the same result in decreasing respiratory activity, but th e addition of increasing amounts of CSS progressively delayed C decompositi on. The nitrification index (NI), defined as the relation between nitrate-N and nitrate-N + ammonium-N, increased in correlation with the C mineraliza tion coefficient. Total organic matter decreased after incubation whereas t he humic substances increased in relation to the total C mineralized.