MINERALIZATION OF NITROGEN IN A CLAYEY LOAMY SOIL AMENDED WITH ORGANIC WASTES ENRICHED WITH ZN, CU AND CD

This paper deals with the evaluation of the availability of mineral ni trogen in soil amended with different organic wastes (sewage sludges, farm manure, and compost of municipal solid wastes) and the impact of an additional amount of Cu, Zn and Cd on N-mineralization. Net rates o f mineralization fluctuated in the soil amended with organic wastes be tween 11.67 and 33.61 mg kg(-1). The decreasing order of mineralizatio n, expressing a decreasing order of microbiological activity, was: soi l+sludges > soil+manuer > soil+compost > soil. From the kinetic study, it was seen that the mineralization process could be divided into two main periods: the first was from soil moistening up to the fourth wee k and the second from soil 8 to week 16. The first phase of incubation was a period of microbial adaptation to the new environment of soil a mended with organic wastes and enriched with Cu, Zn and Cd. This phase was often marked by N consumption-immobilization. The second phase Ma s characterized by active kinetics of mineralization and intense micro bial activity The influence of the organic amendments according to the value of N-o (the N-mineralization potential) was: N-o(soil) < N-o(co mpost) < N-o(manure) < N-o(sludges). The inhibitory effect of the adde d metals on N-mineralization was: Cd > Cu > Zn. For many reasons, the global effect of metals on N-mineralization was very variable. A suffi ciently long latent time (8 weeks) wits needed for tolerant microorgan isms to release or to start N-mineralization. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.