Spatial and temporal heterogeneity of soil microorganisms and isoproturon degrading activity in a tilled soil amended with urban waste composts

摘要

Organic wastes addition may impact the pesticide behaviour in soils. Furthermore the incorporation of crop residues or organic amendments by ploughing can induce a heterogeneous spatial distribution of the added organic matter in the tilled layer. Spatial and temporal heterogeneity of soil microorganisms and isoproturon biodegradation was investigated at the decimetric scale in relation to the spatial distribution of organic matter originating from urban waste composts from 1 to 19 months after their incorporation through ploughing. We compared one control plot without compost addition and two plots receiving either municipal solid waste (MSW) compost or green waste co-composted with sewage sludge (SGW) every two years. According to morphological description, the ploughed layer was divided into four zones: the interfurrows, containing important quantities of fresh organic matter, the plough pan and two types of clods, the clods (with no visible structural porosity) and the clods (with visible macropores). Total organic carbon (C) and microbial and fungal biomasses were measured on homogeneous samples taken from each zone. Total C and isoproturon mineralization were monitored for two months at 2 sampling dates. At the end of incubation, samples were extracted to evaluate the nature and availability of isoproturon residues. The results showed that interfurrows constituted a special local environment with the highest level of microbial biomass and the highest isoproturon mineralizing capacities and respiration levels. The presence of compost in the interfurrows stimulated isoproturon biodegradation relative to controls. This effect was more pronounced for the MSW compost than for the SGW compost. Heterogeneity may persist several months after compost or stubble hiding depending on the nature of added organic matter.