Urban waste composts enhance OC and N stocks after long-term amendment but do not alter organic matter composition

Organic matter (OM) amendments, originating from waste materials, could be used to enhance soil organic carbon (SOC) storage and fertility of cropland soils. However, there is a limited understanding about the long-term effect of different urban waste compost amendments on soil organic matter (SOM) formation processes and their impact on SOC storage. Accordingly, the long-term effects of different OM amendments on the amount and composition of particulate and mineral associated SOM were investigated. Surface soils were sampled from a Luvisol under cropping rotation, which received biannually 0.4 kg organic carbon m 2 in form of three different urban composts or cattle manure for a period of 15 years. Despite similar C input, different urban waste compost amendments resulted in contrasting C storage. While there were no C stock changes for municipal solid waste compost amended soils, composts from organic waste and green waste and sewage sludge increased SOC stocks in a similar range as conventional farmyard manure. In bulk soils, SOC stocks were increased by approximately 30%, in occluded particulate OM