Résumé

Soil organic matter amendments, originating from waste materials, could be used to enhance soil organic carbon 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 composition and their impact on soil organic carbon (SOC) storage. Accordingly, the long-term effects of different organic matter (OM) amendments on the amount and composition of particulate and mineral associated soil organic matter (SOM) were investigated. To examine amendment impacts, surface soils were sampled from a long-term field experiment under cropping rotation, which received 0.4 kg organic carbon (OC) per m2 of urban compost or cattle manure (FYM) addition biannually since 1998. The composts were produced from home sorted organic wastes mixed with green waste (BIO), residual municipal solid waste after separate collection of packaging (MSW) or a mixture of green waste and sewage sludge (GWS). SOM pools were separated by a combined density and particle size fractionation and analyzed for C and N contents as well as C composition by solid-state 13C NMR spectroscopy.

Farmyard manure and urban waste composts from BIO and GWS resulted in increased SOC and N stocks in bulk soils, occluded particulate organic matter <20µm (oPOMsmall) and clay fractions. The high variability of the composition with each amendment type   was reflected in the POM fractions but not in the highly uniform composition of the mineral-associated OM. We suggest that the OM composition in the clay fraction is determined by the microbial residues that are independent in their composition from the input material. Soil wettability was not affected by the amendments and all soils remained hydrophilic even after long-term amendment. Application of BIO and GWS enhanced OC and N stocks in bulk soils and especially the fine mineral fraction in a magnitude similar to conventional FYM.

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