Carbon mineralization and microbial biomass content of wheat straw (WS), pig slurry (PS) and their mixture (WSPS), either intact or with extraction of soluble substances (-SS) or soluble substances plus hemicellulose (-SSH), added to soil, were monitored over 230 days in a laboratory incubation experiment. The WSPS showed a CO2 release of up to 23% above that predicted by summing the CO2 evolved from WS and PS. Of the several kinetic models tested to describe the mineralization process, a double exponential model best described the C mineralization of all the materials, both intact and with extractions. The extraction of the labile substances from WS, PS and WSPS lowered the values of the rapidly mineralizable C and of the amount of microbial biomass. The organic fraction of WS was found to be almost completely represented by mineralizable carbon, while PS and WSPS showed only 62% of mineralizable carbon. In spite of this, after 8 months, about half of the initial amount of the organic C in the intact residues still remained unmineralized

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