ROLE OF CHEMICAL-CONSTITUENTS OF WHEAT-STRAW AND PIG SLURRY ON THEIR DECOMPOSITION IN SOIL

Carbon mineralization and microbial biomass content of wheat straw (WS ), pig slurry (PS) and their mixture (WSPS), either intact or with ext raction of soluble substances (-SS) or soluble substances plus hemicel lulose (-SSH), added to soil, were monitored over 230 days in a labora tory 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 th e several kinetic models tested to describe the mineralization process , a double exponential model best described the C mineralization of al l the materials, both intact and with extractions. The extraction of t he labile substances from WS, PS and WSPS lowered the values of the ra pidly mineralizable C and of the amount of microbial biomass. The orga nic fraction of WS was found to be almost completely represented by mi neralizable carbon, while PS and WSPS showed only 62% of mineralizable carbon. In spite of this, after 8 months, about half of the initial a mount of the organic C in the intact residues still remained unmineral ized.