A series of laboratory and field investigations were performed to investigate the effect of cereal straw incorporation on microbially mediated processes in a range of soils from North Eastern Scotland. The incorporation of cereal straw residues, at two field sites, caused the microbial biomass to increase in magnitude. Similar results were found in laboratory studies. Repeated incorporation of cereal straw caused an increase in the fungal component of the microbial biomass. This resulted in an altered pattern of decompositon for subsequently added carbonaceous substrates. The productuion and accumualtion of acetic acid in aerobic soil systems was monitored in laboratory incubations. It was proposed that the accumulation of acetic acid was found to be controlled by redox potentials at the sites of microbiological activity. Straw was not observed to increase acetic acid production. Fertiliser nitrogen had both a stimulatory effect on acetic acid production (by stimulating decomposition, and oxygen consumption), and an inhibitory effect (added nitrate buffering a fall in redox potential). Gaseous nitrogen loss via denitrification and ammonia volatilisation was monitored at two field sites. These nitrogen losses were found to be low. Straw incorporation did not increase the magnitude of these losses and under certain circumstances, reduced it.