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The effect of biowaste compost application on the organic matter status of sandy agricultural fields was studied on two long-term experimental sites in Lower Saxony. The organic carbon, the microbial biomass (SIR), the basal respiration, the metabolic quotient (qCO2) and the Cmik/Corg ratio where chosen as indicators for the organic matter status of the soil. Soil sampling was carried out one year after the last compost application. The proportion of added organic matter remaining in the soils was higher at high application rates than at low ones. Organic carbon content only increased clearly if more than 20 t DM ha -1 year -1 were applied. The supply of easily decomposable organic matter by compost and the decreased soil acidity enhanced the soil microbial activity measured as basal respiration, while the microbial biomass showed a less intense increase. Therefore, qCO2 was higher if compost was applied. Neither the Cmik/Corg ratio nor the basal respiration related to the organic carbon (basal respiration kg-1 Corg) indicated an increasing availability of SOM. [ABSTRACT FROM AUTHOR]