It is well known that amendment with organic matter contributes to soil health by e.g. elevating nutrient levels, increasing aggregation, reducing bulk density and increasing the biological activity (Haynes and Naidu, 1998). The different types of organic amendments would be expected to affect soil organic matter levels differently, depending on their quality. It has previously been demonstrated that sludge and manure may have a relatively high stability compared to other sources of organic inputs (Kirchmann et al., 2004). The present observation that already after 4 years the SOM C content was significantly increased in the accelerated compost treatment must mainly be ascribed to a high stability of the compost. The accelerated compost treatment has clearly resulted in an organic matter content distinctly higher than in all the other treatments, but even with the ‘normal’ application rate of compost in which the carbon amendment rate is similar to that in the deep litter and in the accelerated sewage sludge treatment, there is clearly a higher but due to the experimental setup with high input rates, they have occurred within the timeframe of the study.