Decomposition of organic matter in forest soils controls mineralization of nutrients. The decomposition is to a large extent controlled by climatic and soil conditions. Four different soil treatments of water and nutrients were applied to a Norway spruce (Picea abies) stand in Denmark, and the relative changes in decomposition rate were quantified by the cotton strip assay. Additions of water and nutrients to the soil increased the decomposition of the cotton strips significantly, especially in the deeper soil layers. Reduced water addition during the summer, thereby creating ‘summer drought’, caused no changes in the decomposition compared to an untreated control situation, but the spatial variability in the decomposition within the treatment plot was strongly increased. The decomposition of the cotton strips decreased linearly with the soil depth (1st order).