AbstractThe shift from conventional to reduced soil tillage may affect physical and chemical soil properties and thereby net N‐mineralization. The aim of this study was to quantify the effect of soil tillage on net N‐mineralization at different depths. For this purpose the mineralization rate in the 0–10, 10–20, and 20–30 cm soil layer of conventionally and reduced tilled, N unfertilized plots under sugar beet was estimated with a field incubation method in 1993 and 1994. This method was compared to a balance method which takes into account N uptake of the crop and mineral N in the soil (0–90 cm).The mineralization rate in 1993 and 1994 was determined by the increase of soil temperature in spring and the change of water content in summer. Although the amount of cumulated mineralized N did not differ. soil tillage affected the mineralization rate in the three soil layers depending on the distribution of organic matter. In the reduced tilled soil the mineralization rate in the upper soil layer (0–10 cm) was higher than in conventionally tilled soil, whereas in the layer 10–20 cm depth the mineralization rate of the conventional treatment exceeded that of the reduced tilled treatment. These differences in mineralization rate between conventional and reduced tillage were more distinct in 1994 than in 1993. Since the amount of N mineralized during the season and the period of highest N‐mineralization rate in the arable soil layer did not differ due to soil tillage the necessity of an increased N‐fertilization in reduced tillage systems cannot be concluded from these results. This is supported by results of the white sugar yield, which showed no interaction between tillage and N fertilization. Results of the field incubation method differed considerably from those of the balance method. This is primarily due to lacking parameters in the N balance.