Soil incubation experiments were carried out under field conditions during a wheat growing season from fallow to crop period to analyze N-NO, production and its spatial variability. Two plots having two different cultivation predecessors (com: plot AM and soybean: plot AS) were sampled in each case along a transect. The semivariogram technique was used to study spatial variability. Coefficients of variation of the N-NO, production were between 40 and 120%, and in so instance was spatial dependence observed in the mineralization process. All the variance could thus be related to short range effects (less than 10 m). A comparative analysis was possible as no spatial structure was found in neither of the plots. Plot AS mineralized 15% more than plot AM, during the whole experiment, this differences could be located along the sowing-tillering stage. Net mineralization rate was 4.5 times greater for plot AM than for plot AS. Possible causes of the observed differences as well as the influence of spatial variability on the number of samples needed to detect effects of interest are discussed.