How representatively can we sample soil mineral nitrogen?

Spatial distribution of soil mineral-N content (N_min) is a scale-variant process. Precision farming assumes knowledge about the spatial distribution of N_min. Moreover, sampling in management zones is based on the assumption of spatial dependence between sampling points. In the present study, variability structure of N_min and the sources of variability were investigated. Within an agricultural landscape, N_min was investigated across a field in a nested design over four consecutive years. Temporally unstable structure of individual nests require a sampling with several nests in the field. In the investigated field, 35%-49% of the total variability derived from small-scale variability observed at spatial distances of <5 m and from sampling and analytical errors. Differences between 10 and 26 kg N ha^-1 for the soil depth increment 0-60 cm can be expected. Uncertainty due to analytical errors were in the order of 5-10 kg N ha ^-1 for a 0-60 cm layer.