How representatively can we sample soil mineral nitrogen?

Spatial distribution of soil mineral-N content (Nmin) is a scalevariant process. Precision farming assumes knowledge about the spatial distribution of Nmin. Moreover, sampling in management zones is based on the assumption of spatial dependence between sampling points. In the present study, variability structure of Nmin and the sources of variability were investigated. Within an agricultural landscape, Nmin 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 0–60cm can be expected. Uncertainty due to analytical errors were in the order of 5–10 kg N ha–1 for a 0–60cm layer.