Soil Sampling Protocol

Template description

A randomized sampling template is a core for the AFRSS method. The template represents a grid with 100 cells resulted from 'modified random sampling' with a distance threshold. The numeration of the sampling cells is selected at random with a careful attention that no points are less than 6 'distance units' (the grid step). Where ever it is not possible to find points more distant than 6 units, the distance threshold is progressively relaxed. This sampling approach prevents the previous sampled cell to get too close to the subsequent ones, failing which would lead to partially redundancy. This occurs for example both for systematic sampling and other sampling plans (Bellhouse, 1977, 1988). Systematic sampling, or other sampling plans that avoid points too close to each other, gives a lower variance than simple random sampling. But the application of the formulae given in the section 'uncertainty' to such sampling plans generally overestimates the variance (Wolter, 1984). 

Spatial dimensions of the template are different depending on the geographical coordinates of the sampling plot, e.g., field. To define the template dimensions one have to select the extreme axis X and Y values. The max axis value (Maxis) defines the size of the template (next Figure). The grid size (Gs) is calculated by dividing Maxis by 10. Following the ISO recommendation (ISO/FDIS 10381-1:2002(E)), the number of sampling points for the composite soil sample is 25. To define the distances between sampling points the Gs has to be split by 5X5 grid. The central sampling point within the grid is found by dividing the Gs by 2 and is assumed to be a position of the soil profile.

Adaptation of the template

For effective implementation of the randomised sampling template, the user has to:

  • Represent the plot/field margins in coordinates of the standard local projection used for topographic or cadastral maps.
  • Define both X and Y Maxis values, as described in previous section and, setup a square accordingly. The coordinates of the corners of this square frame should be preferably "round" figures.
  • Overlay on the square the template with 100 points numbered from 1 to 100, as represented in next Figure.
  • Determine the number 'n' of sampling sites that is conditioned by the plot area and the need to keep the costs to a minimum (Table 1).
  • Select the first 'n' points of the grid if they fall inside the plot. Otherwise select subsequent sampling point (n + 1, n + 2, etc.) until you have 'n' points inside the plot.
Size of Plot Number of composite samples
< 5 ha 3
5 - 10 ha 4
10 - 25 ha 5
> 25 ha 6

Table 1. Recommended number of sampling sites (grids of the template) depending on the plot area.

Sampling location

As follows from the adaptation procedure, the plot/field geographical position, location of the sampling sites and soil profiles are presented in the coordinate system. To keep consistency and possible register of the sampled plots/fields at EU level, the geographical positioning should be fixed in European Coordinate Reference Systems (CRS identifier ERTS89 Ellipsoidal CRS) (Boucher, C., Altamini, Z., 1992). The position should be recorded with the precision of 10m in the field by means of Global Positioning Systems (GPS) to be used for return visits to the sampling site. Data can be downloaded to a portable or office computer for registration and combination with other layers of information for spatial analysis.


  • Bellhouse D.R., 1977, Some optimal designs for sampling in two dimensions, Biometrika 64, pp. 605-611.
  • Bellhouse D.R., 1988, Systematic sampling, Handbook of Statistics, vol. 6, ed. P.R. Krisnaiah, C.R. Rao, North-Holland, Amsterdam, pp. 125-146.
  • Boucher, C., Altamimi, Z., 1992. The EUREF Terrestrial Reference System and its First Realization. Veröffentlichungen der Bayerischen Kommission für die Internationale Erdmessung, Heft 52, München 1992, pp. 205-213.
  • Soil quality - Sampling - Part 1: Guidance on the design of sampling programmes, 2002. ISO/FDIS 10381-1:2002(E).
  • Soil quality - Sampling - Part 4: Guidance on the pprocedure for investigation of natural, near-natural and cultivated sites, 2002. ISO/FDIS 10381-4:2002(E).
  • Wolter K.M., 1984. An investigation of some estimators of variance for systematic sampling. Journal of the American Statistical Association, Vol. 79 No 388, pp. 781-790.

The SOM application allows to execute some examples. The results of the point distribution may be exported either in "HTML Output" or in an "Excel output".

This page aims to present supplementary tools assisting to set up on-line geoposition of the sampling sites and design the strategy to take the composite samples. This work is under progress and the final result will be available after the testing in the field .

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