Soil Sampling Protocol
|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:
|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.
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.
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 .