Analytical Methods:Point Counting

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[edit] Point Counting

Standard micromorphological description is a qualitative or at best semi-quantitative technique. The frequency of soil components are estimated by reference to standard guides as a percentage of surface area. However, this approach is open to bias and is sensitive to issues such as the magnification chosen. To provide the quantitative data required for statistical comparison of different sections and soils a range of quantitative methods have been devised. Image analysis systems have been used but require specialist image capture hardware and analytical software. Another approach is point counting.

At its simplest point counting consists of a grid of squares laid over the slide and the feature lying directly below each intersection is recorded. Once all intersections have been recorded the number of points at which particular features (voids, organic matter, charcoal etc.) are summed to produce relative frequency data (e.g. Davidson et al. 2004). The choice of the size of grid and the level of magnification are crucial to the success of this technique. they should be based on the size and frequency of the features of interest and the need to analyse sufficient numbers of datapoints to make the results statistically valid. Other approaches have included dividing the slide into squares and estimating the frequency of different soil components within each square, thus analysing the whole slide whilst obtaining an estimate of variability (e.g. Chrystall, 1997).


[edit] References

  • Chrystall, F. (1997) Soil Micromorphology and spatial interpretation of Mediaeval agricultural landscapes. Unpublished, PhD thesis, University of Stirling.
  • Davidson, D.A. , Bruneau, P.M.C., Grieve, I.C., and Wilson, C.A. (2004) Micromorphological assessment of the effect of liming on faunal excrement in an upland grassland soil. Applied Soil Ecology, 26, 169-177.


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