The ideal size of a sample is contested, but an average of c.50
liters is preferable. No less that 20 liters should be taken if possible.
Why is such a large volume of soil needed?
DENSITY - the density of plant material in samples varies. This can be due to the original quantity deposited, the conditions of preservation, or the degree of disturbance.
PRESERVATION - even if a sample is rich in seeds, the preservation may not be good. To identify grains and seeds to species, from which the greatest amount of information can be gained, the surface (cellular) pattern is required. The poorer the preservation, the greater the difficulty of seeing this structure.
A large sample increases the potential of retrieving sufficient numbers of identifiable seeds, and therefore producing a valid interpretation.
What happens next?
Once the soil sample is taken, it is double bagged, with a label placed inside and outside. This records the site code, date, context and sample no., or locus and pail no. (this depends on the excavation style - both pinpoint the sample to its location on the site). Examples are shown below.