A sample of soil taken from the field will contain mineral particles of very different sizes. There may be sizeable stones in it which have to be removed in order to obtain a homogeneous sample on which to conduct soil investigations. This is unfortunate because the field behaviour of a soil may be markedly affected by the presence of stones or large gravel. Some aspects of soil science, particularly those concerned with cultivation, require to be investigated on samples whose condition is as little removed as possible from that existing in the field. Chemical and similar analysis, which can only deal with small quantities of material, require sieved samples to ensure uniformity and for this purpose soil passing the 2 mm. sieve is the standard.
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