Soil samples can be taken at any time of the year, although spring and fall sampling are usually the most convenient. Separate samples should be collected from areas that differ in soil texture, soil color, the kinds of plants previously grown, and previous applications of fertilizer, organic amendments, and lime. Samples are most easily collected using a soil tube, soil auger, or a garden trowel or spade. Soil samples can be taken with either disturbed or undisturbed stratification. The former are those which are taken without maintaining the natural structure. Undisturbed samples are removed from the earth carefully using a cutting cylinder so that the structure is retained. The size of a soil sample depends on the test procedure to be used and is generally between 0.3 and 1 kg.