Western Cape Department of Agriculture: Technology, Research and Development: Analytical Laboratory Services: Soil, water and plant tissue lab

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TRD: Institute for Plant Production: Laboratory Services: SOIL, WATER AND PLANT TISSUE LAB

Soil sampling for the small scale farmer or gardener

Soils that are distinctly different as judged by appearance, crop growth, or past treatment, should be sampled separately. Define a sample area based on uniformity of texture, slope, drainage, colour, and past pest and fertility management.
Each sample submitted for testing should be a composite or mixture of separate scattered samplings taken over a well-defined area. Sample areas used for different types of plants separately. For example, keep samples taken from lawn areas separate from samples taken from flower and shrub areas. Areas that are experiencing growth problems should be sampled separately. It is very important that at least five samples within the representative area be taken to obtain the composite sample. More would be better in order to get a more accurate sampling of the area.
Do not sample areas that have been limed or fertilised within the recent past, unless trouble is evident.
Where poor growth exists, separate samples should be taken from both good and bad areas, if possible.
Avoid sampling very wet soils. In soils where fertiliser has been placed in bands (rows), do not sample directly in a band. It is best not to obtain samples very near the edge of the field or plot.
Remove the soil surface vegetation and debris. Using a clean spade, auger, or sampling tube, obtain soil from the surface through the primary rooting zone of the crop using the following practice:
1. Obtain thin vertical slices or cores of soil from the surface to the required depth.
2. If using a trowel or spade, insert the blade into the soil to the specific depth, remove soil and throw it aside.
3. Reinsert the blade to take a thin slice of soil and lift the slice from the ground.
4. Using a knife, cut a 50 mm wide core from the centre of this slice from top to bottom.
5. Place the core (sub-sample) in a clean bucket or other container.
Rooting depth will vary with crop type. For most plants, the top 0 -15 or 20 cm is appropriate. For established grasses, sample the top 0 - 10 cm.
Place each of the randomly spaced samplings in a clean container (bucket, pail or bag) and mix thoroughly. Spread the mixture out on a clean plastic bag to air-dry (do not place soil in an oven).
Mix the soil again. Obtain approximately two to three cups of the soil mixture and place it in a suitable container.
Using a permanent marker, label the outside of the container clearly with your name, telephone number, and a sample reference.

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