Any analytical result is only as good as the sample taken. A sound sampling strategy will take into consideration the number and depth of samples needed, as well as the proper tools and documentation.
Generally there should be at least one representative sample for each area that is going to be managed. If there is a plan to manage nutrients on a field scale, for example, take one sample per field. If different areas of the field perform in different ways, take a representative sample from each area. If there is a problem area, take one sample from that area and one from the better performing area for comparison. A representative sample should consist of a number of sub samples used to create one bulk sample for analysis.
Samples should be taken before application of fertiliser or treatment. If it is necessary to sample following an application, you should wait a minimum of six months (see RB209 appendix 3 for guidance).
Depth of sampling required depends on how the soil is to be managed.
For arable and cultivated soils this is typically 0-15 cm. For permanent grassland, a typical depth of 0-7.5 cm is used. Deeper sampling may be required for mobile nutrients such as nitrogen, where larger volumes of soil will be disturbed or where soil nutrient problems are identified at particular depths (mineral layers, etc.). Sampling to 30cm depth is required before the establishment of fruit, vines or hops.
What tools are needed?
A soil-sampling auger allows you to sample at depth without digging, making sampling at the correct depth relatively straightforward while also ensuring that the same amount of soil is collected from each sampling location. Use a plastic bucket for collecting cores and mixing them before putting them in the sample packaging. The use of metallic buckets should be avoided as they often contain elements that can contaminate analyses.
Packaging and paperwork
Samples should be packaged securely and labeled individually before shipping. All samples should be accompanied by paperwork that documents the following information:
- Who and where the sample has come from
- Client’s details
- Names of samples (cross-referenced with the samples packaged)
- Details of crops to be grown on the fields sampled
- Soil type
- Expected crop yields
- Whether manure has been applied
- Whether straw has been removed
- Previous lime application – amount, type and date