Soil Sampling

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 proper tools and documentation.

How Many?

Generally there should be at least one sampler 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 representative 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.

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 three weeks and after tillage to mix the recently applied fertiliser with the soil.

How Deep?

Depth of sampling required depends on how the soil is to be managed. If a 50 cm deep excavation is to take place, then the whole of the 50 cm should be sampled. If the nutrient is to be applied to the surface and left unincorporated, then there is no point in sampling to this depth.

As a simple rule of thumb, you should sample as deeply as the soil you are managing. For arable and cultivated soils this is typically 0-15 cm and is related to cultivation depth. For permanent grassland, a typical depth of 0-7.5 cm is used and is related to the rate of soil formation and animal penetration. 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.).

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