Soil test results allow farmers to plan annual lime, chemical fertiliser and slurry applications.

Winter is usually the best time of year to analyse soil fertility because restrictions on fertiliser and slurry spreading are in place.

For farms where fertilisers or slurry have been spread right up to the deadline, it is probably best to wait until January to carry out a test, so those applications will be less likely to affect results.

A field should not be sampled for phosphorus until three months after the last application of any fertiliser containing this nutrient.

Test area

When carrying out the test the sampling area should usually not exceed 4ha (10 acres).

The main tool used for sampling is a soil corer. This consists of a steel implement with a handle and a pointed tapered tube at the base which collects samples in a connected container.

The soil core should be pushed to the full (100mm) depth.

At least 20 cores should be taken from the sampling area. The sampling pattern should be carried out in the shape of a W by starting on one arm and following the pattern of the W, finishing on the opposite arm.

When 20 samples are taken, they should be placed in the soil container or bag to make up the sample. The farmer’s name, sample number and field description or plot number should be written on each soil sample bag.

Ensure the sample bag is properly sealed so none of sample spills out of the bags on the way to the laboratory.

The sample log book should be filled out carefully, ensuring that all required details are accurately recorded. Samples should be sent to the lab for testing as soon as possible.

Results

The soil test results usually show the plant-available P and K in milligrams per litre of soil. This result is categorised into a soil index (1 – 4) for each nutrient.

Soils in index 4 are considered very fertile, while soils in index 1 are considered poor. With the results, farmers can develop a fertiliser plan to target areas with slurry, fertilisers or lime that need certain nutrients the most.