Agrologists say soil sampling is the farmer’s best tool to evaluate the needs of a potential crop.
When to sample
Cultivated fields intended for spring planting should be sampled after Oct. 1 and after soil temperatures drop below 10 C. Ideally, testing would be done in the spring, but isn’t always possible.
Fields for fall-seeded crops should be sampled one month before seeding.
Forage fields for seed, pasture or hay can be sampled any time after Sept. 1.
Frozen or water logged soils should not be sampled because of the difficulty in obtaining a representative sample.
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Where to sample
Each field should be sampled separately. If there have been yield, weed or moisture problems on a field, those patches should be sampled individually.
Avoid sloping land, old fence lines, saline areas, drainage ditches and other odd characteristics not common to most of the field.
Between 15 and 20 sites should provide a representative sample.
Tools
Core sampling tools are best when sampling below 15 centimetres. Augers are also effective, but can mix some surface soil into the deeper samples. Sampling with a spade will work if done carefully, but it is time consuming and not recommended if alternatives are available.
Methods
Clean plastic pails or bags are required. Metal containers can contaminate the samples.
Samples from the same depths may be mixed for an individual field.
Samples should include soil from zero to 15 cm.
For problem areas or fields that may need more selective evaluation of nitrogen levels, samples should be taken from zero to 15 cm, 15 to 30 cm and 30 to 60 cm. These should be kept separate and should come from 15 to 20 sites.
Handling the samples
Mix the sample by hand. Crush any lumps and blend them into the sample. Dry a one-half kilogram portion of the sample on clean plastic sheets. Concrete floors may contaminate samples with lime or other minerals.
The soil should be dried at room temperature without additional heat. Rapid drying will cause variations in nitrogen levels.
Place the dry sample in the plastic sample bag and seal it. Fill out information on the box or label. Ship as soon as possible.
Make a copy of each information label or sheet and file it for future reference. It may be useful in developing a field history.
