Taking a soil test
How do I know when to take a soil test?
The best time to test is when there is some soil moisture, because it’s easier to take the sample however, avoid waterlogged conditions.
Soil testing should be done once a year. It is important to take soil samples at the same time of year, each year, to reduce variability in soil conditions and allow results to be compared from one test to the next.
What tools do I need?
Soil sampling involves taking a number of cores of a consistent size and depth. Specially designed soil samplers which take a 10cm core are preferable to using a shovel. A shovel will take samples at variable depths and collect too much soil per sample.
Soil samplers are commercially available for around $200. An alternative is to contact your local agronomist or reseller who may be able to loan out a soil sampler or even offer a soil sampling service
Follow these tips to ensure your sample will deliver meaningful results:
- Look at the whole paddock and work out what areas to avoid before starting sampling.
- Samples should represent soil conditions in the particular paddock.
- If there are distinct differences within a paddock, there may be different soil types. If different soil types cover significant areas of the paddock you may need to take sets of soil samples. If a different soil type only covers a small area, then just sample the predominant soil type.
- Consider the variations in the paddock determined by soil type, land use, paddock history and animal grazing behaviour before selecting the sample sites.
- Avoid sampling along fence lines, stock camps, under trees, near buildings and troughs, as these areas will have different fertility levels to the rest of the paddock and will give unrepresentative results.
- Avoid sampling from urine and dung patches. These areas are often only obvious when the pasture is actively growing.
Choosing sampling sites
There are two common soil sampling patterns – a zig zag (see Figure 1) and a transect pattern. The most important thing is to make sure the sample taken is representative of the paddock.
Use GPS technology on your mobile phone to record the sampling sites so the same sites can be retested in the future.
How much soil do I need?
Multiple soil cores are essential to produce a representative sample and give a true indication of the soil in a paddock.
Around 20–30 cores are generally required to produce soil tests for most nutrients and soil pH.
More cores may be required for more specific tests such as soil carbon – check with the soil testing lab regarding requirements before sampling.
Once you have collected the required number of cores, mix the samples and place them in a bag labelled with your name, address and the paddock name.