Soil Sampling Procedure
The following soil sampling procedure was written in collaboration with the Upper Brumby Catchment Group. All of the steps will be applicable to all situations, except Step 3 which may vary depending on the circumstances.
Ask whether the lab you are using is accredited for the tests that you want done. The lab should have National Association of Testing Authorities Australia (NATA) and/or Australasian Soil and Plant Analysis Council Inc. (ASPAC) accreditation.
The results you get from year to year will be more consistent and comparable if you use the same lab each time.
There are a number of different sampling patterns that can be used to give reliable results for soil testing, including sampling a zig zag pattern across a paddock, walking a circle around a paddock, or randomly sampling a small area which is typical of the paddock. To return to the same place each time, establish defined transects across every paddock, and mark them using GPS and by painting fence posts. This transect line can be followed whenever the paddock is sampled.
No matter what method you use to collect your soil samples, it is important to avoid small atypical areas in the paddock, including changes in soil type, breaks in slope, fence lines, waterlogged patches and obvious stock camps. If the paddock is made up of large areas with different characteristics then these areas should be sampled separately. If using the transect method, some paddocks with two distinct soil types will require a transect line for each soil type. These will be tested separately. If they produce the same results the two transects can be sampled separately and the samples mixed together, giving one sample for the paddock.
Make sure you sample at the same time every year, preferably when you can be sure that the soil moisture will be the same, as differences in soil moisture can affect the results. The preferred time is usually spring or late winter.
Sample to the same depth every time the paddock is sampled (150 mm is standard for cropping, and should be used even during pasture rotations; 75 mm is standard for pasture). It's difficult to compare results from samples that have been taken from different depths.
The soil samples should be taken using a tube sampler, or spade. If an auger is used, care must be taken to avoid sample mixing.
For a standard paddock (approximately 20 ha) at least 50 individual cores should be collected. These should be mixed to form the sample for the paddock. As paddock size increases, so should the number of cores (e.g. for an 80 ha paddock you should collect at least 100 cores).
The cores should be spread out evenly along the transect (i.e. take 25 from the first half of the paddock and 25 from the second, spread out along the transect). Avoid taking samples from where there are dung or urine patches, or from where plant growth appears unusually good or poor.
The cores should be collected into a clean bucket (with no trace of fertilisers in it), mixed well and put into a clean plastic bag.
Make sure all samples are labelled clearly (some labs will supply labels for you).
Keep the samples cool (use an eski to store them in) and send to the lab ASAP.
If you have a GPS (and plenty of time!) you may wish to record the location that individual cores are taken from, and collect from this location whenever you sample.