Soil sampling

Timing of soil sampling


The purpose of the demonstration trials is to understand the suitability of mixed species cover cropping in southern dry-land cropping systems. We are interested in how cover crops may alter soil fertility and health. This is in addition to better understanding impacts on organic matter and nutrient stratification. This is because we expect cover crops to have most influence on cash crop performance via their impacts on soil properties.

In designing the analytical package for the project, we decided to focus resources on the climatic and soil diversity of the 20 demonstration sites. We did this to best capture the gradient from western SA through to Tasmania. However, a consequence of this is that no temporal data will be collected, thus it is important the sole sampling activity is well timed.

We appreciate that some of the sampling requirements below may appear onerous. However, rigorous sampling is required to ensure that subtle yet important treatment effects are not masked by paddock variability.


We circulated a template spreadsheet early in the project, to be completed for each demo trial site. We require this in order to record paddock management and rotations in the seasons prior to the final cover and cash crops. Whether you have opted for a summer or winter cover crop and subsequent summer or winter cash crop will dictate when soil sampling needs to occur.


In either situation (final winter or final summer crop), the idea is that you will sample soil prior to establishment of the final cash crop. To be clear, this means that you will undertake sampling before any pre-sowing fertilisation or amelioration is conducted, and before sowing commences. More generally, pre-season soil testing is recognised as the most effective way to understand your crop’s nutrition budget. Thus, we wish to align our cutting edge soil health and nutrient flux assays with traditional metrics commonly collected as part of best practice paddock management.

We need growers/collaborators who are managing demo trials to identify likely sampling windows in advance. This will allow the lab to plan logistics, and many of the analyses are time sensitive. We anticipate two sampling windows:

    1. For a final winter cash crop sown in autumn 2021, you should be looking to sample March-April 2021, unless very early season sowing anticipated.
    2. For a final summer cash crop sown in spring/summer 2021, you should be looking to sample September-October 2021.


Sample collection


In order to ensure that samples are easy to identify, CSIRO will supply pre-labelled ziplock bags for sampling. These will be mailed out to the grower/collaborator responsible for sampling each site. They will be labelled according to match site plans provided to CSIRO. Collaborators/growers will be responsible for soil corers for sampling and other paraphernalia (tarps, balances, etc).

Minimum requirements

In order to ensure consistency across the 20 demonstration trials, we have minimum sampling requirements.

  1. At least three cores per plot must be taken, and ideally six. This is to capture spatial heterogeneity and ensure that this does not mask subtle treatment effects.
  2. Each core must be to 1 m depth unless saprolite is reached sooner in shallow soils.
  3. Once all the cores from each plot are recovered, they should be placed side-by-side on a tarp or similar.
  4. All cores should then be divided into 0-10, 10-20, 20-30, 30-60, 60-100 cm segments.
  5. All segments from the same depth should then be combined into one bulk sample in a bucket or similar. This will reflect the soil properties for that depth in that plot.
  6. Pooled segments should then be weighed (a digital airline luggage scale works well hooked onto a pre-weighed bucket) and this weight recorded.
  7. Once the weight of the pooled segment is recorded and the pooled sample thoroughly mixed, a ~150 g sample should be placed in the correct pre-labelled bag. The remainder can be discarded.

Alternative bulk density option

During the November 2019 webinar a couple of advisors suggested an alternative method to quantify bulk density. In some soil types, this may reduce variability in the bulk density numbers generated. However, noting it is also a significant increase in workload, it is optional provided the more basic analysis is completed as above. Cores taken this way must not be used as the samples for biogeochemical analysis above.

  1. Place a drum with the bottom removed over the area to be sampled and press into the soil.
  2. Fill this with water and allow to infiltrate for 24 h.
  3. Push bulk density cores into the soil, taking care not to compress the soil in the process.
  4. Retrieve filled core, extract from corer, place in pre-weighed foil tray and weigh soil on balance with resolution of 0.1 g.
  5. Dry core at 105 C for 48 h.
  6. Re-weigh dry core, subtract tray weight from both wet and dry soil weights.

More information is available here.


Sample shipping

Notifying the laboratory

All samples will need to be sent to the CSIRO Soil Biogeochemistry lab at the Waite Campus in Adelaide. This is a research lab which handles samples from a diverse range of projects. However, given the time-sensitive nature of some of the soil health analyses, it is important that good communication is established. We will need you to keep Dr Mark Farrell (CSIRO project lead) in the loop with planning the timing of your sampling.

Once you have established the likely sampling date, let the lab know when we can expect your samples.

Sample packing and interim storage

For many of the analyses, the first steps need to be undertaken within 48 hours. Thus, it is imperative that samples are shipped expedited to the CSIRO lab.

After sampling, sample bags should be placed in an esky with frozen cooler packs. (Do not use ice as this can melt and contaminate samples). If you cannot make that day’s post, it is preferable to temporarily place the sample bags in a domestic refrigerator. This should only be done if shipping is impossible on the same day. Under no circumstances should the samples be frozen.

You should aim to complete sampling early in a working week so that the risk of the package sitting over the weekend in a warehouse is minimised. The samples are time-sensitive and delays would affect results, likely limiting our ability to observe effects of the cover crop treatments. 

Interstate quarantine regulations

Finally, please note that strict interstate quarantine rules apply in South Australia, which is where the CSIRO lab is based. Because of this, for collaborators sending samples from outside of SA, please ensure you contact Dr Mark Farrell at CSIRO well ahead of time. Doing this will enable preparation of appropriate import paperwork and ensure that samples are received promptly.  This is not a requirement for samples from within South Australia.