Soil Sampling Guide
Key things to remember
- Take soil samples prior to sowing.
- Take soil cores only from areas of the paddock with the predominant soil type.
- Store your soil samples is an esky while out in the field.
- On reaching home, store the soil samples in the fridge until you are ready to send them to the lab for analysis.
- Try to send your soil samples to the lab early in the week so that they don’t sit in a post office over the weekend
- Label you soil samples clearly
Soil conditions vary from paddock to paddock and region to region. Each paddock should be considered on a case by case basis. It is essential for Yield Prophet subscribers to source accurate soil test results, as they form the basis of simulations. This page outlines the requirements and processes necessary to acquire accurate soil test results.
To achieve accurate simulations, Yield Prophet needs to know two important things about the soil in your paddock:
- The amount of water and nitrate currently in your soil (determined through an annual soil test)
- The chemical properties of your soil, including any properties that will affect root growth (determined through an annual soil test)
There are three basic steps to obtaining soil test results for Yield Prophet:
- Sampling – taking soil cores from the paddock
- Sample preparation – preparing and packaging soil samples for accurate analysis
- Sample analysis – measuring the amount of water, nitrate and other soil chemical properties.
Sampling for Yield Prophet initial conditions involves taking a number of soil cores from across your YP paddock, splitting them into the depth intervals described below, bulking the separate intervals and preparing and packaging them for analysis.
Soil sampling can be difficult and time-consuming work if you do not have the correct equipment, and accuracy of analysis can be jeopardised by inappropriate sampling methods. Soil sampling contractors (eg. fertiliser companies, resellers, agronomists, farming groups, Departments of Ag) operate in most districts and are an easy, cost-effective alternative to ‘do-it-yourself’.).
It is important that you tell contractors exactly what you are sampling for, as they will often not be used to sampling for soil moisture or at as many depth intervals as required by Yield Prophet. Give them this document to read and, if you or they have any doubts or queries about what is required, or need anything explained, contact Tim McClelland via the details at the end of this page.
If your Yield Prophet paddocks are located in north-west Victoria, BCG can sample, prepare and analyse your soil for use in Yield Prophet. For further details contact the BCG office on 03 5492 2787 or email info@bcg.org.au.
If you are elsewhere in Australia, you or a contractor will need to take and prepare your own samples and send them to a soil lab for analysis. Discuss Yield Prophet soil sampling with your agricultural consultant: you may be able to combine it with regular deep N, phosphorus and moisture testing.
When should I be sampling?
Before sowing! March-April is ideal, so finish reading this page, clarify anything you do not understand and get going! The earlier it’s done, the earlier you will get your results back and the earlier you can log on to Yield Prophet to maximize its use and value.
What soil analysis do I need and how much does it cost?
Yield Prophet models the growth of your crop's roots during the growing season: knowing where the resources (water and nitrogen) are located in the soil profile is essential for accurate simulation of your crop. Therefore, you need to measure initial conditions in at least four different layers down the soil profile eg. 0-10, 10-40, 40-70 and 70-100 cm depth. These are the depth intervals used by BCG. It is not recommended that you use fewer than four layers. You can use more layers if you prefer (eg. 0-10, 10-25, 25-40, 40-55, 55-70, 70-85, 85-100 cm). This will increase model accuracy, but is more expensive to sample and analyse. You should sample down to the maximum potential rooting depth of your crop (which is probably at least 1 m) because Yield Prophet needs to know the total amount of water and nitrogen potentially available to your crop for an accurate simulation.
Soil analysis costs are dependent on the analysis your paddock requires and the soil testing laboratory used. Yield Prophet recommends the use of IPL laboratories. The soil analyses required will depend on whether your paddock has previously been used in Yield Prophet. Tables 1 and 2 below show the analysis required for YP paddocks, the recommended depth intervals and the costs associated with the analysis at IPL,SGS and CSBP Laboratories. These laboratories are suggestions only: all growers are free to use a laboratory of their own choice.
Table 1: Analysis and costs (IPL, SGS or CSBP) for paddocks that HAVE been used in Yield Prophet previously.
| Required analysis | ||||||
| Sample depths | Nitrate & ammonia | Water % | IPL Cost (Inc. GST) * | CSBP cost (Inc. GST) ~ | SGS cost (Inc GST) | |
| 0-10cm0 | | | $32.78 | $22.00 | $16.50 | |
| 10-40cm | | | $32.78 | $22.00 | $16.580 | |
| 40-70cm | | | $32.78 | $22.00 | $16.50 | |
| 70-100cm | | | $32.78 | $22.00 | $16.50 | |
| TOTAL | $131.12 | $88.00 | $66.00 | |||
N.B. *For IPL - Service Fees may apply for data entry and report printing for Non NAA software users - please contact 1800 803 453 for details.
~Discounts avaliable for bulk numbers or when seed samples are also sent in for analysis - contact SGS (mob 0408 037 801) for futher information.
Table 2: Required analysis and costs (IPL, SGS or CSBP) for paddocks that HAVE NOT been used in Yield Prophet previously.
| Required analysis | ||||||||||
| Sample depths | Nitrate & ammonia | Water % | EC* | Chloride | pH (CaCl2) | OC^ | IPL cost (Incl. GST)* | CSBP cost (Incl. GST)~ | SGS cost (Inc GST) | |
| 0-10cm | | | | | | | $45.76 | $42.90 | $35.20 | |
| 10-40cm | |  | | | | | $39.27 | $34.10 | $28.60 | |
| 40-70cm | | | | | | | $39.27 | $34.10 | $28.60 | |
| 70-100cm | | | | | | | $39.27 | $34.10 | $28.60 | |
| TOTAL | $163.57 | $145.20 | $121.00 | |||||||
NB: * EC = Electrical Conductivity, ^ OC = Organic Carbon.
*Fro IPL - Service Fees may apply for data entry and report printing for Non NAA software users - please contact 1800 803 453 for details.
~Discounts avaliable for bulk numbers or when seed samples are also sent in for analysis - contact SGS (mob 0408 037 801) for futher information.
Where in my paddock should I take cores?
For a soil test to provide a reliable guide to the condition of your soil, the sample tested must truly reflect the soil in the area sampled. If the soil type varies, sample the predominant soil type only.
You need to make sure that your soil sample is representative of your Yield Prophet paddock. Ideally, Yield Prophet paddocks should be of a consistent soil type, but all paddocks vary to a certain degree. Ensure that your soil cores are taken from a region of the paddock that is consistent in soil type and covers the greatest area in that paddock. (If you have a paddock with significant variation in soil type, you should consider each soil type as a separate 'paddock' in Yield Prophet and sample them individually). ‘Averaging’ soil types does not work! Select areas to be sampled and take cores at regular intervals as per the examples below, which show where soil samples should be taken in different paddock situations.
Example 1: Paddock with Uniform Soils | Example 2: Paddock with Multiple Soils |
| |  Notes: Two transects in the paddock in the predominant soil type only and avoiding the minor soil type. One Yield Prophet subscription is recommended. |
Example 3: Paddock with Multiple Soils | Example 4: Paddock with Multiple Soils |
 Notes: Ziz-zag pattern in two distinct soil type zones in the paddock. Two Yield Prophet subscriptions are recommended. | |
Other things to consider when taking soil cores are:
- Avoid contaminated and deceptive areas such as in the vicinity of gateways, animal tracks, animal camps, fences, troughs, trees, fertiliser and lime dumps and planter or seeder loading areas.
- Remove surface material such as pasture or weed growth and surface litter in order to bare soil at the sampling site.
- Cropped paddock soil samples cores should be taken from between plants within rows.
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How many cores should I take?
The more cores you take, the more accurate the measurements will be. You need to take at least six cores across a paddock to obtain accurate results. Once cores have been taken, they are usually combined (bulked) according to the depth interval from which they are taken. Lumps should be broken up and soil thoroughly mixed before samples (few hundred grams) are bagged ready to be sent away for analysis.
It is good practice to record where you took your cores from within your paddock (a rough map or description will do) or record the actual points with a GPS if you have one. The Soil Sampling Guide provides a good template for this. This will allow you take soil samples from the same places in future, creating sample consistency from year to year.
How do I prepare my samples?
It is very important that you label your samples CLEARLY with:
- Your name
- Your phone number
- Date the samples were taken
- Paddock name/number
- Depth interval from which the soil came (eg. 10-40 cm)
A permanent (waterproof) Texta on zip-lock bags works well. It may also be advantageous to mark your sample bags prior to going to the paddock. When handling samples, always keep in mind what you are trying to measure in the soil and how that will change as you take it out of the paddock and handle it. Water will begin to evaporate as soon as a core is taken from the ground; work quickly and place the samples into sealed plastic bags (zip-lock bags available from supermarkets are ideal) as soon as possible. Minimise further evaporation and changes in nitrate levels by keeping samples cool: take an Esky out in the field, and store them in the fridge when you get them back home.
If you are posting the samples for analyses (particularly soil water analysis, make sure they are very well sealed in durable plastic bags (again, zip-lock bags are ideal; use a couple). Post them by Express Post to minimise the time in which they can dry out, and post them early in the week so they are not sitting around in a post office over the weekend.
Where do I get my samples analysed?
Growers are free to have their samples analysed at a laboratory of their choosing. Soil analysis costs are dependent on the analysis that your paddock requires and the soil testing laboratory used. YP recommends the use of IPL laboratories. For more information please consult the Soil Analysis Guide which provides:
- Instructions on the analysis required
- Instructions on how to send your samples to the IPL and CSBP laboratories
- A Soil Sampling Record Sheet.
For further information...
Please contact:
Tim McClelland
Yield Prophet Coordinator
p: 03 54 922 787
f: 03 54 922 753
m: 0400 090 659
e: yieldprophet@bcg.org.au