Ask The Expert: The 5S of Soil Sampling
September 24, 2025
October Planning
Graham Gilchrist, PAg - Biological Carbon Canada
You may have heard me say this in the presentations I make about making decisions with good data.
This may be a large assumption on my part, but you may already collect the data on which you base your decisions.
The list might look like this.
My calves at weaning weighed an average of 635 pounds.
I put 10565 tonnes of barley in the bin from the barley fields.
My current liabilities are 50% of EBITDA, down 5% from last year.
I put 105 hours on the combine this fall, using 9,000 litres of diesel.
My hay was 15% protein.
My slaughter steers had 15% of them grade AA or lower.
Since this is a carbon discussion, I want to focus on collecting consistent quality data. It begins with the five S system. The 5S is a methodology used to standardize data collection.
It stands for the following:
Collect your soil samples
The same time of year.
At the same place in the field each year.
At the same 90cm depth.
With the same accuracy.
And send them to the same lab each year.
Why choose this approach? Assessing the same time each year lets you compare identical periods. Collecting data in the fall helps you track soil fertility and soil carbon on a cycle-by-cycle basis. For example, from post-harvest to post-harvest or weaning to weaning for that grass field.
Using the same place (+/- 50cm) for each soil sample meets various protocols that require data to come from consistent locations in the fields. A handheld GPS device is definitely helpful. If using a truck-mounted unit, the GPS antenna should be positioned above the sampling point.
The same 90 cm depth might seem a bit deep if you are use to only taking the top 15cm. The depth covers two issues. You want the full root zone for the soil organic levels (SOC%), and you need enough material to measure the bulk density.
The same level of accuracy is achieved by collecting enough samples to meet a specific error margin. An older Government of Alberta extension document on soil sampling starts their discussion of grid sampling with one sample per acre. That total number of samples (100 for a 100-acre hay crop) involves a cost factor. Several protocols allow recalculations every 5 years. This means you sample the winter field one year, the calving field the next, and so on.
The same lab is included in this list because each lab is not identical. There are variations in how they conduct their tests, and you don’t want the same soil sample to have two different readings because you changed labs.
Graham Gilchrist, PAg
