Soil Sampling Plan & A Test You Can Trust
Plans composite samples
“The best tip on this tool is probably in the comments already.
Enter your field area and variability to get how many composite samples, total cores and what composite weight to collect — so your soil test rests on a representative sample.
Plan your soil sampling
Next: walk a zig-zag across each uniform zone, mix 10 cores into one bag, and submit 4 composite samples (~2 kg) to the lab.
Sample separate management zones (different soils, slopes, past cropping) independently; avoid field edges, manure piles and wet spots.
Soil sampling — key facts
- Composite samples
- by area × variability
- Total cores
- samples × cores each
- Cores per sample
- ≈ 10–20
- Walk pattern
- zig-zag / W path
- Sampling depth
- ≈ 0–15 cm, uniform
- Composite weight
- ≈ 0.5 kg to lab
- Avoid
- headlands, manure, wet spots
- Privacy
- Runs in your browser; nothing uploaded
A soil test is only as good as the sample
The lab analyses a few grams of soil and you fertilise a whole field on the result — so the sample has to truly represent the field. That means a composite: many cores taken in a zig-zag at one consistent depth, mixed, then sub-sampled, and enough composites to cover the field's variability. Skimp on cores or sample odd spots and the test misleads you, no matter how good the lab.
This tool gives the composite samples, total cores, composite weight and area from your field size and variability. Use it to plan a sampling walk before testing, so your fertiliser, lime and gypsum decisions stand on solid ground. Pair it with the Soil Test Crop Response, Soil Bulk Density, Soil Organic Carbon and Soil Texture tools for full soil management.
Sample representatively
Enough composites and cores for the field.
Walk it right
Zig-zag at one depth, avoid odd spots.
Send the right amount
Know the composite weight the lab needs.
Match the variability
More samples where the field changes.
Frequently Asked Questions
What is a soil sampling plan calculator?+
It works out how to collect a representative soil sample for testing: how many composite samples to take across the field, how many cores go into each one, and the total composite weight to send to the lab. A good plan is the difference between a soil test that reflects the field and one that misleads your fertiliser decisions.
How many soil samples do I need per hectare?+
It depends on field variability. A uniform field may need only one composite sample per few hectares, while a variable field with changing soil, slope or past management may need one per hectare or finer zones. The calculator sets the sample count from your area and the variability you choose.
What is a composite sample and why use one?+
A composite is several individual cores from a sampling area, mixed together, with a sub-sample sent to the lab. It averages out small-scale spot-to-spot variation so one test represents the whole zone rather than a single lucky or unlucky spot. Each composite usually combines 10–20 cores.
How many cores should go into each sample?+
Typically 10–20 cores per composite — enough to average out local variation. Walk the sampling area in a zig-zag and take a core every few paces at the same depth, drop them all in one clean bucket, mix thoroughly, then draw the sub-sample. The calculator multiplies cores per sample by sample count for the total cores to take.
Why walk a zig-zag pattern?+
A zig-zag (or W) path spreads the cores evenly across the sampling area instead of clustering them, so the composite truly represents the zone. Avoid odd spots — old manure heaps, fence lines, wet hollows, headlands and tracks — which would bias the result. Sample each distinct zone or soil type separately.
How deep should I sample?+
For most field crops, sample the plough or root zone — commonly 0–15 cm (about 6 inches) — at a consistent depth for every core, since nutrient levels change with depth. For deeper-rooted or no-till situations you may take separate depth layers. Keep the depth uniform so the cores combine fairly.
How much soil should the final sample weigh?+
Labs usually want roughly half a kilogram of well-mixed, air-dried soil per composite. The calculator returns the total composite weight to collect so you take enough cores to fill that after mixing and sub-sampling, with a little spare. Label each composite clearly with the field or zone it came from.
Does it work for any field size or area unit?+
Yes — enter the area in acres, hectares, bigha, guntha or m², and pick the variability. The tool returns composite samples, total cores, composite weight and the area, so it scales from a kitchen-garden plot to a large multi-zone field.
Are the figures precise?+
They are sound planning figures based on standard sampling guidance. The right intensity depends on how variable your field really is, the crop's value and how precisely you want to manage. Use the plan as a baseline, sample more finely where you know the field changes, and keep depth and pattern consistent.
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