How to read a soil test without being a technician

You order a soil test, you get a PDF full of acronyms and numbers, you look at it for two minutes and file it in a drawer. It happens to all of us. But a well-read test is one of the cheapest tools to stop fertilising blindly, and the basis of any soil diagnosis.

In this article we explain, line by line, what the most common parameters mean and in what order to look at them, drawing on extension guides from several universities.

Before reading: is the sample good?

The University of Missouri guide puts it bluntly: a test is only as good as the sample sent, and most "odd" results come from inconsistent sampling, not laboratory errors. Its basic recommendations:

• Separate different zones: different soil types, slopes, management or history.
• Take many subsamples in a zigzag within each zone and mix them into a single composite sample. For cropland, the guide mentions 15 to 20 subsamples.
• Always keep the same depth and the same time of year.
• Avoid sampling right after fertilising, liming or applying manure, and when the soil is waterlogged or very dry.
• Label each sample clearly and, if you can, note the coordinates.

If you don't keep the same sampling method, you won't be able to compare one year with another.

1. pH: the first thing to look at

The Missouri guide considers pH the main chemical indicator in the report, because it governs nutrient availability, root growth and microbial activity. That is why it recommends interpreting it before anything else.

• Low pH (acidic): according to the same guide, phosphorus, potassium, calcium, magnesium and molybdenum become less available, and aluminium and manganese can become soluble and damage roots.
• High pH (alkaline): zinc, iron, manganese and sometimes phosphorus become less available.

Montana State University notes that most crops grow best at a pH between 6 and 7.5, and that above 8.3 deficiencies of phosphorus, potassium, iron, zinc and manganese appear. It also warns that lowering the pH of a calcareous soil is very difficult.

What to do: if your pH is out of range, correcting it or adapting management to it is usually the first investment, before adding more nutrients.

2. Organic matter: background fertility

The Missouri guide explains that organic matter stores nutrients such as nitrogen and sulphur and releases them slowly, and that it also improves aggregation, water retention and infiltration. It recommends treating it as a trend indicator: how it evolves matters more than one year's value.

Montana points out that 1% or less indicates a poor capacity to hold water and nutrients. The University of Illinois notes that soils low in organic matter can improve with inputs such as compost.

What to do: if it is low, prioritise practices that build it: cover crops, less tillage, compost or bokashi. And measure again with the same method after a few years.

3. CEC: the soil's pantry

Cation exchange capacity (CEC) indicates how much the soil can hold positively charged nutrients such as potassium, calcium or magnesium. According to Illinois, it depends on organic matter and on the amount and type of clay.

• Montana considers a CEC above 10 meq/100 g adequate.
• Illinois says soils with a CEC of 6 or less need close monitoring for deficiencies such as potassium.

Montana adds that CEC is very hard to change, but that increasing organic matter can improve soils limited by a low CEC.

4. Phosphorus, potassium and other nutrients

This is where most money is spent, and where most can be saved. The key is the rating that usually accompanies the number (very low, low, medium, high, very high). The Missouri guide explains that when the level is high or very high, the probability that the crop will respond to more fertiliser is low in the short term. Montana sums it up with the idea of a "critical level": above it, adding that nutrient will probably not increase yield.

Watch out for an important detail Missouri highlights: if the laboratory's extraction method changes, don't compare raw numbers between tests; compare the ratings.

5. Salinity and sodium

If the report includes electrical conductivity (EC) or sodium, look at them. Montana considers a soil saline with an EC above 4 mmhos/cm, with water stress and nutrient imbalances for the crop. Missouri explains that excess sodium can disperse clays and cause crusting, poorer infiltration and waterlogging.

A simple order for reading it

1. Is the sample good?
2. pH.
3. Organic matter and CEC.
4. Ratings for phosphorus, potassium and other nutrients.
5. Salinity and sodium, if present.
6. Comparison with previous tests done the same way.

What the test doesn't tell you

A chemical test does not measure soil structure, infiltration or the life within it well. That is why it is worth complementing it with field observation, bioindicator plants and simple infiltration or earthworm tests. And if you want to prove your farm's improvement to third parties, the test is the basis of the regenerative passport.

Illinois recommends repeating tests every three to six years to see trends; Missouri speaks of two to three years in many systems. Choose a rhythm and stick to it.

From paper to decisions

A well-read test tells you what you don't need to buy and where it is worth investing. If you want us to review your farm's tests and turn them into a management plan, write to us.

Be the one who does it.

Sources

• University of Missouri Extension (2026). Understanding Your Soil Test Report (G9077). https://extension.missouri.edu/publications/g9077
• Montana State University Extension (2025). Soil Test Interpretation. https://landresources.montana.edu/soilfertility/soilscoop/ss_InterpSoilTest.html
• University of Illinois Extension. Interpreting Test Results. https://extension.illinois.edu/soil/interpreting-test-results