How to Measure Soil pH: Methods, Ideal Ranges, and Actions

Expensive fertiliser can go to waste if the soil pH is wrong. pH decides how easily nutrients are available to plants: in soil that is too acidic or too alkaline, some nutrients get locked up and are hard to absorb, even when there is plenty in the soil. That is why knowing the pH is often the first step before deciding a fertiliser dose.

This article covers how to measure soil pH, the pros and cons of each method, the ranges generally wanted, and what to do with the result.

What the pH number means

The pH scale runs from 0 to 14. 7 is neutral, below it is acidic, above it alkaline. The scale is logarithmic: soil at pH 5 is about ten times more acidic than at pH 6. So a one-point difference in pH is a large difference.

Much farmland in Indonesia tends to be acidic, because high rainfall leaches base elements from the soil. Most crops grow well in a slightly acidic to neutral range, around 5.5 to 7, though needs differ between crops.

Methods for measuring soil pH

• Litmus or indicator strips. Cheap and quick. Soil is mixed with water, then the strip colour is compared to a scale. Results are rough and suit a first impression.
• Handheld soil pH meters. Pushed straight into moist soil. Practical, but accuracy varies and they need calibration and care.
• Laboratory tests. The most accurate, usually with analysis of other nutrients and a fertiliser recommendation. They take time and cost per sample.
• Permanently installed soil sensors. Read pH continuously at one point, so changes over time are visible, for example after fertilising or liming.

Taking samples correctly

1. Take several points in one zone and mix them into one composite sample. A single point rarely represents a field.
2. Sample at root-zone depth, not just the surface.
3. Avoid freshly fertilised spots or old piles of organic matter.
4. Separate different zones, such as low and high ground, or blocks with different management history.

What to do with the result

• Soil too acidic: liming, for example with agricultural lime or dolomite, is commonly used to raise pH. The dose should follow a lab-based recommendation, because lime requirement depends on soil type, not just the pH number.
• Soil too alkaline: less common in Indonesia, and the treatment depends on the cause.
• Monitor after treatment. Liming works gradually. Repeated pH readings show whether the change is going as expected.

Why continuous monitoring helps

Soil pH can shift slowly due to certain fertilisers, irrigation water, and leaching by rain. A yearly test gives one snapshot, while an installed sensor shows the direction of change. The trend helps decide when a new lab test and the next liming are truly needed.

pH is also most useful when read alongside other parameters. Moisture, EC, and nutrient content give a complete picture of the soil. The link between pH and nutrient uptake is covered in our soil NPK sensor guide.

Common mistakes when reading soil pH

• Measuring soil that is too dry. Handheld meters and sensors need contact with moist soil. Dry soil gives unstable readings.
• Comparing results from different methods directly. Indicator strips, handheld meters, and laboratories can give slightly different numbers. Compare trends from the same method.
• Measuring right after fertilising. Freshly applied fertiliser can temporarily change readings around the application point.
• Not recording location and time. Without records, later measurements cannot be compared properly.

A permanently installed sensor solves the last two mistakes automatically, since its location and timing are always the same and always recorded.

For many fields, the most practical combination is a lab test as the initial reference, then sensors installed at a few representative points to watch the direction of change. The lab gives trustworthy numbers and a dose recommendation, while sensors tell you when conditions start to shift. This way lab tests are needed less often, yet liming and fertilising decisions still rest on current data.

Frequently asked questions

What is the ideal soil pH?

For many crops, around 5.5 to 7. Some crops prefer more acidic soil, so check what your crop needs.

How accurate are handheld soil pH meters?

Good enough for a field impression if calibrated and maintained. For lime dosing decisions, a lab test is still recommended.

How fast does liming raise pH?

Gradually, over weeks to months, depending on the lime type, how it is applied, and soil conditions.

Monitoring soil pH with InFarmer

InFarmer shows soil pH in real time from the IncludeBox Soil Sensor 7-in-1, which also reads temperature, moisture, EC, and nitrogen, phosphorus, and potassium. pH thresholds can be set per zone, and the history shows the effect of liming over time. The bigger picture of data-driven farming is in our smart agriculture guide.