Why is soil pH an important characteristic to measure? Soil pH influences nutrient availability and toxicity. It also influences microbial activity. Soils with pH less than 7 are called acidic and those with pH greater than 7 are called alkaline,
protocol by Steve Vanek
Brief Materials:
- pH meter, calibrated with buffers at pH 4 and 7.
- Air dried or moist soil, 2mm sieved is best.
- Distilled water (very low dissolved solids drinking water will work, e.g. Dasani, battery water) sometimes rainwater caught in a clean container, but this should also be tested by measuring with both types of water, distilled and the substitute, and seeing if there is a difference.
- Small plastic cup
Brief procedure:
- Weigh out 10 g of dry soil into the cup. If the soil was not previously sieved, Remove small stones and larger roots as you weigh.
- Add 20 mL distilled or other verified water
- Stir or swirl cup for 1 minute, you can use a small spoon to stir or break up clods.
- Let sit 2 min.
- While holding the pH meter sensor in the liquid above the soil, move the meter gently to equilibrate it with the liquid and note how the reading is changing.
- When the reading has stopped changing or changes only very slowly (for example, less than 0.1 pH unit in 30 seconds) you can note the reading to the nearest 0.1 pH unit, for example 4.9. Differences more precise than this are not important.
- Below is approximate ranges of pH that affect crops. Adding organic matter to soils may help to ameliorate the effect of low pH even if the pH does not increase by much.
Below 4.5: VERY ACIDIC, many crops affected
4.5 to 5.5: MODERATELY ACIDIC, sensitive crops affected while most crops tolerate, though some negative impact. Aluminum starts going into solution in this range.
5.5 to 7.5, IDEAL RANGE for most crops and varieties. Potatoes may have increased scab incidence and some other diseases are also promoted.
Above 7.5, Alkaline soils, may correlate to salinity problems for crops in a dry climate soil
pH materials
