How to increase the pH of your soil


When looking at a hand full of soil, it might not look very active, but your soil is a container for a dynamic system of biotic (living) and abiotic (physical) processes.

This means the composition of your soil is constantly changing and to ensure good yields, farmers must adjust to keep the soil composition at an optimal level for the best yields.

In our previous article on the pH of soil and how you can decrease high pH levels, we mentioned that the pH of your soil has a significant effect on plant health, as it affects nutrient availability and biological processes in plants.

In this article we discuss the factors to keep in mind when you want to neutralise acidic soil, or increase the pH levels of your soil.

Acidic soil decreases the solubility of important nutrients, and this means your fertiliser becomes inefficient as the plants are unable to absorb sufficient amounts of nutrients to fulfil their needs, ultimately leading to low yields.

On the other hand, low pH levels cause increased solubility of aluminium (Al) and manganese (Mn), which can be toxic to plants. Low pH levels also affect microbial activity in the soil, which is also needed to release certain unavailable nutrients in the soil to plants.

There are several reasons why the pH level dips below a level of 6 or 7.

Plant material, in general, is alkaline and by removing plant material through harvesting or other farming practices, the soil becomes more acidic over time. This is one of the main human-induced reasons for the acidification of soil.

If nitrogen is inefficiently applied in the soil, increased amounts of nitrates are produced. If the nitrate levels surpass the needs of the plant, and the surplus amount is not incorporated into the nitrogen cycle of plants, nitrate leaching will occur that will also lead to acidification. Causes for increased nitrate levels are fertiliser use, especially ammonium based fertiliser, as well as legume fixation.

High rainfall can lead to leaching, which also leads to acidification.

Organic matter that decomposes produces carbonic acid, and high levels of decomposition can lead to increased levels of acid.


The first step when adjusting the pH level of your soil is, as always, to perform a soil test to determine the exact pH level so you can prepare the correct amount of substance you want to adjust your soils with.

  • Do not lime your soil if you are unsure of the pH level as it can lead to alkalinisation.
  • The optimal method to increase the pH levels of your soil is by means of liming. The amount of lime required depends on the soil pH profile, lime quality, soil type, farming system and rainfall.
  • There are several lime options available to help you to neutralise your soil.
  • This includes lime sand, crushed limestone and dolomitic limestone that consist of calcium carbonate and magnesium carbonate.
  • When dissolved, the calcium and magnesium will neutralise the acidity of the soil.
  • The main factors that affect the efficiency of a specific lime is its neutralising value and particle size.
  • The neutralising value of lime is expressed as a percentage of pure calcium carbonate which is given as a value of 100%.
  • If this number is high, you need less lime to obtain your preferred pH level and vice versa.
  • A smaller particle size means the time to neutralise your soil will be quicker.
  • Over-liming, however, can also lead to an increased pH level above the optimal, which will also lead to a decrease in nutrient availability.

It is also worth noting that it takes a lot of time for the lime to react with the soil so you should plan liming well ahead of the planting season, and repeat treatments might be necessary.

Wood ash (potash) is an alternative that can be used instead of lime. It also contains other beneficial nutrients, like potassium, for your plants. Potash is very soluble, so if the potash from your fire got wet in some way, it might not be efficient anymore.

Keep in mind that the composition of wood ash varies from sample to sample, especially if you use wood ash from your own fire.

Also read:
Do it yourself: Making your own basic soil pH test
How to lower the pH of your soil



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