Soil pH functions to determine the acidity and alkalinity of soil, and more importantly, serves as an important indicator for soil health, nutrient availability and plant performance. However, what controls soil pH and how can we fix soil pH that is too high or too low? Let’s take a closer look! 

What are some factors which will influence soil pH?

Soil pH is influenced by several factors, which can be categorised into inherent and dynamic factors. Inherent factors refer to natural causes during the soil formation process which determine the natural soil pH, while dynamic factors are man-made actions on soil that changed the pH into what it is today.

Figure 1: Factors Influencing Soil pH

Inherent factors:

1. Parent material: Determines the mineral contents of the soil and whether it is prone to acidification. Soils formed from acidic rocks (e.g. granitic rocks) tend to have lower pH than those formed from basic rocks (e.g. calcareous rocks). 
2. Climate and weathering: Soils in wet and warm climates tend to have more acidic soils, because water will carry organic matter and alkaline nutrient ions away from the topsoil, which are then replaced with acidic H⁺ ions, causing the soil pH to drop. Vice versa, soils in drier and colder regions tend to have more neutral or basic soils due to the lack of water to carry alkaline nutrient ions away. 
3. Texture: Coarser soils such as sandy soils tend to be more acidic due to the lack of small-sized particles and organic matter for nutrient ions to stick onto and be held within the soil. The larger-sized particles also encourage nutrient leaching through runoff. On the contrary, clayey soils with a high amount of organic matter hold on better to the basic nutrient ions and can resist soil acidification. 

Dynamic factors:

The main driving force behind man-made causes of soil pH change is agricultural activities. Below are some practices that lead to soil pH change. 

1. Irrigation: The process of irrigation may induce soil acidification due to the enhanced water flow which results in the leaching of nutrient ions from the soil.
2. Soil additions: Soil additions such as ammonium- or sulphate-based fertilisers used to supply nutrients to crops can lead to soil acidification if used excessively 

What kind of soil does Malaysia have?

Malaysian soil is dominated by the soil types Ultisols and Oxisols (Figure 2), which have an acidic pH range of 4 – 5. Due to a climate which experiences high temperatures and rainfall, these soils are highly weathered and thus have a low pH range. They contain high amounts of aluminium, and lack cations and phosphorus, causing aluminium toxicity and other nutrient deficiencies. Since Malaysian soil is acidic by nature, the soil cannot hold on to nutrient ions easily, hence they tend to leach away, making it unconducive for agricultural activities. This problem is further intensified in hilly regions, as nutrients dissolved in water will tend to flow downhill, causing soils at higher regions to be more acidic than lower regions, affecting durian growers and highland cultivation. Nevertheless, good soil management practices can help make the soil more productive .

Figure 2: Example of an Ultisol (left) and an Oxisol (right) (USDA, 2015).

How can soil pH be fixed to make it more suitable for growing?

Soils which are acidic, such as natural Malaysian soils, can be amended by raising their pH to a range which is suitable for crop production. 

Addition of organic matter

Organic matter in soils usually release nutrients when breaking down and serve as sites of nutrient adsorption and exchange. They act as a buffering agent, resisting drastic pH changes in the soil. Hence, the soil pH will not change easily even when experiencing factors which lead to acidification such as heavy rainfall or excessive fertilization. Organic matter also encourages beneficial soil microbe growth by providing them with a food source, leading to improved soil structure, promoting plant root growth and nutrient absorption. 

Liming 

Lime refers to compounds containing calcium or magnesium which can increase soil pH and lower acidity through neutralizing action. For example, calcium carbonate, magnesium carbonate and calcium oxide. Some are mixtures of liming materials, such as dolomite which is a mixture of calcium carbonate and magnesium carbonate. Lime reacts with water in the soil to produce alkaline anions (e.g. HCO₃^-, OH^-) that react with acidic cations (e.g. H⁺, Al³⁺) and remove them from the soil solution. The soil particles are now free from the acidic ions, and the calcium (Ca²⁺) and magnesium (Mg²⁺) from the liming material can now bind to them instead. In this way, H⁺ ions (causes acidic soil) and Al³⁺ ions (causes nutrient toxicities) are removed, thus helping to increase soil pH and make the soil more neutral. 

Figure 3: Amicote Corbigran

How AgroBridge can help you recover optimum soil pH 

While the inherent climate and soil of Malaysia may cause soil pH to be acidic and initially unsuitable for agricultural purposes, proper soil management practices can help in its recovery. Hence, AgroBridge recommends AMICOTE C-VIDA as a soil conditioner to help you improve your soil pH. 

1. Increases soil pH: A combination of calcium and magnesium compounds helps to remove acidic H⁺ ions, improving nutrient availability and uptake. 
2. Stimulates beneficial microbial activity: The action of beneficial microbes and their metabolites promotes enzymatic activity without oxidising organic matter. 
3. Product in granular form:  Easy and dust-free application process, convenient for usage.

Are you experiencing acidic soil pH? Contact us at +6012-5318161 or directly contact our technical executive in your location for more information and a site visitation today!