There are two ways for testing soil pH – the conventional way and the biological way.
The conventional way is a very simple process by simply using an electrical device measuring the pH (normally free of charge). This only measures the amount of hydrogen (H) ions present in the soil and will thus give us only a pH reading.
The biological approach will be to send soil samples to a lab for more in depth testing. For this we use the Albrecht approach and the Australian Perry Agricultural Laboratory based in South Australia.
There is much more in soil pH than just the measuring of hydrogen.
Five elements effect the pH of soil: Hydrogen (H), calcium(Ca), magnesium(Mg), potassium(K), sodium(Na) – the pH will be the sum total of these five minerals. To understand this concept even better it is important to understand that some minerals will effect the pH more than others. For example; potassium (K) will raise the pH 1,7 times more than calcium (Ca) on a 1 to 1 kg basis, magnesium (Mg) will raise the pH 1,4 times more than Calcium (Ca) on a 1 to 1 kg basis.
If we are going to apply only Lime Sand to correct the pH, we can easily over lime, apply too much calcium carbonate and thereby deceive the purpose. The H ion is an acid, non nutritional mineral, responsible for lower pH and Ca, Mg, K and Na are responsible for alkalinity (higher pH). Too much Ca can cause other minerals to get locked up in the soil with devastating effects on plant growth.
Where does H come from?
When a plant is absorbing Ca, Mg, K or any positively charged mineral, it gives a positively charged H ion back to the soil which lowers the soil pH. A soil with 40% H base saturation will be more acidic than a soil with 10% H (the first will have a lower pH than the second). The hydrogen ions are needed in the soil to release minerals from the inorganic, insoluble rock forms to be taken up by the clay-humus particles.
Microbes then work on them to make the minerals available for the crops to be used as nutrition.
When we apply Lime Sand to the soil to supplement calcium to our crops, we know this Lime Sand reacts with the acid-clay of the soil. The acid (H) goes from the clay-humus to the lime rock which, being calcium carbonate (CaCO3), breaks down to form carbonic acid (H2CO3) while the calcium is absorbed by the clay-humus.
Ca attaches to the clay-humus to be available for the microbes and plants. The carbonic acid decomposes into water (H2O) and carbon dioxide (CO2). CO2 escapes from the soil, thereby lowering the acid and neutralising the soil.
Importance of soil balancing: The well known soil scientist Prof. William A. Albrecht dedicated his life on soil pH and soil balancing, proving the importance of using the correct lime source for soil balancing. We don’t want to get rid of all the (H) ions from the soil. What we need is soil fertility in the form of Ca, Mg, K, Na and other bases as plant nutrition. A complete balance of the soil is important.
According to the Albrecht approach we need a percentage base saturation as follows; Ca 60 – 70 %, Mg 10 – 20%, K 2 – 5 %, Na 0.5 – 2 %, H 10 – 12 % and other bases 1 – 10 %. With this percentage base saturation the pH will be near 6,4 which is ideal for both fungi and bacteria. For sandy soils it will be better to see the Ca in the range of 60% and the Mg nearer to 20%. For clay soils the percentage base saturation will be different – Ca closer to 70% and Mg closer to 10%.
With a conventional soil test we may find a soil with pH 8 and think we can’t apply any lime because the pH is already too high. The question to ask is, “Why is the pH 8”? With the biological approach and testing you will find the potassium, sodium or magnesium levels may be too high and there is not enough calcium in the soil.
Some of the soils I was farming on had a pH 8.6 and we never applied any lime on those soils. After gaining a better knowledge and understanding about soil and soil pH, I realised I had extremely high potassium levels with a deficiency of both magnesium and calcium. In dry seasons those paddocks were the first to suffer and when too wet, the weeds would take over. Coach grass and Wild Radish were the dominant weeds and we found it very hard to control them.
After mineralising those soils with a combination of dolomite, lime sand, soft rock phosphate and gypsum it turned out to be the best producing paddocks on the farm. Farmers normally associate fungi with trouble but both fungi and bacteria are playing a very important role in the break down of organic matter and for humus formation. Humus is the key to successful farming. Take the humus out of your soil and the trouble kicks in. Fungi dominates in low pH soils whereas bacteria dominates in alkaline soils but at pH 6,4 both fungi and bacteria are surviving and doing a good job.
The bad fungi’s will dominate in the soil when the percentage base saturation of hydrogen dominates and Ca, Mg, K and Na are on the low end. If plant sap pH is below 5,5 chances are the crops will have trouble with fungi attacks. Spraying a fungicide is not going to fix the real problem therefore you will have to spray it every year. Normally soils lacking in Ca, Mg, S and Cu will have trouble with fungus attacks on the crops. A proper soil test and balancing of the soils according the Albrecht approach will fix these problems permanently, saving you lots of money.
In principle, lime your farm with the aim to correct your soil mineral imbalance rather than just focusing on the soil pH only.
