pH is a measure of the hydrogen ion* concentration of a substance ranging from 1 -14. It is not a measure of the calcium/lime content of a material, or soil in this case!

The lower the pH reading, the higher the hydrogen ion concentration [H+], and the more acidic the soil. The higher the pH, the higher the hydroxyl ion concentration [OH-], and the more alkaline the soil. A soil pH of 6.4 is considered neutral, ie. [H+] = [OH-].

pH is the negative logarithm of the hydrogen ion concentration, therefore if the pH changes by 1, the ion concentration actually changes by 10. For example, pH 5.8 is ten times more acid than pH 6.8, so that a unit change in soil pH is actually quite dramatic!

Hydrogen ions are involved in numerous chemical interactions, so their presence is beneficial, but in large quantities, ie. acidic soils, they start to dominate the soil colloid. Hydrogen is not considered a plant nutrient and its dominance diminishes the potential storage of ‘real’ plant nutrients.

Excess hydrogen also creates highly reactive soils, where miscellaneous chemical reactions become highly probable and compete against plant and microbe requirements. Alkaline soils have no excess hydrogen available, making it difficult for many chemical reactions to occur readily.

Soil pH also appears to have a direct impact on minerals with both low and high pH levels limiting their availability. Interestingly, minerals are all available to some degree at pH 6.4 – and curiously, many systems in nature also work optimally around this pH, includingplant sap and blood.

How do you raise soil pH?

You ‘mop up’ hydrogen ions – no more, no less! There are a variety of ways to do this which can include calcium (lime or Gypsum) – but it is certainly not limited to this.

Lime (CaCO3 – calcium carbonate) mops up hydrogen the following way:

    CaCO3 + 2H+ →  Ca2+ + H2O + CO2

But magnesium carbonate (with no calcium) can be just as effective:

    MgCO3 + 2H+ →  Mg2+ + H2O + CO2

Hydrogen is a highly reactive/aggressive cation capable of stripping other cations from their bonded anionic partners, e.g. (CO3)2-. Calcium, magnesium and other cations are merely passive passengers in the process of raising pH – it is their anionic partners that actually do the ‘mopping up’.

Some unexpected results can occur though. For example, calcium sulphate (CaSO4) found in gypsum can react the following way in the presence of excess hydrogen:

    CaSO4 + 2H+ → Ca2+ + H2SO4 + CO2

H2SO4 is sulphuric acid!! Therefore adding sulphate-based inputs (even with a calcium component) to highly acidic soils can plummet pH levels down even further.

How do you lower soil pH?

Unfortunately it is not easy to add hydrogen ions, or remove excess hydroxyl ions from soil. Nature ‘adds’ hydrogen ions via chemical reactions around the root zone, or removes excesses by leaching materials down the soil profile, but they are generally very slow processes.

Coincidently maybe, but Dr Albrecht noted that US regions of low annual rainfall, hence low leaching potential, such as the central prairies, have alkaline soils, while acidic soils were found in higher rainfall regions on the coastal fringe, such as the redwood forests. He reasoned that the rain flushed the soils toward acidic conditions over the centuries. The same pattern certainly seems to hold true in Canada too!

Humans have tried to speed the process up by incorporating acidic or alkaline materials into the soil – the most radical being the application of straight sulphuric acid to cotton soils in the US (Lost Secrets of the Sacred Ark, p. 172). As you can imagine, the effects on soil health are devastating and the changes to the soil often unpredictable and damaging long-term. But working on changing soil pH alone is often a recipe for disaster…

Why don’t Albrecht advocates focus on soil pH?

Albrecht advocates view low or high soil pH as a symptom rather than a cause. According to Albrecht, all soils have an ideal cation saturation ratio and when this is reached, soil pH automatically corrects itself to 6.4. High or low soil pH is the result of a cation imbalance and correction involves selecting those inputs that help correct the mineral imbalance, not the pH. With this new focus, calcium is obviously not always the answer.

For example:

Problem 1: Soil pH is low. Discover that calcium and magnesium are also both low.

Remedy 1: Add calcium and magnesium based materials to the soil, e.g. gypsum.

 

Problem 2: Soil pH is ideal, but plants are dying. Discover extremely high sodium levels.

Remedy 2: Find cause of high sodium and correct, buffer existing sodium with humates and possibly flush sodium out with irrigation and/orgypsum.

 

Problem 3: Soil pH is high. Discover magnesium is high and calcium is low.

Remedy 3: Strip excess magnesium from the soil using a sulphate, e.g. gypsum, and add plant-available calcium** such as calcium hydroxide or gypsum

#Quantities used are important and should be calculated to prevent further imbalances and disruptions to soil health.

 How do you measure soil pH?

In most cases a solution of soil is tested, with most mobile soil pH kits suggesting a 1 part soil : 1 part water mix. Litmus paper can be used this way, but only indicates whether a solution is acid (red) or alkaline (blue), not the degree of acidity. Water quality can effect the reading due to contamination, so distilled water with a pH of 7 is ideal.

Soil testing laboratories have 2 main methods of testing soil pH

1) pH (water) is the most universally accepted method where soil is mixed into solution with distilled water, as above, though different labs do use different ratios, for example 1:1 or 1:5. If the water is truely neutral, the results should not differ.

2) pH (CaCl2) is claimed to give a more stable soil pH reading***, but the pH readings tend to be much lower than a pH (water) reading.

While there is no clear linear relationship between pH (water) and pH (CaCl2) readings, the following rule of thumb is often used to make conversions.

pH (CaCl2)      pH (water)

  4.5 – 5.8               add 1         For example, pH (CaCl2) of 4.7 = pH (water) of 5.7

   < 4.5                  add 1.5

   > 5.8                  add 0.8

Most laboratories test and report on both pH methods, but there are some laboratories that only test pH (CaCl2), unless specfically requested, and has lead much alarm, with growers thinking their soils had dropped more than a unit within a year!

There is also a wide range of pH meters on the market with varying degrees of accuracy and ease of use.

* An ion is an atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons. Hydrogen atoms that have lost an electron become positively charged ions.

** There are some who claim that magnesium has 1.4 times the effect on soil pH than calcium, and that by feeding the soil calcium and ‘bumping’ off excess magnesium, you can actually lower soil pH.

*** Salts in soils vary from season to season and year to year to give quite different soil pH (water) readings each test. By adding a ‘known’ dilute salt to the soil solution for testing, such as calcium chloride, the variation between pH readings can be calibrated and minimised.

Problem 2: Soil pH is ideal, but plants are dying. Discover extremely high sodium levels. Remedy 2: Find cause of high sodium and correct, buffer existing sodium with humates and possibly flush sodium out with irrigation and/orgypsum.

Problem 3: Soil pH is high. Discover magnesium is high and calcium is low. Remedy 3: Strip excess magnesium from the soil using a sulphate, e.g. gypsum, and add plant-available calcium** such as calcium hydroxide or gypsum #Quantities used are important and should be calculated to prevent further imbalances and disruptions to soil health. How do you measure soil pH? In most cases a solution of soil is tested, with most mobile soil pH kits suggesting a 1 part soil : 1 part water mix. Litmus paper can be used this way, but only indicates whether a solution is acid (red) or alkaline (blue), not the degree of acidity. Water quality can effect the reading due to contamination, so distilled water with a pH of 7 is ideal. Soil testing laboratories have 2 main methods of testing soil pH 1) pH (water) is the most universally accepted method where soil is mixed into solution with distilled water, as above, though different labs do use different ratios, for example 1:1 or 1:5. If the water is truely neutral, the results should not differ. 2) pH (CaCl2) is claimed to give a more stable soil pH reading***, but the pH readings tend to be much lower than a pH (water) reading. While there is no clear linear relationship between pH (water) and pH (CaCl2) readings, the following rule of thumb is often used to make conversions. pH (CaCl2) pH (water) 4.5 – 5.8 add 1 For example, pH (CaCl2) of 4.7 = pH (water) of 5.7 < 4.5 add 1.5 > 5.8 add 0.8 Most laboratories test and report on both pH methods, but there are some laboratories that only test pH (CaCl2), unless specfically requested, and has lead much alarm, with growers thinking their soils had dropped more than a unit within a year! There is also a wide range of pH meters on the market with varying degrees of accuracy and ease of use. * An ion is an atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons. Hydrogen atoms that have lost an electron become positively charged ions. ** There are some who claim that magnesium has 1.4 times the effect on soil pH than calcium, and that by feeding the soil calcium and ‘bumping’ off excess magnesium, you can actually lower soil pH. *** Salts in soils vary from season to season and year to year to give quite different soil pH (water) readings each test. By adding a ‘known’ dilute salt to the soil solution for testing, such as calcium chloride, the variation between pH readings can be calibrated and minimised.