Soil Balancing, Part 3 (Calcium and Magnesium)

October 30, 2023

Calcium and magnesium are two of the major minerals and should collectively fill about 80% of the soil’s base saturation in a soil with a 7 pH or lower.

Calcium is needed the most – more than any other mineral (by both weight and volume) and is the major growth mineral that contributes to both the strength and quality of the crops being grown. It’s also important for good soil structure and breathability, which is essential for water retention, microbial activity, and the carbon and nitrogen cycle. Calcium desired value is 68% of base saturation, with a minimum of 1000 ppm or 2000 pounds per acre, whichever measurement your soil report is using.

Magnesium gives structure to the soil. Magnesium desired value is 12% of base saturation, with a minimum of 100 ppm or 200 pounds per acre.

The calcium to magnesium levels and ratio set the stage for the rest of the nutrients and biology. If the calcium is too high in relationship to magnesium, the soil tends to be looser but can lose its structure because it doesn’t have enough “glue” to keep its structure. On the other hand, too much magnesium makes the soil tighter and sticky. When it rains, a lot of the mud will stick to your boots.

This is important information – the general rule of the thumb is to increase the desired percentage of calcium on hard clay soil so that the water and air can enter easier, or increase the desired value of magnesium on light sandy soil to keep the nutrients and water from just leaching away.

It is also important to clarify that, so far, we have talked about the base saturation of calcium and magnesium. The base saturation calcium, what is in the soil profile, is not the same as available calcium content, which is available to the actual crop.

When you take a soil test and get a report back, it is important, even critical, to understand which is being tested. The best scenario is when both are tested and both sets of numbers are used to determine the best recommendation for going forward.

When plants are grown with adequate levels of available calcium, they are much more robust and stockier, with short internodes, resulting in plants that can both set and fill more fruit without collapsing in the process.

Deficiency of available calcium leads to:

  • Poor growth energy – especially quality growth.
  • Poor root development – no white hair roots.
  • Less uptake of other minerals – calcium is a major trucker of minerals into the plant.
  • Minimal immune response to diseases and insects.
  • Foliar applications with minimal results.
  • Plants in the fruit fill stage experience a rapid downward spiral of plant and root health.
  • Many other challenges.

The challenge is that available calcium is not generally understood. Just because you add calcium to the soil does not guarantee that the available calcium number goes up. Instead, when conditions are not optimized, the calcium accumulates in the soil, pushes out other nutrients, and increases the soil pH.

Available calcium can be increased by applying boron, sulfur, silica, and increasing humus content. Humus seems to be an important element in keeping the calcium available on a continual basis.

You can also apply gypsum, which is calcium sulfate and does not build the base saturation calcium content. My preference, actually, is to apply gypsum (or other appropriate calcium source for your situation) with lots of boron and elemental sulfur. The combination of these drives results.

I also speak to excess base saturation calcium, which is hard to remediate. Usually, it takes a lot of elemental sulfur to achieve that – in clay soil with high calcium and 8.0 pH, it can take as much as 2600 pounds of sulfur, something that you don’t want to apply all at once.

Alright, I’ll leave you with some final thoughts:

Complete soil considerations need to include these three: the physical properties of the soil, the biological, and the chemical. The chemical balance is the balance of all the nutrients that are discussed.

The physical, biological, and chemical components all have an impact on each other. For example, the type of soil (physical), and the balance of calcium and magnesium (chemical), seriously impact the biological because of oxygen/gas exchange.

Oxygen is key to paramagnetism. If you want strong and healthy roots, increase the paramagnetic effect in your soil. Paramagnetic force is to roots what light is to photosynthesis. Light is absolutely essential to photosynthesis, which means that paramagnetic force / oxygen is absolutely essential to roots.

And to increase oxygen/gas exchange in your soil, you need to correct the calcium to magnesium ratio.


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Source: Melvin Fisher | Sponsored by Keystone Bio-Ag LLC