The main cations we are concerned with for plant growth are Calcium (Ca), Magnesium (Mg), Potassium (K), Sodium (Na). Each plays a role in plant nutrient uptake and plant health. For example, magnesium is one of the key constituents of chlorophyll. Calcium aids in the uptake of all nutrients and helps to build strong cell walls. Calcium and magnesium also play a significant role in the texture of soils. Calcium tends to loosen tight clays; magnesium tends to bind soil particles together.
In order to grow nutrient dense food, our job is to move the ratio of the four major cation nutrients towards balance. The optimum balance has been found to be approximately this:
- Calcium (Ca): 60-70% of CEC
- Magnesium (Mg): 10-20% of CEC
- Potassium (K): 3-5% of CEC
- Sodium (Na): 1-2% of CEC
If your ground is sandy, you will want more Mg and less Ca. If you have clay soil, you will want less Mg and more Ca. If you have achieved equilibrium and your plants are growing very well, the Ca:Mg ratio you actually have is more important than a theoretical ratio. There are actually broad ranges of balanced Ca:Mg ratios. Ca% + Mg% should equal 78% to 82%.
When your soil is mineral-balanced, it’s time to really focus on the biology. Keep your organic matter below 30%; 5% is a nice number where summer is hot; 8 to 9 % is a good number where summers are coolish, such as in the Maritime northwest.
Finally, if your soil is otherwise balanced and you have excess Ca, don’t try to fix it; leave it alone.