In the last blog I talked about how we are looking into Conservation Agriculture (CA) and how our soil wouldn’t be easy to convert. Now we are coming to the thorny issue of how to convert, which might take a big leap of faith. Some scientists say that a no tillage system requires the correct balance of calcium and magnesium in the soil and some scientists say this is nonsense.
Those in favour say that this ratio determines gas exchange, or the breathing capacity of your soil. The better a soil can take in oxygen and then release CO2 for photosynthesis the better your production. A soil without breath is like an animal nearing death and the Ca:Mg ratio governs this process.
The reasons given appear complicated. Calcium is a (relatively) large ion with two positive charges. These charges are attracted to the negatively charged particles of clay in the soil. This large ion attaches to clay particles on each side and holds them together as stable soil aggregates with air-space (pores) in between. This process, called flocculation, enables all-important oxygen to diffuse from the atmosphere into the soil.
By contrast, magnesium is much smaller, but also attaches to clay particles on either side with the two positive charges. However, instead of holding the particles together as stable aggregates with pore spaces in between, the much smaller magnesium ions pull them closer together. So, the higher the magnesium in your soil, the tighter it becomes, and the less it can breathe.
They argue that to get soil ready for no tillage you need to achieve the optimum ratio between calcium and magnesium in your soil and this, in turn, depends on the CEC of your soil.
CEC is a measure of the clay component of the soil. A sandy soil might have a CEC of 4, while a heavy clay soil might have a CEC of 40. In the heavy clay soil you need more calcium to help push apart the high clay component. Here, the ideal Ca:Mg ratio might be 7:1. Conversely, in the sandy soil you might need a Ca:Mg ratio of just 3:1, because you need more magnesium to help create structure in a soil where there is none. Therefore, for optimum soil performance you need to get this ratio right.
If they are to be believed then we need to do some magnesium reduction by putting sulphur on the soil. However, some scientists say that this is all nonsense and changing the ratios has no bearing on your soil or yields. It seems that we might have to do some test fields and see how it goes………………..