I don't know for sure, but I have some insights based on an experience with an apple tree we had.
The apple tree had received way too much wood ash, and also a bunch of diatomaceous earth. The trunk and branches were splitting in a dry fashion that might be the same fashion your tree is splitting. The leaves were yellow. The tree was probably in desperate need of nitrogen and more acidic soil, and well as some extra magnesium. Wood ash contains lots of calcium and potassium. It may raise the soil PH considerably and potentially hinder nitrogen and magnesium absorption (if used in large amounts).
We had a winter that killed a bunch of cherry trees nearby, I hear. This may also be somewhat responsible for this tree splitting, but our other four apple trees are fine. I suspect the wood ash and/or lack of nitrogen had something to do with it.
I would recommend getting a soil test for PH and nitrogen/potassium/magnesium levels. I suspect giving it more nitrogen and/or Epsom salt (magnesium sulfate) and/or lowering the soil PH may help out. This is just a hypothesis, though. You would need to run tests or experiment to be sure.
Nitrogen does actually help to increase the number of fruits on a plant, I've read, but it doesn't increase fruit size. I believe the benefits of nitrogen are much more pronounced in full sun. Our apple tree gets a lot of sun. Maybe that also contributed to the cracking, but I tend to think it's not the full problem.
If your magnesium levels are fine, but are just being blocked by too much potassium, I recommend not adding too much magnesium to compensate, since once the potassium gets used the extra magnesium might inhibit manganese uptake. I would just add a little extra in this case, and wait out the rest.