From an agricultural point of view, a monoculture is dangerous. If everyone grows soy, and something bad happens - an infestation of insects, a mold or some other pathogenic organism - and the soy crop fails, that is a disaster. In an economy as dependent on agriculture as this one, it is a national disaster.
This is reason enough to discourage such reliance on one crop. Now, 36% is not "everyone growing soy" but it's still a level high enough to be potentially dangerous, and that alone would justify, in my opinion, the government acting to discourage it.
