Well Alchemy is a mixture of science and magic, and I believe Nick mentioned this in book one. You have to look into the molecular structure of the object to transform it and that's how Nick made trees from the wooden floor of the dojo. He returned them to its original for like he did to the Lotan.
I agree with SC. Earth Magic does compliment Nicholas' alchemical abilities very well since his craft deals a lot with science - biology and chemistry - which is essentially the root of Earth Magic or as Tsagaglalal says of all the Magics.