I talked to a friend yesterday on a road trip, so we hade a long discussion about riza, he has a degree in agriculture. This is what I came away with out of our discussion. Bottom line is, if your tree is alive, it is already inoculated with riza. A tree cannot live without it. The roots cannot take in water or nutrients on it's own without riza. My advice would be when you repot and your tree that has a good colony of the stuff, leave a couple of long roots alone when you trim the rest of the roots and just coil the long roots back under the trimmed roots, if you are worried about riza. Obsessing over tree care can cause a lot of stress to you and the more you screw with your tree, the more stress you cause it. There is NO ONE WAY to maintain bonsai. Some are going to live and some are going to die, good luck and I have an Indian potion that will cure everthing from toenail fungus to bad breath and grow hair for only $19.95 a bottle, call BR 549, shipping included.
Harry