Not correct I'm afraid bonhe. If for example you give Urea, there will be bacteria which break that down to ammonium. Their numbers will increase in direct proportion to the level of Urea applied. In other words, the microbes are always present and their numbers increase when food for them increases. Adding organic fertilizers will certainly increase decomposing microbes, but the amount of nutrients the plant receives has everything to do with the amount of nutrients applied whether that is from organic or manufactured fertilizer. I think you may be confusing the role of ''beneficial'' microbes. Their high populations are of benefit to plants by being antagonistic to pathogenic microbes (more than their ability to break down nutrients) and for that they are important of course. Consider hydroponics. Organics are almost never used however the plants are very productive. Their root systems team with microbes which no doubt protect them but all the nutrients arrive and are taken up in mineral form. If you believe - as I do - that organics are important because they supply some rare nutrients and more balanced nutrient ratios, then that is another subject.