This is years later that I am reading this thread , but it is sad that Commander Strax hijacked this thread. Insisting that he was right is childish and fanatical. Especially since tons of research contradicts him. Shame on him for his fanaticism. He just shut down the conversation like a bully at best, or to be generous, a big baby.
in any case, I can attest that it does work, and to answer the original question, I use around 100-150 ppm (+the water which is about 180 ppm), but mainly for micronutrients (kelp-based). Since absorption from leaves is around 8x more, foliar sprays should be weaker.