The voltage between the ground and any point in the atmosphere is rather high (about 100V/meter). If one suddenly shorts this down to the ground with a pole like you describe, the electrons will rush up fron the ground through the conductor to the air. While this current is initially flowing, the intensity might be quite high, but the equilibrium will be reached within a tiny fraction of a second. The total energy involved would be rather small.

Then, if you keep things like that, the top of the pole will remain almost at the same potential as the ground, but there will still be a tiny difference. Because of air movements, 'fresh' air will replace the ionized air, and some more electrons will keep flowing up on a regular basis... But this current will be very small, over a small voltage. Therefore, the power will remain tiny. Probably too small to be transported anywhere without being completely lost. This is assuming that the pole's outside surface remains perfectly isolating. That is, never gathers any dirt, any moisture, and is perfectly pure in the first place... Otherwise, this tiny continuous current will also flow along the outside surface of the pole, and that would ruin the whole thing...

Maybe this would work once we invent the ultra-isolating pole with a high-temperature-pure-superconducting core, as well as other superconducting wires to get this power where it's useful, all this built with technologies cheap and clean enough to justify the hassle... which I doubt, given the tiny power one can expect to extract from a single such pole.

I'm pretty sure that with the same land surface, much more electricity can be produced by growing crop and burning it... Admittedly, there's much less poetry in this solution, though.