Earth-mode is interesting. https://sites.google.com/site/sub9khz/earthmode with frequency being so low and the power needed it might not be practical. Those people seems to have tried to use utilities as antennas. The French around WWI apparently had some ground telegraph developed and produced about 10k units of it.
From the blog link:
> Foremost in sub-9kHz through the ground communications was John, G0AKN, who sadly is a silent key.
From the blog link:
> Foremost in sub-9kHz through the ground communications was John, G0AKN, who sadly is a silent key.
That's an endearing way of putting it. I like it.