Like ICanHazCookie suggested, set up some Sludge Boilers from MFR.
Set up a couple working MFR Harvesters (wheat farms, tree farms, whatever), provide them power (EU or MJ), then set up a liquid pipe to dump the sludge they produce into powered Sludge Boilers - the sludge boilers will create a ton of materials - Dirt, Clay, Sand, Mycellium, Cracked Sand, and Quicksand (maybe even Soul Sand I can't remember). I've have a extra-dimensional barrel filling up with Cracked Sand and I don't even have the biome for it enabled in my config. Just make sure you're ready for the influx of materials; I suggest at least a Deep Storage Unit for all the clay you'll get, it's a little insane...
Keep in mind though, the Sludge Boilers will poison you while they're working if you're nearby. Keep them tucked back somewhere underground.