There is a simple way to generate dirt if you have mods
the mods that i use to do this are:
1) MineFactory Reloaded
2) Ex Nihilo
3)Ender IO (or any item transporting mods)
First you create a "planter" from MFR, and place it below some dirt, inside you place saplings and set all the filters to saplings
The Planter from MFR: http://i.imgur.com/lQ7ReJe
Then you give it a supply of energy, i use the stirling generator for reasons shown later. i simply place the stirling generator next to the planter.
above the dirt, one block aside, i place the harvester (also from MFR). And i can use "Energy Conduit"s from Ender IO to make the stirling generator below, share energy with it. Note the conduits on the left hand side!
Where to place the harvester http://i.imgur.com/2zx7X9o
The harvester takes trees, when grown, and chops them down, the conduits send the items over to this chest:
The chest http://i.imgur.com/92aaYAI
The chest then, with the help of conduits, takes the saplings and places them in "barrel"s from Ex Nihilo. These compost the saplings and give dirt. On the underside of the barrels i have placed conduits on 'extract' mode, so they extract the dirt and place it in any chest i want