Coming out of the ground--starting 24 inches below grade with your conduit--you have to protect your wire. You can run conduit for the remaining portion of your run. I wouldn't place it on the ground! If you can run it along side of the deck, then this would be practical. You are going to need a watertight bell box, and a weather proof cover. Make sure you ground your wires to the bell box. This outlet will also have to be GFCI protected [NEC 210.8] If you plan to run conduit for the entire 24'--which I do not recommend, because pulling wire through conduit is not easy--then you can bury your wire in accordance to code specifiactions (requirements). Remember: Once you start to emarge from the ground, you must start your conduit 24" below grade, unless you plan to use RNC, or heavy-wall steel for the full run.
PS: If you plan to use PVC, I would go with Schedule 80
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