Lots of variables here: what sort of guidance do you have? terrain? how close can you hold the position of the N? How much N are you putting down? All of it? what sort of residue for a JD single disk planter coulter?

One advantage to 20" rows is that there are more ft of row per acre, 50% more, so the fertilizer density near each plant is not as great - but still enough to burn if you are right over it.

Ideally if you had autosteer and could maintain about 4" from the fertilizer to the seed that would probably work nicely if you can get through the residue with the coulter. With liquid you should also try to get the slot at least covered with soil.

On a planter the JD single disk fertilizer coulter works well and losses are not an issue because the row cleaner and planter row unit tires almost always follow directly behind the JD coulter covering the fertilizer.  running on a separate bar you could lose a lot of N if the weather does not cooperate and you leave an open vee down to the liquid. Depends on conditions. 

Best of luck. Jim at Dawn