I planted the persimmon tree last November which was about 4 years old. The tree seemed to be ok until July this year. Then, I recently noticed that a majority of the leaves on the tree have been turning brown on the edges and many are curled. I am a novice tree grower and don't know what to do for this tree. Can anybody give me any advice?
Whilst these trees can suffer various leaf problems, to be honest, this one looks like its suffering from drought. If the tree was four years old when you planted it, and its only been in a year, and especially if you live somewhere which has hot and dry summers, it would have needed a minimum of a couple of gallons of water every 4 or 5 days or 4/5 gallons every week or so, throughout any hot and dry period. This is true of all new plantings of trees and shrubs, in particular during their first two years. I know you have an irrigation system, but I doubt that would have provided enough water for this tree. I suggest you leave a hose trickling at the base for an hour or two, or carry cans and water thoroughly with about 6 cans full now. Then make sure you keep it well supplied with water until late autumn (or fall, depending where you are).
Could be too much water, but seems unlikely unless for some reason drainage is poor in that area. If you're not sure, I'd be inclined to dig down and reveal the soil around the rootball, or the rootball itself, preferably without breaking roots, just to see whether its dry or wet or whatever...
Of course, if it is too wet, some nutrients may be washing out of the soil so the plant's going short, and it might mean you've got a Leaf Blight, which is prevalent in wet conditions, but it doesn't exactly look like Leaf Blight so much, though I can't see up close of course. Link below talks about Leaf Blight
This link is actually Australian, but might be useful for diagnostic purposes
I'm curious as to what the heap behind the plant in the picture might be...
Now I've read your description of how you planted the tree, it may well be suffering from too much water. It's never a good idea to dig a hole, fill it with good compost or good soil and plant, especially if the surrounding soil is solid clay or otherwise poor. What you've made is the equivalent of a sink, where all the water drains to because it can penetrate more easily where you have planted. The best way to plant in those circumstances is to dig over an area at least 6 feet by 6 feet, incorporating composted manure or whatever, let that settle for a week or so, then dig your hole and plant your tree.
As for staking, yes, a tree does need staking, particularly against a prevailing wind to prevent it leaning over, but not so that it cannot move at all - the movement of air through the leaves and branches and main trunk, causing slight movement of the mainstem (but not the rootball), cause the trunk to thicken up and become stronger - without any movement at all, the trunk is in danger of remaining thin and weak. If you're interested in this, look up thigmomorphogenesis, because that's what this process is called.