Nute burn can manifest in a couple ways, but a lot of times if you are overfeeding, the leaves will get a darker green, and then sometimes with the dark green you will see the leaf fronds begin to curl under, forming a "claw shape". Sometimes neither will happen and you will see just the tips of the leaf fronds turn brown and dry like someone held a small flame to them to burn the tips. If you are seeing the dark leaf and the "claw" shaped leaves, that is the plant warning you that it has all the Nitrogen that it can stand. That is when you need to give it just straight water for a week to 10days until you see that begin to back off some, then the next feeding, cut the nutes by 20%. If you are in organic soil, overnute is fairly hard to do but not impossible. The soil would have to be very hot, and it would require either transplanting or flushing to try to remove some of the chelated nutrients. However the jury is still out on how well flushing works in organic soils.