Could be fine. Maples grow in flushes, keep it watered and mulched, wait and see what the current flush develops into. Since plant is growing away nicely now (above the ground, at least), at this stage it seems root deformity would most likely only become a problem many years from now, if it resulted in girdling and constriction. If in doubt expose roots and correct when leaves are off during dormant season.

hand trowel ... dig 3 or 4.. 6 inch holes... AND FIND OUT IF THERE IS ANY MOISTURE AT DEPTH ... when i run irrigation on trees... i run it 6 to 8 hours on my sand ... because that is what is required with my engineered system of x gallons per hour... taking into account my sand... how did you come up with your number of hours??? and the way to find out.. is to dig the holes.. and discover how its working... you dont say how large the transplants are ... but if they are over 6 feet... you need to have the entire root mass planted dampish ... but not sodden.. for up to 3 years ... and it isnt surprising.. it appeared.. when the heat hit ... it has absolutely nothing to do with fert ... and as far as i am concerned.. you NEVER fert trees ... especially if you fert your lawn ... the tree will get/steal all it ever needs ... one might suggest that a soil test will tell you if anything is lacking.. i feel its much simpler to look around and see if trees... shrubs.. plants.. are thriving.. in general.. and if they are.. then the soil is good enough for your trees ... pic is you want more info ... ken

let me put it this way ... i hate poplars.. lol ... the problem you saw in 5 or 10 years.. on the poplar.. you WILL SEE on the maple.. in 30 to 50 years ... as to your age.. and if that will be an issue in 30 to 50 years.. i do not know ... of all the trees in this wide world.. i wonder.. why you are limiting yourself.. to ONLY these two options ???? what about oak??? where are you .... and are you open to other options???? another way to say this.. is that anything that claims to be FAST GROWING.. which is the ONLY salable point of a poplar ... is going to be fast to be a problem.. and fast to die ... as you have learned ... and one might suggest.. if this maple is marketed under the same idea.. of fast growing.. well.. my gut tells me.. its might be another problem tree .. but again.. its the time frame of how fast it will all happen ... ken ps: i hate maples too.. lol .. but that is because i can not garden under them ... and if you had poplar.. i will presume.. you werent gardening under them anyway .. so it doesnt matter ... but if you have any inclination ... to want to do such ... you need something beyond a maple .. pps: you will probably be killing root suckers from that poplar.. for upwards of 3 years.. even if you have the stump ground out ... they will need to be snipped and treated with roundup or stump killer.. until they stop coming back ... let us know when this happens ....

In the latter case if you are in an area with unsuitable autumn weather or soils this can affect results with fall color of maples. The Tatarian maple cultivar is selected for use in areas with alkaline soils etc. but red maples do not color well in alkaline soils - and fall color of seedling red maples varies from yellow to nearly purple depending on the genetics of the individual seedlings. Plantings or wild stands of genetically distinct individuals (rather than multiple specimens of a clonal cultivar) can be a kaleidoscope of different colors in autumn. Root damage I don't see as being related. In fact, if you stuck them in using care to avoid root damage that could have been a mistake. The most important thing when planting a tree is to make sure the roots are spread out in the hole and not kinked or circling, and that the same soil is present throughout the hole, with no zones of differing soils. Intact original soil balls are not desirable unless the backfill soil and the soil around the hole all happen to be the same as the soil inside the rootball - not a usual circumstance.