Sure looks like one of my western Abies that died of root rot. That can happen very quickly, and fertilizer could exacerbate the problem. But I'm not a plant pathologist, I'm not certain there isn't something else that could kill a plant in this way.

Growing it in a container, I'd have to wonder about the soil media, watering frequency and the amount of fertilizer used. Any or all of these could certainly be a problem if not addressed correctly.

FWIW, watering once a week may be too much or not enough depending on the weather and the potting soil.........

a tree is said to be twice as big underground.. as that you see above ...

i dont need a pic of the whole.. to understand that is a huge plant.. in a tiny pot ...

most likely.. there is no media in the pot.. all roots ...so watering is near impossible ... to perfect

if on top of that.. you fert'd directly to the roots.. if in fact.. there is no media ...

conifers are trees ... and they are not houseplants .... nor are they long term potted plants unless you make them bonsai ...

you dont mention where you are ... but dormancy is imperative with many trees ... and though you might have it on the balcony during summer. what to you do with it during winter dormancy????

trees work in slow motion .... tree time ..... and with evergreens.. it can take a long time for the evergreen needles to dry and brown ... it might be coincidental.. that its browned a month after the fert.. it may have been basically dead since winter or early spring ...

all you can do.. is take it out of the pot.. and look at the roots.. and see if there is any media... and whether you actually rotted the roots off ...

ken