To arrive to the right conclusion we have to take into account a number of factors: context, utilization of the ‘verb’ in other Bible occurrences, meaning of the conceptual root at issue (חרץ), and simbology.
The previous verse make us to enter in a symbolic agricultural realm (see, please, also Isa 28:27; 41:15):
“Put in the sickle for the harvest is ripe. Go in, tread, for the winepress is full. The vats overflow, for their evil is great” (ESV)
Alter’s translation is very similar, except the slightly different expressions “Wield the sickle…”, and “Come, go down…”
The last stichus of this verse call us back to our mind the link between the grain’s/grapes’ harvest to a final decision, an irrevocable determination. This concept is present throughout the Bible.
For example, in Pro 22:8 (where there, interestingly, we find also an allomorphic variant of the concept, expressed by the consonantic triplet קרץ, rightly translated ‘to reap’); and also in Jer 51:33 (here, too, is present another linked allomorphic variant, namely,קצר).
Although we don’t lingering over the same symbolic concept illustrated in the New Covenant Scriptures (Matthew 13:24-30; 36-43, about the parable of the ‘good seed & the weeds’, and the final harvest; Apo 14:14-20, with similar views), it is clear that this link between ‘harvest’ and ‘a final decision/determination’ is well established. The Jean Chevalier & Alain Gheerbrant’s Dictionnaire des Symboles confirms this metaphoric usage of ‘harvest’ in the Bible.
Anyway, it is known to all people the iconography of Death wielding a scythe (a kind of sickle) in his hands, as a symbol of a final, irrevocable decision, about life of men.
The meaning of ‘decision, determination’ is confirmed also by others occurrences of the same ‘verb’ used in Joel, namely:
1 Kin 20:40, “And as thy servant was busy here and there, he was gone. And the king of Israel said unto him: ‘So shall thy judgment be; thyself hast decided (חרצת) it.’” (JPS)
Isa 10:22, “For though thy people, O Israel, be as the sand of the sea, only a remnant of them shall return; an extermination is determined (חרוץ), overflowing with righteousness.”
Job 14:5, “Seeing his days are determined (חרוצים), the number of his months is with Thee, and Thou hast appointed his bounds that he cannot pass;”
At this regard, the Robert Alter’s note on Joe 4:14 is enlighting: “’The Valley of Doom’. The verbal stem h.r.ts [the ‘h’ in the original text has a point below it, I do not have this type in my PC, sorry], appearing here in the name haruts, means to pronounce judgment or issue a verdict.”
The 17th-century Bible scholar Johannes Piscator translated in Latin the Hebrew expression החרוץ בעמק, into “in valle triturationis” (‘in the Valley of Threshing’).
So, by the convergence of all the factors examined - context, utilization of the ‘verb’ in other occurrences, meaning of the conceptual root at issue (חרץ), and simbology - we may conclude that the more apt reading of חרוץ - in Joe 3:14 (4:14) – is ‘decision’, ‘determination’.
I hope these notes will be useful for you.