My research has indicated 乍 is related to soil and farming, but I have seen other sources claim it's a collar of a robe. The meaning in English is "suddenly" - I assume this to be a phonetic loan. I'm just so curious as to the original meaning! Any help would be vastly appreciated :)
怎 zěn (also zě) contains 乍 zhà and 心 “heart, mind,” which suggests that its original meaning is a modal particle. 乍 gives the sound.
So, yes, in 怎:
乍 zhà is a sound component.
You will find it plays as similar role in the following characters:
The only character that you will find where it has any etymological semantic root is 作:
作 zuò: (orig.) to cut down a tree with a blade (now written 柞); make; work; compose, write; act, perform
In the original sense of the word.
I assume this to be a phonetic loan.
I don't think so.
乍 - 会意。小篆字形，从亡从一。本义:忽然.