The insect propagates best near "disturbed land," that which is being cultivated by humans.
I saw this type of sentence. Do you use this kind of syntax. Would it be possible that it is colloquial?
Some explain that "that" following "disturbed land," is the apposition and also the antecedent of the "which". I often see "that which" phrases but these did not have this apposition like structure.
This kind of syntax is certainly used, and I don't have the impression it is colloquial.
What is confusing about your example sentence, is that you punctuated it as is disturbed land is direct speech, but in reality, you're quotes are what is sometimes called scare quotes. In that case I would not put the comma inside the quotes:
The insect propagates best near "disturbed land", that which is being cultivated by humans.
Alternatively, do not use scare quotes at all. Disturbed land has a special meaning in this context, which is indicated by the quotes, but you can convey the same thing with italics:
The insect propagates best near disturbed land, that which is being cultivated by humans.
That said, let's look at the that which construction.
I would agree that that [land] which is cultivated by humans is the apposition of disturbed land. They describe the same concept, the land where the insect propagates best.
That is indeed the antecedent of which, but it might be easier to realize that land has been elided (as I indicated earlier):
That land, which is cultivated by humans.
In this case, that land is the antecedent of which.
To illustrate the apposition, we can inverse the two parts:
That land, which is cultivated by humans, is called disturbed land.
And even in the complete sentence:
The insect propagates best near that land which is being cultivated by humans, "disturbed land".
In this version, we could omit that without changing the meaning of the sentence much.
The sentence is fine. It's rather the opposite of colloquial—most people don't talk like this in everyday speech.
We can analyze it as ellipsis, if we like:
The insect propagates best near "disturbed land," that land [ which ___ is being cultivated by humans. ]
Here, the relative clause which is being cultivated modifies that land. The phrase that land plays the subject role in the relative clause.
Taken as a whole, that land which is being cultivated by humans is a (non-restrictive) appositive phrase which defines the term in quotes, "disturbed land".
