What is the ruling on selling crops (like wheat) on deferred payment terms before harvest, and is it permissible to do so before the fruit appears, and what are the conditions for this type of debt transaction, and what is the ruling on someone who does this while intending to cultivate, or who does not possess any crops at all?

What you have mentioned has two scenarios:

First: That it is in the form of selling the fruit itself. This is not permissible unless after its ripeness becomes apparent and its grains harden.

Second: That it is in the form of salam (forward buying), by selling something from the fruits described in a liability and not specifically designated. This is permissible under the conditions of salam.