Must zakat on produce be paid from the produce itself and at the time of harvest, and to whom is it due, and should it be paid to the ruler even if he is unjust, and does the owner of the produce calculate and distribute it himself to its rightful recipients as mentioned in the Holy Quran?

Zakat (definition) on fruits is given from the fruits themselves when their ripeness becomes apparent. The obligation becomes firmly established when they are gathered in the threshing floor. It must be distributed immediately to one of the eight categories of those eligible for Zakat. It is preferable for the owner of the Zakat to distribute it himself.