How is Zakat paid on olives in the case of splitting the harvest in half and selling a large portion of one's share before the remainder reaches the Nisab?

The mentioned transaction (harvesting part of the fruit in exchange for some of it) is a matter of scholarly disagreement, with the majority prohibiting it, and this is the issued fatwa. Therefore, the transaction must be annulled and converted into a rental agreement with a known wage if possible. Otherwise, the zakat on the fruit becomes obligatory for its owner at the time the fruit begins to ripen. If you are merely laborers, then there is no zakat due on what you receive as wages.

However, if the transaction is a musaqat (sharecropping) agreement and you are entitled to half of the fruit, then zakat (one-tenth or half of one-tenth) becomes obligatory upon you if each individual's share reaches the nisab (five awsuq). The zakat is to be paid from the remaining fruit, or its equivalent amount purchased if all of it was sold.