Is zakat obligatory on the remaining amount of money that reached the nisab, after half of it was paid as a down payment for buying land?

If the money reaches the nisab (threshold) and a year passes over it before the down payment is made, then zakat of 2.5% is obligatory on the entire sum. However, if the land purchase and down payment occur before the year is complete, and the remaining amount does not reach the nisab, then there is no zakat on it. If the remainder does reach the nisab, then its zakat becomes obligatory if it remains in the possession of the inquirer when a year passes over it, even if he were to borrow to complete the price of the land.