Does zakat apply to the total amount (170,000) or only to the personal funds (80,000), in the case of purchasing land for trade with an amount that includes a loan?

If the land is for sale, its value is subject to zakat from the time of its purchase. It should be appraised at its current value at the completion of the hawl (one lunar year), and one-quarter of one-tenth (2.5%) of its value is to be given as zakat. Debt, according to the majority of scholars, reduces zakat on bāṭinah (unseen/indirect) wealth, such as trade goods. Therefore, you may deduct the debt from the value of the land. If a niṣāb (minimum threshold) remains after the deduction, zakat is obligatory; otherwise, it is not, unless you have other surplus wealth beyond your basic needs, in which case you can consider that wealth as offsetting the debt and pay zakat on the entire amount.