A person who did not pay zakah for several years then repented, but does not know how much his land produced, how should he pay zakah?

Abu Ishaq: All right, regarding the obligatory zakah, of course, the answer will likely become clear from this question. From this answer, it is understood that a man remained without paying zakah for a long period of several years, then he repented and turned back to Allah, and he wanted to pay the zakah. Of course, it is obligatory for him to pay it.

The Shaykh : It is necessary.
Abu Ishaq: But he had agricultural land, so he does not know how much it produced as a yield. How does he determine the amount of zakah to pay?

The Shaykh : By the preponderance of opinion, as is the reference in all matters that involve such ambiguity, one uses the preponderance of opinion to estimate it. For example, he exerts effort to estimate it; there is nothing specific.
Abu Ishaq: Regarding zakah, is it paid on the capital and the profit, or on the profit only?

The Shaykh : Any wealth, meaning the two types of currency, for example.
Abu Ishaq: The two types of currency together.

The Shaykh : I think this issue is related to a well-known issue among jurists... and there is also a famous disagreement in it. It is when the nisab is reached and a lunar year has passed over it, and during the year, an amount of wealth or multiple nisabs is added to the nisab, but a lunar year has not passed over each of these other nisabs. So when he wants to pay the zakah, does he pay it on the first nisab over which a lunar year has passed only, and then each of the other nisabs has its own calculation? Or does he pay it on the total of what he has, which is the first nisab plus the other nisabs over which a lunar year has not passed? So in this issue, there are two opinions. Some say that each nisab has its own calculation; and according to this opinion, he pays the zakah on the first nisab over which a lunar year has passed. The other opinion is that he pays on all this wealth he has, both that over which a lunar year has passed and that over which it has not passed. And the one I choose is this one.
Abu Ishaq: The second one.

The Shaykh : The second one; because observing that each nisab does not require zakah until a lunar year has passed over it is a matter that conflicts with the saying of Allah the Exalted: . It is very difficult, especially for large merchants, to calculate for each nisab, as hundreds of nisabs will accumulate with them, if not more than that, and that would be burdensome for them. This is the first point, and the hardship is removed by the explicit text of the Qur'an. And secondly, this is more beneficial for the poor and the needy. And although I do not make this second matter a legal proof, if it were not for the first proof, I would not have said the second one, but the second one is as a corroborating witness, not as a proof and evidence. Based on that, I think this is the answer to your previous question, is that so?
Abu Ishaq: If Allah wills.

The Shaykh : If Allah wills.