Is it permissible to pay Zakat on the profits from buying and selling crops at a rate of 2.5% of the profit immediately, and what should the questioner do regarding past years if this action was incorrect?

Zakat is not obligatory on wealth unless it reaches the nisab (minimum threshold) and a full lunar year (hawl) has passed on it. The nisab is approximately equivalent to 85 grams of gold or 595 grams of silver. If the wealth does not reach the nisab or a full year has not passed on it, then no zakat is due. Whatever money you spent with the intention of zakat before the completion of the hawl is a rewarded charity, and according to the majority of scholars, it is permissible to pay zakat in advance. However, if zakat becomes obligatory, then both the principal and the profit must be calculated, and one-quarter of one-tenth (2.5%) of it must be given out. If you paid a sum with the intention of zakat before the completion of the hawl, it will be deducted from the due zakat. It is obligatory to hasten in giving out the due zakat, as it is the right of the poor and the needy.