How is the Zakat due on money invested in agriculture and partnership financing in a brokerage firm to be paid?

"Money invested in a permissible project is subject to zakat on both its principal and profit, at a rate of one-quarter of one-tenth (2.5%) upon the completion of a full lunar year. As for money invested in a prohibited business, the profit is an illicit gain that must be disposed of in charitable causes, and only the principal is subject to zakat. Onions are not subject to zakat unless they are intended for trade and a full lunar year passes over them or over their price, provided it reaches the minimum threshold (nisab)."