Is zakat obligatory on land purchased in installments with the intention of selling it later at a higher price to buy a home without resorting to usury? Is this method forbidden or harmful to anyone?

There is no impediment to purchasing land in installments if it adheres to the Sharia-compliant regulations. If the intention is for trade, then zakat is obligatory on it every year, provided its value reaches the nisab and a full year has passed over it. What remains of its price is deducted from its value, and the remainder is subject to zakat. This is unless the buyer possesses other non-zakat-eligible wealth that covers the debt's value, in which case the land is subject to zakat at its full value.