Is Zakat obligatory on lands outside the city that do not have legal deeds, but merely bills of sale, and upon which Zakat has not been paid for years? And how should one proceed if Zakat becomes obligatory, given existing disputes over these lands that prevent the determination of their price?

If you purchased land with the intention of trading it, and it became subject to trade zakat (definition), it should be appraised annually, and one-quarter of one-tenth (2.5%) of its value should be paid. However, if you are unable to sell or dispose of it due to disputes with the municipality, zakat is not obligatory on it during this period, due to the incompleteness of ownership. This resembles a debt owed by a procrastinator or an insolvent person. Sheikh Ibn 'Uthaymeen issued a fatwa (definition) stating that whoever believes zakat is not obligatory based on the fatwa of a trustworthy scholar is not required to pay zakat. As for whoever believes zakat is obligatory, they must pay it, except for the years during which they are prevented from disposing of the land, because it resembles debts owed by an insolvent person.