Sometimes cash (or cash equivalent) can be used for collateral, but that is extremely unusual (for example, if you have $15k in long term CDs and want to borrow $15k with the CDs as collateral).
If you are wondering whether you could buy the land for cash and then later get a mortgage on it -- maybe, but you'd have to be able to qualify (income, credit score, etc.). Banks don't want land. They want to get paid on the agreed-upon repayment schedule. So even if you have collateral worth the value of the loan, you would still need to qualify according to the bank's standards for similar loans.