What is the commission rate for realtors when selling only land, (no house)?
There is not a set commission rate for Realtors regardless of the type of property, size of property etc. When selling a home, 6% of the sales price is a generally accepted as a 'normal' level. At the same time, that 'normal' level may vary geographically between 4 and 7% of the sales price. At the same time, there are many transactions that use a different structure, depending on the quality of the Realtor, the length of the listing, and sometimes the price of the property for sale.
Sometimes commission levels are defined in flat dollar amounts as opposed to a percentage of the sales price as well. Commission prices do not widely vary just because a piece of Real Estate doesn't have a home on it.
My suggestion would be to contact several agents in your area and speak to them directly about what their fee would be to list the property. Because Real Estate is so geographically focused, you will receive the best information by talking to Realtors in your local market than you would in a general question.