Do you have to pay social security tax on farmland you sold or is it just income tax?

Social Security tax or self-employment tax is not payable on capital gains. You may also get a reduced rate based on how long you owned the property. I strongly suggest that you go to a professional tax preparer to complete a return with a property sale. You will report this using form 1040 and Schedule D for the property sale if it was not used in a business. If it was used in farming or other business use this will change the forms you are required to file.