How to Determine Land/Improvement Split for Depreciation?

[Marco G.]

How do you decide on the land/improvement split on new acquisitions?  My purchase price is about 30% higher than the tax appraisal basis, but the county conducted an tax appraisal in 2015 (last one had been 2012).  Can I keep the land value and add the difference between their appraisal and my purchase price to improvement value?  Do I have to use purchase price, or can I use my (higher) loan appraisal?  No significant improvements were made and those that were will be separately depreciated or written off.