I'm not understanding your concern with casualty loss here. Did you have a casualty loss for which you were NOT reimbursed for by the insurance company maybe?
Generally, the only thing that has a value for the land, is the rental property itself, and that's it. All other assets/property improvements will have a total cost, and zero value for the land, unless the improvement was to the land specifically - which is not common. So property improvements should not, and will not have a land value. Example:
Rental property itself cost $100,000 of which $30K is allocated to the land. So $70K will be depreciated over 27.5 years.
Later, I put a new roof on the property at a cost of $10K. When the asset is entered into TurboTax the cost is $10, and the value of the land is zero. So the $10K for the new roof is depreciated over 27.5 years. There was no land improvement here. Only an improvement to the structure.
TurboTax has a completely separate selection in the Assets/Depreciation for land improvements. Since land is not depreciable, land improvements only add to the cost basis, but are not depreciated.
Remember, depreciation is based on the *lesser* of what you paid for the property, or it's FMV at the time it was placed in service. For most, what they paid for the property will be the lesser amount.
