where on tax return to improvements to land input? Adjust the cost basis?

Yes, these improvements would be added to your cost basis for the sale of the land.  Land is considered investment property if it is not part of a home sale.  Land sales are reported by using the following instruction.

1. Wages & Income, then scroll down to Investment Income and select Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B)
2. Respond "yes" to Did you sell any investments?  You'll then be asked Did you get a 1099-B or brokerage statement? answer "no."
3. Enter one sale at a time
4. Enter Land Sale Information 
5. Continue to follow the prompts to complete your sale
6. See the image below for assistance.