The city school budget submitted by the board of education through the city manager to the city council shall include estimates of all school revenues, as well as estimates of expenditures necessary for the operation of the school system for the next fiscal period. Neither the city manager nor the city council shall have any authority to modify or delete any item of the school estimates, and the council shall have the power to modify only the total amount of the school budget, except that in no event shall a reduction in the school budget exceed the total sum requested by the board of education from current city tax revenues. Such budget estimates shall not include any requests for the purchase of land, and the purchase, construction, reconstruction, or major alteration of any building for school purposes. Requests for such improvements shall be transmitted to the planning commission for review and incorporation into the capital improvement program.