Be it further enacted, That before the beginning of a fiscal year or before a time fixed by the city manager, the head of each department and agency supported in whole or in part by appropriated funds, except the school system, shall submit to the city manager a work program for the year in such form and with such information as he may prescribe, which program shall show the amount of allotments requested by quarterly periods for the fiscal year. The city manager shall review the requested allotments and work programs and may revise, alter, change, or reduce such requests before approving allotments; provided, that such allotments shall be in conformity with salaries established by ordinance and any laws relating to obligatory expenditures. The total of such allotments shall not exceed the total appropriation for each department and agency, and no expenditure encumbrance shall be made in excess of the allotments approved by the city manager. An allotment may be revised by the city manager at any time in the fiscal year. If at any time it shall appear to the city manager that revenue is to be less than the original estimate of revenue on which appropriations were based, he shall review all allotments and may appropriate revisions downward in order to prevent the making of expenditures and encumbrances in excess of probable revenue; provided, that no salaries shall be reduced except by ordinance. If there is a separate city school system, the school superintendent shall have such allotment responsibility and authority with respect to the school budget.