The appropriate governing board shall have authority to grant sabbatical leaves to faculty members at state institutions of higher education for the purpose of permitting them to engage in graduate study, research or other activities calculated to improve their teaching ability. Such leaves shall be granted only in accordance with a uniform plan adopted by each governing board and shall be subject to such reasonable rules as each governing board may prescribe. Any plan adopted by a governing board shall not provide for the granting of sabbatical leave to any faculty member who has served fewer than six years at the institution where presently employed, nor shall such leave be for more than one half the contract period at full pay or a full contract period at half pay. Any faculty member receiving a sabbatical leave shall be required to return and serve for at least one year at the institution from which the leave was granted or to repay to the institution the compensation received during such leave. Any faculty member returning from leave shall be reinstated at the academic rank held prior to such sabbatical unless promoted to a higher rank and shall be entitled to such salary and any increases thereto appropriate to the rank and years of experience of such faculty member. Compensation to a faculty member on sabbatical leave shall be paid from the regular personal services appropriations of the institution where employed.