"Section 11.    Registration fees for part of year. — If any application for the first registration is made during the first quarter of a calendar year, the total annual fee for that year shall be paid.

"If such first application is made during the second quarter of a calendar year, three-fourths of the annual fee for that year shall be paid.

"If such first application is made during the third quarter, one-half of the annual fee shall be paid.

"If during the fourth quarter, one-fourth of the annual fee shall be paid.

"This section shall not be construed to allow quarterly renewals of registration in order to avoid payment of fees in advance for the entire year: Provided, however, That owners of motor vehicles dedicated solely to agricultural purposes may register the same monthly for such months when the said motor vehicles are to be actually used."