That irrigation and fertilizers contribute significantly to the growth of agricultural output is a common fact. Similarly, investment in irrigation, flood control and drainage is a matter of social overhead capital and hence the role of public policy is also well recognized. What needs, however, to be appreciated is the alternative role that investment in irrigation and fertilizers play as agricultural productivity moves from one level to the other. Unless this is well understood, the associated role and details of the public policy to make this possible cannot be sketched. Both these aspects are dealt with in this note by drawing on the available literature on this subject.