Falling export rates have impacted (on) the country's economy quite considerably.
As noun it means;a powerful effect that something, has on a situation or person.
That effect you can either feel or see. When you only feel, use ‘on’ as a prepostion, as:
The anti-smoking campaign had made quite an impact on young people.
When you want see the impact within something, use ‘in’, as:
A documentary film has been made on the effects of antismoking campaign on the youth. So we will be able to view its impact in the auditorium..
Student or Learner