The agricultural practice of irrigation leaves behind which pollutant in the soil?

A. Pesticides

B. Acidic compounds

C. Salt

D. Nitrogen compounds

I think the answer is A pesticides. Pesticides and fertilizers have been the earliest sources of agricultural pollution. Modern day pesticides and fertilizers have to deal with the local pests that have existed for hundreds of years along with the new invasive species. This means they are therefore laden with chemicals that are not found in nature, this in turn leads to pollution, since when sprayed they don't disappear completely.

The answer is indeed C. salt (apex)