Explanation:

Ans. Eliminate parasites which have selective hosts 

The goal of crop rotation is to reduce the amount of the pest population present in the soil. Some pathogens that cause diseases survive in the soil from year to year in one form or the other, usually as sclerotia, spores, or hyphae. Continuously cropping the same crop builds up the population levels of any soil borne pathogen of that crop that may be present. The populations can potentially build up so large that it becomes difficult to grow that crop without yield losses. But by growing a crop that is not a host plant for that pathogen will lead to the pathogen dying out and its soil population levels lowering. Most pest populations will decline in two to three years without a suitable host. Rotating to non-host crops prevents the buildup of large populations of pathogens.