Which one of the following is a characteristic feature of cropland ecosystem?

Least genetic diversity is a characteristic feature of cropland ecosystem. A crop land ecosystem will have a major crop cultivated in a given area. It shows the least genetic diversity.

A cropland would have weeds. 

The gradual and fairly predictable change in the species composition of a given area is called ecological succession. It is not observed in cropland ecosystem. 

Cropland would have lot of soil organisms. Earthworms for example are important for fertility and porosity of soil.