Answer:
C. overfarming
Step-by-step explanation:
The problem that might likely occur with farming a plot of land year after year without any fertilizer is over-farming. 
- Over- cultivation is the excessive use of a land. 
- This results into nutrient depletion of the land as a result of pressure on the minerals in the soil. 
- Over- cultivation often leads to land degradation. 
- This makes the land unfit for agricultural purpose and a risk of being a desert. 
- One leading cause of over farming is overpopulation. 
- When too many people are farming and they cannot make room for crop rotation or bush fallowing, the pressure on the soil becomes too much.