Question: what are the four main causes of land degradation?
Answer: Deforestation: Forests play an important role in maintaining fertility of soil by shedding their leaves which contain many nutrients. ... 
Excessive Use of Fertilizers and Pesticides: ... 
Overgrazing: ... 
Salination: ... 
Water-logging: ... 
Desertification: ... 
Soil erosion: ... 
Wasteland: