Soil
Soil is the top layer of the earth's surface. lants and trees grow in it. It is the main source of food for the plants and forms a strong base for roots to hold the plant in the soil.
What causes soil to become worthless?
(1) The repeated use of the same land for the same crops, over-cultivation, the buring of grasslands and forests, and road construction.
(2) Floods, drought and the gradual removal of top soil by erosion.
(3) Salinization and released by industrial activity.
Salinization happens because of poor control of the movement of water or natural disasters, such as the invasion of the sea into farmland and the movement of underground water to the surface of teh soil.