Why do people put manure on the ground?

If land is being used all the time for growing crops and vegetables, the minerals in the soil get used up and need replacing. So farmers and gardeners put fertiliser on the ground to replenish the soil with all the nutrients plants need.

There are two types of fertiliser, mineral and organic. The mineral fertilisers are manufactured and can be bought. The organic fertilisers are made of plant matter and animal dung, built up over a period of time into a manure heap. Farmers spread this manure onto the earth.
Animal dung is waste products from digested food and contains nutrients which are easily absorbed through the roots of plants. It is best to spread it over the ground when it is fresh so that none of the nutritional value is lost. Sometimes the manure is dampened so that it soaks into the ground more quickly and easily.