Land means surface of earth including things upon the surface of land, above the surface of Land and below the surface of land. The soil above the surface of Land becomes Immovable Property.
Water collected in ponds or lakes also becomes Immovable Property. Apart from this, water flowing in rivers is also an immovable property because the water flows but remains on the surface of Land.
So, does it mean that everything placed on the surface of the earth becomes part of the land?
No, things become part of the Land if there is an intention to make them part of the land.
In many instances, things are on the surface of land but they are immovable property.
For instance Anchor, a road roller may go a few feets deep into the earth due to its nature ( heavy weight) but they are not considered as a part of Land.