Childrens Illustrated Encyclopedia

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472

Recycling

All living things

eventually rot away,

back into the soil.

The compost heap is a

valuable recycler. in time, it

turns domestic organic garbage such as apple

peelings, banana skins, eggshells, and grass

cuttings into humus, a food supply for the soil.

in this way, valuable resources are recycled.

Potato

tuber

Soil lAyeRS

Soil is formed from several different layers that merge into

each other. on top is a layer of humus, consisting of dead

and rotting leaves. Underneath this layer is the topsoil

where decayed plant and animal matter is broken

down and recycled by insects, fungi, and bacteria.

The subsoil layer, which contains less organic

matter, lies below the topsoil, and above a

loose layer of partly weathered rock.

A hard layer of solid bedrock lies

below all the other layers.

TopSoil

Topsoil is full of burrowing bugs, worms, and

other creatures. it also gives anchorage to plants

with shallow root systems.

SUbSoil

The subsoil layer is reached only by

deep-rooted plants such as trees.

Caterpillar

Soil eRoSion

in overfarmed areas, or where

natural vegetation is removed, soil

is no longer protected from rain or

held in place by roots. Winds blow

away the loose particles as dust, and

rains wash them away as mud.

The land becomes infertile

and cannot support life.

Today, soil erosion

affects more than

198,000 sq miles

(513,000 sq km) in

the US alone.

pARTly WeATheRed Rock zone

This layer of rocks has weathered and

been crumbled into loose chunks

and contains no organic matter.

iF yoU ReAch doWn and pick up a handful

of soil, you will be holding one of earth’s most

basic and valuable resources. Soil teems with

life. A plot of earth the size of a small garden may

contain millions of insects and microorganisms,

plus organic matter from dead or dying plants

and animals. Soil provides the foundation for

roots, a source of food for plants, and a home

not only for burrowing animals, such as moles,

but also for millions of spiders and centipedes.

There are many different types of soil, from thick silt and loose sand, to

waterlogged mud and dry desert. Soil is formed from the wearing down of

rocks and takes many years to develop. each 1 sq in (6.5 sq cm) of soil, for

instance, may take 100 to 2,000 years to form. The quality of soil varies from

region to region. in hot places, such as Africa and Australia, where there

is little rain, the soil is very dry. in temperate regions, such as europe and

north America, much of the soil is rich and fertile. but soil can be destroyed

in just a fraction of the time it takes to form. overfarming the land, for

example, has led to soil erosion in many parts of the world.

Tree roots reach

into subsoil layer.

hUmUS

humus is the layer of decaying leaves

and other plant material in the soil.

Soil

compoST

Fungi, bacteria, worms, and insects

thrive in a compost heap, helping the

contents to decay and be recycled.

Earthworm

Slug Beetle

Snail

Beetle

Centipede

Moles tunnel in the

upper part of rich soil,

where there are many

worms to eat.

Clay

soil

Find out more

Flowers and herbs

mushrooms,

toadstools, and other fungi

plants

Trees

Chalky

soil

Sandy

soil

Types of soil

Soil may be black,

brown, red, yellow,

orange, or cream in

color, depending on

the minerals it contains.

Rich, dark, peaty soil is

ideal for garden plants.

poTATo

All plants, including the

potato, use the energy

in sunlight, mineral

nutrients in the soil, water,

and carbon dioxide from

the air to grow. The potato

plant stores its food reserves

in the potatoes that we eat.

Peaty

soil

FeRTilizeR

Farmers add fertilizers to poor soil.

The fertilizer is rich in minerals

that help the crops grow.

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