The Most

Important Issue

You’ve Never

Heard Of

Land & Soil

Degradation:

Introduction to Issue

Can be argued that land degradation affects

more people (and other living things) more

seriously than any other environmental

problem

Like many things, most familiar, most mundane

is most important and most easily ignored

After all it’s “just dirt”

The Gravity of the Problem

“Let us never forget that the cultivation of

the earth is the most important labor of

man. When tillage begins, other arts

follow. The farmers, therefore, are the

founders of civilization.”

Daniel Webster

Not a New Problem.

Attica (Athens) was no longer

cultivated by true herdsmen,

who made husbandry their

business, and were lovers of

honor, and of a noble nature.

As a result Attica had become

deforested, the soils depleted,

and there are remaining only

the bones of the wasted body –

all the richer and softer parts of

the soil having fallen away. ~

Plato

Since land degradation (unlike desertification) is defined as resulting fromhuman actions, the global introduction and spread of the problem are closely related to the introduction, spread and growth of human populations and their increasing demands on the natural resource base. However, as has been said many times, numbers alone are not the sole cause: land-use practices, which in turn are influenced by technology amongst a range of other factors, are the primary underlying cause.

Although humanity is thought to have originated in Africa’s rift valley region, the first reasonably well-documented instance of land degradation comes from what used to be called Mesopotamia; the irrigated lands in the Tigris and Euphrates river systems. Here, as in other irrigated drylands of North Africa and later Pakistan, California and elsewhere, the main problems were (and are) secondary salinization, related to waterlogging. Associated with this was a serious decline in soil fertility.

The early initiation and growth of urban civilizations in Mesopotamia in the later part of the 4th millennium BC was related to the development of irrigation. The main crop was wheat. Increasing salinity is reported to have caused a shift from wheat to the more salt-tolerant barley: by around 3500 BC the proportions of the two crops were roughly equal, and by 1700 BC wheat had been abandoned completely. Eventually even barley could not be grown and the populations of the kingdoms of Sumer and Akkad had to abandon the area. Historical evidence from other regions in China, the Indus River Basin, South America and Arizona indicates that similar problems permeate our history. The process forced people to shift to other locations which, in turn, also became salinized in many cases.

Land Degradation & Poverty

Closely linked to poverty? How?

As the degree of degradation increases,

crop and animal yields decline and people

have both less to eat and less to sell to

support themselves

“If the soil on which agriculture and all human life depend is wasted away, then the battle to free mankind from want cannot be won.” ~ Lord John Boyd Orr, first Director-General of

the UN Food and Agriculture Organization (1948)

How Big is the Problem? … In 2008, the world's arable land amounted to 1,386

M ha, out of a total 4,883 M ha land used for

agriculture (about ¼ of the earth’s land mass)

United Nations has estimated that about 15% of the

world’s productive farmland has been significantly

affected by some form of land degradation

Arable land percent world

Four Categories

Erosion

Chemical Deterioration

Physical Deterioration

Desertification

1 ~ ErosionThe removal of the nutrient-rich layer

of topsoil by either wind or water

Water erosion can occur in any

climate zone

Mostly in places with higher annual rainfall

Wind erosion occurs most commonly

in arid and semi-arid climates Most erosion subtle… over

time

Every spring the 12 Mile Creek

looks brown… that’s evidence of

annual erosion

Erosion In a mature forest that

is not affected by human activities, the amount of topsoil loss is between 0.004-0.05 tonne per hectare per year.

Relatively minor loss can easily be made up by natural soil-forming processes at work

Insects, decomposition, fungi, etc.

Overall avg. soil erosion for cultivated land in North America and Europe is about 17 tonnes per hectare per year (situation worse in Asia, Africa, South Asia)

300-400 TIMES AS MUCH as in untouched forest

Direct result of change from forest to farmland

Problems on the SlopesCannot be replaced by soil-forming

processes

Soil erosion becomes even worse when hilly

land is used for farming

Steep slopes obvs. accelerate water

Terrain Deformation In the case of water erosion Large or small gullies may be cut into

farmers’ fields

Mass movements (landslides) may occur

Case of wind erosion Dunes or deflation hollows –

depressions created when wind removes topsoil from prev. level area

Land may be over-blown – covered by wind-eroded materials from elsewhere

2 ~ Chemical Deterioration Deterioration of soil as a result of leaching,

salinization, acidification or pollution

A) Leaching To remove soluble or other constituents from by the action of a percolating liquid.

Vital nutrients ( nitrogen, phosphorous, potassium)

can be lost in two ways:

1 – Loss of soil nutrients

Worst in tropical areas where rain washes away soil

and nutrients

Severely leached soils are orange-

red in colour

Dominance of oxides aluminum and iron in soil

Chemical Deterioration cont…

Leaching is worst in Tropical areas

Worst of all if dense layer of vegetation has been

clear-cut for farming

High yields for few years

Organic material still in soil

Leaching soon strips soil of most essential nutrients

2) Growth of crops

Soil nutrients lost through

farming practices, part. if

same crop grown year after

year

monoculture

Chemical

Deterioration cont…

B) Salinization

An increase in the

concentration of soluble

salts in the soil to the point

where the soil becomes toxic for plant growth

Greatly accelerated by excessive irrigation

Water used for irrigation carries dissolved salts

that will be left in the soil when the water

evaporates

Salt concentration will eventually reach

dangerous levels (if not properly controlled)

About 1/8 of all irrigated land in the world has

been degraded by severe salinization

Chemical Deterioration cont…

C ~ Acidification

Land can become acidified by the use of

excessive fertilizers or because of poor drainage

Chemical Deterioration cont…

D) Emissions

Land can be polluted by emissions from

nearby industries

Or by dumping of liquid or solid wastes

Sludge – treated sewage waste

3 ~ Physical Deterioration Degradation of land caused by

compaction, waterlogging, or subsidence

Three ways:

Soil can be compacted by the use of heavy machines or by the trampling of herds of animals

Waterlogging obvs., after floods recede from an area, can damage land

Subsidence – sinking of land – can be caused when a significant amount of water is removed from the water table

4 ~ Desertification Special type of land degradation – refers to the

results of degradation rather than the causes

Occurs when human activities reduce the productivity of an arid or semi-arid area to the point that it resembles a desert

As much as 40% of the world has climates dry enough that they face the possibility of desertification

The Green Wall…Why is Africa building a Great

Green Wall? BBC News (on

youtube)

https://www.youtube.com/watch?v=4xls7

K_xFBQ&feature=youtu.be

BREAK! Two hunters are out in the woods when

one of them collapses. He doesn't seem to be breathing and his eyes are glazed. The other guy whips out his phone and calls the emergency services. He gasps, "My friend is dead! What can I do?" The operator says "Calm down. I can help. First, let's make sure he's dead." There is a silence, then a gun shot is heard. Back on the phone, the guy says "OK, now what?"

We’ve learned of the types of

land degradation…

But what of the causes?

Five Main Categories

Deforestation

Overgrazing

Unsustainable agriculture

Overuse of natural vegetation

Urban/Industrial Pollution

DeforestationMore than just a few trees cut down…

When large forest areas are cleared for

agricultural use, particularly in tropical

rainforests

“slash and burn” agriculture

Impacts:

Degradation of soil

loss of habitat for millions of species. Seventy

percent of Earth’s land animals and plants live

in forests

Disruption of water cycle and carbon cycle

Overgrazing herbivory(animal comsumption

of plants) that extracts an

unsustainable yield of floral

biomass from an ecosystem;

More simply, too many grazing

cattle, sheep, or goats can

destroy vegetation beyond its

ability to recover

Soil then exposed to erosion and

leaching

Estimates of overgrazing

worldwide are on the order of

1/3 to ¼ of all rangeland

Unsustainable Agricultureo Most modern agr., if carried out too intensively so

soil cannot renew itself, reduces nutrient levels and

– in dry areas – may result in salinization as well

o A.k.a. “Agricultural mining”

o Monoculture – large-scale operations growing one

variety of one crop annually

• Healthy ecosystems require complex and

diverse flora and fauna

Urban/Industrial Pollution Pollution from industrial/commercial factories,

warehouses, mines, etc. can foul the soil

Pesticides, heavy metals, sludge, etc.

E.g., phosphate fertilizer which contains small amounts of cadmium and lead is widely applied

Soil contaminated from agricultural and industrial wastes will produce unhealthy food.

Heavy metals and other toxins enter the food chain & are consumed by human beings.

biomagnification

Overuse of Natural Vegetation In many developing countries (Near Core and

Periphery), people rely on trees and shrubs for fuel

and for building materials

If pop. dens. of an area becomes too high,

overuse of vegetation can have an impact similar

to that of overgrazing and deforestation

“A nation that destroys its soils destroys

itself. Forests are the lungs of our land,

purifying the air and giving fresh strength

to our people. ”

Franklin D. Roosevelt