During the past few decades, we have begun to recognize the global significance of
almosi everýthing we do. Economic development or stagnation in one country affects
the economy of all of its trading partners around the world. Worldwide communication
networks provide us with ready computer access to information, knowledge, and news
from everý coínerof the globe. As a consequence, actions of each country, each community,
or even each individual can have global implications.
This globat perspective is equally pertinent for soils. Soil particles picked up by jhe
wind duřing spilng tillage in the Great Plains states can be detected in the rainfall in
the eastern United States or even in Europe. Likewise, excess salts, nitrates, or phosphates
in the drainage water from soils in one nation can make the water unfit for use
in another nation downstream. Changes in soil productivity in one area affect food
security and food prices, as well as biodiversity and water quality, in both nearby and
distant places.
This growing global perspective is paralleled by the growing acceptance of the
ecosystem concept as the prime basis for decisions on natural-resouíce management.
This concept reČognizes that the world is home for a series of communities of living
organisms that interact with each other and with the environment at all scales, from
théglobal terrestrial ecosystem to the ecosystem of a farm pond. Furthermore/ components
of one ecosystem may be impacted by other associated ecosystems, For example,
an ecosystem in a downstream pond certainly may be affected by the chemjcals
Čomingfrom an ecosystem involving an upstream se\^/age plant or an overfertilized
farm field,
Soils are integral components of agroecosystems, forest ecosystems, and grassland
ecosystems. Likewise, they influence downstream freshwater and coastal ecosystems, as
well as urban ecosystems. The ecosystem approach continually reminds us of the interaction
among physical and biological entities in our environment, We cannot clear
forest or range land, lime a soil, add a ney/ irrigation scheme, or apply domestic or
industrial \^/astes to a soil without influencing that soil and all soil organisms and
higher plants growing in or on the soil. Likewise, how we manage plant communities
influences the long_term stability and quality of the soils in which they grow.
871
20. l
In previous chapters \^/e concentrated on the chemical, physical, and biological pro
cesses that may occul in various ecosystems involving soiis, and on the action that indi_
vidual land users might take to influence these processes. We now turn to the global
implications of local land use decisions, and how these decisions affect the quality or
health of the soil-which, through various ecosystems, affects the well-being of humans
and all other living organisms.
THE coNcEPT oF soll QuALlTY/§olL HEAIIHl
From the beginning of time, humans have evaluated the soils on which they work, plar.
and live. Terms Such aS "gOOd," "bad," "woln-out Soils," "productive," or "unproductive"
soils have always been used. In recent years, scientists and users of the soils har-e
realized that many of the world's soils are degrading, and they want to better understand
and reverse that degradation. They,want to learn how to improve the quatity nct
only of degraded soils, but of other soils as well. Also, they want to provide farmers anc
natural resource planners with simple means of comparing the quality of soils from one
ecosystem to another.
To make such comparisons meaningful, and to better understand how the fu]]
potential of a given soil can be realized, soil scientists are using the concept of soil quallFor
reviews on soi1 health and soil qualiý, see Doran, et al. (1996) and Doran andJones (1996)
FlGURE 20. l Schematic píesentation of the definition and functions of soil quality or health, along with examples of inclicator
Ploperties (soil and otherwise) that can be used to measule the quality or health of a soil. The definition of soil quality is in bold
Print, the expanded functions in normal print, and the categolies of indicator properties supporting each function are In italics.
For simPlicity, many interdependencies among soil quality functions ale not shown (e.g., protection of surface water quality is
PartiallY dePendent on lesistance to soil erosion, and so forth). As more knowledge is gained, additional and more ,p".ifi. irrdicator
propelties wi1l likely be added to the 1ist. [Modified from Harris, et al. (1996)]
solL 8uALlry/HEALTH
Capacity oía soil to:
sustain plant and animal productivity
Protect ground/
suríace
water quality
5oil properties
. Nutríents
. Water
. Toxícants
. Pathogens
. Sorptíon
. Precípítatíon
. Decomposi
tion
Water
propertíes
. Oxggenatíon
. Sedíment
. Díssolued
chemícals
. Other
Soíl properties
. Nutríenfs
. Water
. Toxícants
. Pothogens
. Gos
exchange
. Sorptíon
Air
properties
. Goses
. partículates
. Oíher
5oíl properties
. Organíc
matter
. structurql
stabílíty
. Water
. Soíl
roughness
. Texture
Climate
characters
. Wínd
. Eoapotrans-
pkotíon
. Precípítatíon
Soíl propertíes
. Actíue O.M.
. Mícrobíol
abundance
. Water
. Macrobíal
abundance
. Pathogens
. Nutríents
Community
characters
. Specíes
díoersítg
. Functíonal
dítsersitq
. Resílíence
soil propertíes
. Organíc
motter
. Nutríents
. Water
. Toxícorrts
. Pathogens
. structural
stabílítlJ
Plant
properties
. Yíeld
. Qualítg
. Other
5oil properties
. Organíc
matter
. Nutríenr§
. Water
. Toxíconts
. Pathogens
. structurql
stabílítg
Animal
properties
. Yíeld
. §ualítu
. Other
Soil properties
. Nrríríents
. Toxícants
. Pathogens
. Aesthetíc
relatíons
Human
properties
. Health
. other
872 GIabaI Soíl§ualitg as Affected bg Human Actíuítíes
íntroductory s]ide show on
soil qr-rality or health:
§lWWag.ohio-state.edu/
- prec/soíl/slides/
ity or soil health.2 Soil quality considers the soil's fitness for any given function/ such
as those concelned with biological production, road or building foundations, oI dis_
posal of \^/astes. However, we will emphasize the soil's fitness to serve three functions:
(1) as a medium to promote the growth of plants and animals (including humans),
while regulating the flow of Ývater in the environment; (2) as an environmental buffer
that assimilates and degrades environmentally hazardous compounds; and (3) as a factor
in enhancing the health of plants and animals, including humans. .
These three broad issues lead to the following definition: Soil quality is the capacity
of a soil to function within (and sometimes outside) its ecosystem boundaries to sustain
biological productiviý and diversity, maintain environmental qualiý, and promote plant
and animal health. The relationship between the definition of soil quality or health, its
functions, and criteria for its measulement is shown in Figure 20.1.
Assessíng Soíl 0ualíty
The soil's ability to perform a desired function is often dependent on one oI more
dynamic physical, chemical or biological processes that occur in soil ecosystems. Examples
of such dynamic processes include the leaching of nutrients or pollutants through
the soil to groundwatel, the processes of soil erosion, exchanges between air and water
that influence the soil's ability to perform, and the breakdown and synthesis of organic
matter in soils. It is not always possible to measure directly the rates of these plocesses/
but we can measure specific soil properties that are indicative of these rates. We can also
use these measuIements in simulation models to predict future changes in process rates
and, in turn, soil quality. The properties measured are termed indicators. A minimum
data set of such properties for the determination of soil quality or health is given in
Table 20.1.
Research is underway to tly to measule quantitatively a soil's ability to perform a
given function. This is done by developing a soil-quality index for each soil ecosystem.
The index is arrived at by weighting each indicator in accordance with its presumed
2These terms are often used interchangeably in scientific literature and in the public press. Soil health is
best used to lefel to the condition of a soi] as a result of its management. Soil qualíty may refer to both
permanent soil properties and soil condition.
TABLE 20.1 Possible Minimum Data Set of Physical, Chemica| and BiologicaI lndicators
íor Determining the Quality or Health oía §oil
Other supporting indicators can be used to help establish the validiý of the measurements. It may be
possible to combine the values for each indicator into a single soil-quality index number. The weight
given to each indicator woulcL be determined by the particular functions of the soil.
Indicator Rationale for its use
PhysicaI
TextuIe
Depth of soil and íooting
Infiltration and soil bulk density
\Vater-holding capacity
Retention and tlanspolt of water and chemicals
Estimate of productiviý potential and erosion; normalizes landscape and geographic variability
Potential for leaching, productivity, and erosion
Related to Watel Ietention, tIanspoTt, and elosivity
Chemical
Total soi1 OM
_{ctive OM
pH
Electrica1 conductivity
Extractable N, P and K
Defines carbon storage, potential fertility, and stability
Defines structura] stability and food for microbes
Defines biological and chemical activity thresholds
Defines plant and microbial activity thresholds
Plant-avai]able nutíients and potential for N 1oss; productivity and environmental quality indicators
Biological
vicrobia1 biomass c and N
Potentially mineralizable N
Specific Iespilation
Macroorganism numbers
Microbial catalytic potentia1 and early warning of management effect on organic matteI
Soil productivity and N supply potentia]
Microbial activity peI unit of microbia] biomass
Potential influence of such organisms as earthworms
Modified from Doran, et al. (1996).
THr CoNcrpT oF SolL Qunllry/Soll HEALTH 873
**E,;růť
importance in carrying out the function desired. A summation of the weighted indicators
gives rise to the soil quality index as the example that follow illustrates.
Soíl-§ualíty lndex for Erosíuítg:An Example
A soil-quality index as related to soil erosion could be derived from the information
in Table 20.2. Fout functions of the soil in resisting water erosion are depicted: (1)
accommodating water entry, (2) faciliťating water transfer and adoption, (3) resisting degradation,
and (4) sustaining plant growth. The relative weight of each soil function in
resisting erosion is indicated, 500/o assumed to be due to accommodating \^/ater entíy,
35o/o to resisting particle degradation, lOo/o to facilitating \^/atel transport and absorption,
and 5olo to sustaining plant growth. Measurements that could serve as indicators
of these four soil functions are shown along with their respective weights, Note the
many physical, chemical, and biological properties that can help one assess the ability
of a soil to resist erosion.
The analytical data for the major indicators, along with their respective weights, can
be used to develop an overall soil-quality index relating to water erosion. For example,
the component of such an index relating to resisting degradation was found to rate at
0.84 (out of a possible 1.0) for an Iowa soil where sustainable farming practices were
being followed, compared to only 0.60 for an adjacent field where conventional intensive,
high-input practices \^/ere being used. Such attempts to quantify assessments of soil
quality are most welcome.
Tíme- and Place-SensítíueFunctíons
The relative importance of different soil functions and the weights given them will vary
from one time to anothe1 and from one location to another at a given time. This is
illustrated in Table 20.3, which shows that in 1900 the food- and fiber-production function
was paramount (highly weighted) compared to the five other nonproduction functions.
But in our day, the elements concerned with the environment are perceived to be
relatively more important, especially in the industrialized countries where food securi§
is reasonably assured. The broader ecological roles of soils are becoming more widely
TABLE 20.2 Four Possible Soil-Quality Functions and Their Relative Weights
in Determining the Resistance to Soil Erosion, Along with Measurable
lndicators for Each Function and Their Weights
Note that with the exception of soil texture, most of the indicators are properties
that can be significantly influenced by soil-management practices. Note that
accommodating water entry, measurable by inftltration rate, is thought to
provide about half (50o/o) of this function. Resisting degradation, measured
primarily by aggregate stability, is of second importance. Most of the
measurable indicators have been considered in previous chapters.
SoiI quality function Function weight Measurable indicator Indícator weigfu
1. Accommodate v/atel entry
2, Resist degradation
3. Facilitate water transfer and absorption
4, Sustain plant growth
50 Infiltration rate 50
35 Aggregate stability 27
Shear strength 4
Soil texture 2
Heat tíansfer capacity z
10 Hydraulic conductivity 5
Porosity 2
Macropores 3
5 Rooting depth 1
water relations z
Nutrient re]ations 1
Chemica] barriers 1
Modified from Karlen and Stott (1994).
874 Global Soíl Qualíty as Affected bg Human Actívítíes
TABLE 20.3 lmportance Assigned to Various Soil Functions in Ascertaining Soil Quality
in Different Times and circumstances
Note the very high weights for the food- and /iber-production function in 1900 worldwide,
and in clevelopíng countries toclay. Other functions concerned with environmental
and habitat issues are much more prominent today in industrialízed countries.
Probable Weights
Soil fúnctiott
worltlwide,
1 900
Industri ali zed countries,
2000
Deyeloping countries,
2000
1. Foocl and fiber production
2. Resistance to erosion
,]. \Vater and air quality
4. Food quality
5. Wildlife habitat
6. Construction and transport base
7o
10
5
5
5
5
85
1
,)
1
5
1
s
40
15
10
1t)
15
10
recognized. In developing countlies/ however, where hunger and even famine are still
common/ food and fiber production remains the soii-quality issue of prime importance,
as indicated by the high weight given to this function in Table 20.3.
\ J n a Q €m€nt-i ensítíue lndícator s
There is considerable variation in the degree to which soil management can promptly
alter properties that are indicators of soil quality. As shown in Figure 20.2; some properties
such as soil texture, mineraiogy, steepness of slope, and stoniness are inherent
characteristics of the soil and aíenot subject to change through land and crop management.
While these properties are important in determining the best management systems
to be used, they will not be changed by whatever system is chosen.
At the other extreme are plopelties that may be subject to almost daily control so
that their effect on soil quality is immediate. Examples are the soil water content as
affected by irrigation and rainfall, and the nutrient element levels that are subject to
prompt change as chemica1 fertilizers are applied. Also, the compaction of the soil can
result from passes across the field in one day by trucks and farm machinery. These properties
are likewise significant since they can influence the production of plant residues
upon which other more long-term properties are dependent.
Intermediate between these two extremes we find properties that are subject to
change only through long-term management efforts. Soil organic matter content and
active carbon levels, along with microbial biomass and soil aggregation, are examples of
this intermediate class of indicators of soil quality. It takes years of careful management
to raise the leve1 of these properties in soils, but once they are raised, they tend to
remain high for an extended period of time. These properties are highly desirable
because of their effects on dynamic soil processes such as \^/ater and air movement, soil
etosion, and the generation of biodiversity. But they can be developed only if we as soil
managers have at least a general understanding of the complex processes that generate
them.
Ephemeral
-l::nges within days or
r.lutinely managed
\\ ,:ter content
FieId soil respiration
'pH
. \1inera| N
. \raiiable K
. \raílable P
. BuIk density
lntermediate
Subject to management
over several years
. Aggregation
. Microbial bíomass
. Basal respiratíon
. Speciíic respiration
quotient
. Active C
. Organic matter content
permanent
lnherent to proíile
or site
. Soil depth
. Slope
. Clirnate
Restrictive layers
. Texture
. Stoníness
. Mineralogy
FIGURE 20.2 Classitication of soi1 properties contributing
to soi] quality based on their permanence
and sensitivity to manaSement. Some soil ploperties
ale quite ephemeral and change readily from day to
day as a result of routine management practices oI
lVeather. others are permanent properties inhelent to
the soi1 profile or site and are iittle-affected by management.
A management-oliented soil-quality assessment
would focus on properties that are intermediate,
but all propelties tend to be mutually reinforcing.
fFrom Islam and WeiI (2000)]
THr CorucrpT oF SolL QunLIry/SoIL HEALTH 875
202 soll REslsTANcE AND REslLlENcE3
Before turning to specific agroecosystems that affect soil quality, two other concepts
relating to soil quality should receive attention. First is soil resistance, or the capacity of
a soil to resist change when confronted with any kind of force or disturbance. For example,
the soil solution levels of potassium in some fine-textured soils high in hydrous
micas are not seriously affected by the removal of this element in harvested crops. The
potassium extracted from the soil solution by plant roots is quickly replenished from
exchangeable and nonexchangeable forms found in the clay and silt fractions of these
soils. In other words, the soil resists change, a characteristic not found in most sandy
soils that lack significant levels of exchangeable and nonexchangeable potassium. A
soil's capacity to resist change is an important component of soil quality.
A second important concept bearing on soil quality is that of. soil resilience, or the
capacity of a soil to rebound from changes stimulated by disturbances or external
forces. A soil under natural forest or grassland vegetation is disturbed when the land is
cleared for cultivation, and properties such as organic matter content, organic matter
quality, and aggregate stability all decline, thereby reducing soil quality, If, however, the
land is turned back to nature, or if other sustainable conservation systems of soil management
are utilized, the soil will begin to recovel and regain some of its lost properties.
The degree to which recovery takes place and its speed in doing so are measures of soil
resilience, a vital component of soil quality. Figure 20.3 illustrates how soil resistance
and soil resilience relate to soil quality through soil functions, and how they can affect
soil functions on t\^/o soils that vary in thek capacity to resist and recover.
Factors Affectíng 5oílResísúanceand Resílíence
Soil resistance and resilience are affected by both inherited and dynamic or managementoriented
characteristics. For example, inherited characteristics such as texture, type of
clay minerals, slope, and climate largely determine soil resistance, and have significant
3For a recent discussion of these two concepts see Seybold, et al. (1999).
FIGURE 20,3 (Upper)The concept of how soil resistance and soil
resilience relate to soil quality through soil functions. Resistance
acts a5 a buffer in slowing down change stimu]ated by a disturbance,
while resilience mechanisms help the soil recover from the
negative effects of the disturbance. (Lower) The effect of a disturbance
such as compaction on the functionin8 capacity of two
soils differing in their lesistance and resilience. The first soil, vrith
low resistance to change, functions very poorly after the disturbance.
In contlast, the disturbance only modestly affects the
function of the second soil with its high resistance. Fortunatel,
the first soil has high resilience, so in a matter of time, its function
Iecoveís to the orisinal level. Resistance assured the second soil's
function in spite of the disturbance, while resilience brought the
first soil back up to it's original function level. [Upper modified
from Seybold, et al. (1999); used with permission of Lippincott,
Williams, and Wilkins, Baltimorel
:]>. ]a
i,ii,,, ,.,
,,§:,],t,lóo
,9., ]]],,.]
,q]]]] ]] ]]
\o
ó.:l],l, ,]:.,
)a,:.:::: :
]o': ]
Soil with
876 Global Soíl Qualíty as Affected by Human Actíoítíes
effects on soil resilience. Dynamic properties such as those associated \^/ith the type of
vegetation, nutrient cycling, water and land management, as well as the underground
community of organisms, play a vital role, especially for soil resilience. For example,
properly managed cropland systems can not only increase the amount and quality of
soil organic matter in a degraded soil, but can speed up the rate of organic matter
buildup. In other words, these systems can enhance soil resilience, an important component
of soil quality. The significance of both soil resistance and soi] resilience will be
seen later on as \^/e focus on more specific ecosystems that are affecting soil quatity.
We now turn to the three primary functions of soils that must be performed if soit
quality is to be considered satisfactory. Our initiai focus will be on biological productiv_
ity, since all iife is dependent on it. However, the other two functions-maintaining
environmental quality and enhancing human and animal health-will also receive
attention, particularly as they are influenced by the attempts of humans to maximize
biological productivity.
]CI.3 §tl§TAlT\lN6 EIOLOGlcAL pRoEueT§VlTY
No other soil function affects all living cleatures more than does the sustenance of biological
productiviý. Human survival through the ages has depended on this function,
and wili likely continue to do so. Likewise, the survival of countless numbers of soil
organisms is dependent on the soil's capacity to support biological productivity. We
turn our attention to satisfying human needs for food and fiber, since the survival of
other organisms is often determined by how we satisfy these human needs. We witl
review the world's food production problems, how they have been coped with, and how
soil quality has benefitted and suffered from the actions we have taken.
The Fírst í0,00CI Vears
Since the dawn of agriculture some 10,000 years ago/ people have cleared forests and
prairies so that the land could be used to grow food and fiber for their growing families.
Initialiy, because there was an abundance of land and relatively few people, the change
from the more sustainable natural vegetation to the less stable agricultural systems had
only local effects on soil quality.
As humans became more numerous, soil productivity suffered over wider areas.
Examples include the salinization of the once very productive irrigated lands of ancient
Mesopotamia in the Middle East (see Section 10.3) and the severe water erosion of hilly
lands upon which the Greeks and Romans depended for food (see Figure L7 .24). These
peoples turned to less densely settled lands in North Africa and Europe for the produc_
tion of food. Consequently, the degradation of soil quality in these early periods had
only modest global effects.
As human populations increased further and the productivity of farmed soils faltered,
food production was increased primarily by expanding the area of land under
cultivation, not by increasing yields per hectare. This was particularly true after the
Europeans "discovered" the Western Hemisphere, whose virgin soils soon produced
food not only for the local inhabitants, but for expolt to the food-deficient parts of
the globe.
Pcsů §-#míf eernfrarry
It is only in the past half century that pressures on land for crop production have
become so acute, forcing people to consider alternatives to expansion of cultivated land
as means of meeting human needs for food and fiber.a This change stems both from the
unprecedented increases in the numbers of people to be fed, and from those people's
enhanced ability to purchase food and fiber that others produce. We will start with the
population explosion.
a
Human demands for fiber that is used to manufacture cloth, paper, 1umber, rope, machinery coveís/
and so forth also grow with human population numbers. Plants such as cotton, hemp, and trees are used
to help meet these demands. While our major focus wi1l be on expanding food needs, demands for fiber
also íncrease.
Sus-rnpiottnio Btoroelcnr Fxcruťíll.,nry Fr?7
Population projections by region Relative urban and rural population
0
€
5
tr
o
6
o_
o
ól
1.5
l 1.0
l0,5
l0.0
9.5
9.0
8.5
8.0
7.5
7.o
6.5
6.0
5.5
5.0
4.5
4.o
3.5
3.0
).5
2.0
1.5
1.0
.5
o
l 95o 2o00
Year
)0)5
Fl6URE 20.4 From the beginning of the human race until 1960, the wor]d's population increased to about 3 billion. Less than 40 n-_ _
yeaís wele needed to provide the second 3 billion. The total is expected to íise to 8.5 billion by the year 2025. (,Left) Note that esseni_:
all the growth is in the lower-income developing countries and regions that are already pressed to provide food for their growing pc: _
]ations. Also note (right) the increasing proportion of the developing countly populations that live in urban areas. While consider":-.
quantities of vegetables and other food crops are glol\rn in or around the cities, most of the food required for the urbanites must be :
duced out in the rural areas. Also, urban 1iving provides little opportunit;, for family and community sharing, commonly found in nl,:
rurai areas. fSources: (IeP UNFPA (1992); (Right) United Nations (1996)]
2a.4 THE PoPuLATloN EXPLosloN
[,T.N. |oocl and Agriculirrre
Orgartiza titlrr (Fl\(l ) :
WWW.Íao.org,'
Modern medical advances following World War Ii stimulated unparalleled increases .:
human populations and in demands for food (Figure 20.4). These demands Ývere met ],.
farmers who produced more food in the past half century than had been produced
the previous 10,000 years of the history of agriculture.
TAB|_E ]0"4 Percent of lncrease in Food Production
in Diíferent Regions Between l96l to l963 and
l 989 to l 990 Attributable to lncreases in Area
Cropped and to lncreases in Yields Per Hectare
I ncr e as e attributab le to
Regioll
Increased
area, o/o
Increased
yields,^ o/o
Low-income countlies
Sub-Saharan Africa
Latin America
Middle East/North Africa
South Asia
East Asia
High-income countrles
World
47
30
aa
1,4
6
z
8
52
77
77
B6
94
9B
92
" Includes both increasing the number of crops pel year and increased
yields per hectare.
Data from the Food and Agriculture Organization (FAO).
878 Global Soíl QualítE as Affected bg Human Aetiuítíes
;Ll-:3
To achieve this target, it was necessary either (1) to clear and cultivate native
forests or water-deficient grasslands, much of which were ill-suited for cultivation;
or (2) to greatly increase the cropping intensity and the yields per hectare on the
more Productive lands already under cultivation. Both sources of enhanced food
Production were utilized, but most of the needed food came from increased production
on existing farmlands (Table 20.4). As we shall see, both of these approáches to
increased food production resulted in serious consequences for the qúáIity of the
world's soils.
§ trNTEN §fi F! En A6 RoEco§Y§TEM §-TF-|E G REtN REVOLL|T§cN
When the human population explosion became evident after World War II, many
experts predicated widespread starvation. Their predictions were based primarily on the
assumption that, as in the past, expansion of cultivated land would be the primary
means of increasing fcrod production. They ignored possibilities for increased production
intensity on land already in cultivation, and they were wrong.
Scientists and their farmer collaborators developed and put to use intensified soil-,
\^r'ater-, and crop-management Systems that 8ave unparalleled increases in food production,
especially in the developing countries of Asia and Latin America, Food production
increased more rapidly than population in all major regions except sub-Saháran Africa
(Figure 20.5). Grain halvests nearly tripled worldwide from 1950 to 1990. As a result,
the threat of massive starvation was averted, and the cost of foods (primarily cereals)
actually fell. Lowered food prices benefitted poor people everywhere, in cities as well as
rural areas.
The vastly increased production resulted from farming systems that integrated
newly created high-yielding cereal varieties (wheat, corn, and rice) with increased water
availability through irrigation and dramatic increases in nutrient inputs from chemical
fertilizers (Figure 20.6). Monoculture systems were intensively used, and two or three
crops \^/ere harvested annually.
More than 7Oo/o of the increase came from intensified farming, the remainder from
increases in cultivated land area. The results \^/ere most spectacular in Asia and Latin
America, where the term green revolution was used to describe the process. Wheat yields
in India, for example, increased by nearly 4OOo/o fuom 1960 to 1985, and yields of rice in
Indonesia and China more than doubled. The global caloric intake increased to about
2700 kilocalories, about 760/o above minimum needs. Although millions still remained
hungry, human nutrition among the poor was greatly enhanced since the real cost of
these cereals declined by about 7 Soh, makíng them more easily available to low-income
citizens.
Food production per per§on, l 96 l : l00
a
-'?
.I,
Asía (developing)rr- -''
.-' World
--| *,;ť"w"**o*****-- --2
--",e--:'-, *
3{_^z:.i
' Latin America and Caribbean
,,., ,* _r\_* _
c._La-l,____ A1, * § *"
Sub-§aharan Afríca* *+ý
F|GURE 20.5 Changes in pel capita food production in
different regions of the world between 1961 and 1995, Food
production pel person worldwide increased neaiy 2}o/o,
but in the develóping countries of Asia, the increáse was
nearly 7oo/o. Only in sub-Saharan Africa (exctuding South
Africa) did the per capita food production decline. Most of
the increases resulted from agricultural intensification,
fData from FAO]
!Nrtruslrtrp AcnorcosysTEMs-THE GRprru Rrvoiurtoru 879
,
F|GURE 20.6 Increases in fertilizer use in industrial l:]r]
developing countries and in world irrlgated area since ] ý:,Note
the 2S-fotd increase in fertilizěr use in der-elc:_:rg
countlies and the worldwide doubling of land under ir_-,:;
tion- The drop in industrialized couni.y fertiiizer use §J.1
1990 is due primarily to decreases in the states of the tbr=,<:
Soviet Union, although use in the United States and Lu::rrt
has ]eveled otT, (From FAO data and author's calculatio:l.
20.6 EFFECT§ oF lNTENslFlED AGRoEcosYsTEMs oN soll QUAL|TY oR HEALTH
Few quantitative studies have been made of the effect of production intensification c,:
::i'rTi$]''
But indirect evidence su8gests that both posiiive and negative effectshal-=
PosítíueEffects
On the Positive side, intensified agriculture has generally maintained or even increascthe level of some macronutrientiin soil, since řhese elÓments are commonly supplie;
from outside SouICeS/ such as manufes/ lime, or fertilizers. Where appropriate modťfapplications of chemical fertilizers have been used/ the N, p, and x cbmp'onents or i'.quality have often been enhanced.
Intensified agriculture has also increased the level of plant production, permitting icorresPonding increase in the amount of crop residues t'hat can be returned to the soj_,
Su.ch residues Provide soil cover, reduce soil Órosion, and can help maintain or increa-soil organic matter levels (Table 20.5). Soil quality is thus páiitl"6ry affected if ; ř;;;;.amount of crop residues is returned to the soil.
, A third and likelY even more significant positive effect of intensification is its ten_
dencY to reduce Pressures on fragiř lands tÉatmight otnerwise rrave been cleared ancCultivated to Produce the additilonal food needeČ. Agriculture has been intensifiec
mosjlY,on*the more Productive,,relatively level soils, *i".. risks from erosion are no:too high, BY Producin8 most of the additional food on trrese solis, the need ro.
""pu.rá_1"q,o"l9_
more fragile lands has been minimized. Figure zo.z ttlusttates this point fo:India, Were it not for the wheat yield gains from t]he gr..r. i"rot,rtion, the countn-would have been force_d to plow an addiřional 42 millioň ha of fragile Ú.ior, il"rilr',.for,ests, an area equivalent in size to the state of California. Wo.ldi,iil;;-á.!ir."řŽo".million ha-equal to the area of the great Amazon basin-have been ,,saved,,
due to
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880 GIobaI SoíI Qualíty as Affected by Human Actíuíties
TAE§_E 2ú.5 The Effect of Nearly 30 Years of Continuous Rice Cropping
(3 Crops per Year) with and without Nitrogen Fertilizer on the Organíc
Carbon and Total Nitrogen in a §oil in the Philippines
Note the higher organic carbon and N leyels in the soil tcl which heavy
applications of nitrogen (330 kg,ha/yr) were applied. Phosphorus
and potassium were applied to all plots.
Organic carbon in soil, g/kg Total N in soil, g/kg
NtlN
applied
330 Kg N,4la/yr
applied
NoN
applied
330 Kg N/ha/yr
applied
1963
l978
19B3
19B5
I99l
I992
1B.3
18.B
18.7
20.4
20.4
20.7
18.3
21.4
21.4
23.9
,2 (
23.0
7.94
1,.97
1.95
2.07
7.97
2.o9
1,.94
2.22
2.14
2.38
Z.27
2.30
Moditied from Cassman, eí al. (7997).
increased yields of all cereal crops. It is almost celtain that the quality of soils would
have declined significantly on the forest and prairie lands that would have been
brought into cultivation had crop intensification not been used.
Another possible aspect of the green revolution is the increased efficiency of nutrient
use by some of the improved cereal varieties (Figure 20.8). For example, when 75 kg
N/ha was applied to the traditional wheat varieties of 1950, only 45 kg of wheat was
produced for each kiiogram of nitrogen added. Improved varieties of the mid_1980s
produced 70 kg of wheat per kilogram of added nitrogen. Note, however, the lower efficiencies
of all varieties when high nitrogen rates are used.
250
l00
7) 75 78 81 84 87 90 93
FiGilRE 20.7 (Left) In the 1990s, if India had been forced to produce its ,\^/heat
with technologies and varieties of the 1960s, farmers
r,r'ould have needed about 40 million more hectares of farmland. Most of this extra farmland would have to come from easily erodible
forest]ancis that ale characterized by steep slopes. (Rrgrr) The increase in giobal per-hectare yields of cereai crops (wheat, corn, and rice)
from 1970 to 7994 il7as associated n/ith a reduction in the world food price index for these foods, meaning that consumers paid less for
them. The poor people in developing countlies (urban as well as rural) wele the gíeatest beneficiaries of these reductions. [Right from
CIMMYT (1995); 1eft írom The Econtlmist, June 10, 1995l
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Food
índex
š š
1970 7) 14 76 78 80 82 84 86 88 90 92 94
Errrers or lNTENsIFIED AcRoEťo§ysTEM§ oN §olt Qunllry oR !-!EAITH 8E]_
10
60
z50oo
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20
Io
Negatíue Effects
'I-echnicai notes on the statc
r lI i hc tt,tlir ttl'r (.C(,\\ \lqIn\,
crclplallds, anc1 soi1 nutricnt
] el,el s:
WWW. us-ecosystems.org
l 950 l 960 l 962 l 966 l97o 1973 1979
kgN/ha ffi75N Dl50N n3O0N
Fl6URE 20.8 The efficiency of nitrogen utilization of traditional wheat cultivars of 1950 compal.:
v/ith that of the steadily improved cultivars that have since been used in intensified agriculture in der-..oping
countíies. At a11 fertilizer nitrogen application rates, the improved cultivars ale mole efficient th::the
traditional varieties of 1950. Note, however, that nitrogen use efficiency is much lower at the high.:
rates (150 and 300 kg N/ha) than at the moíe modest rate of 75 kg N/ha. [From CGIAR (1997)]
Intensive agíiculture also has had negative effects on the quality of some soils. Tl.
application of chemical fertilizers generally provides ample quantities of nitroge:
phosphorus, and, in some cases/ potassium.5 However, the removal of other nutrients _:_
the bumper crops often results in micronutrient deficiencies. Also, in some cases the o\_dation
of nitrogen added in fertilizers results in increased soil acidity. Both effects cou.:
lower soil quality.
Excess Nurtl,irrurs" ln many areas of the world, such as East Asia and Western Europe (F_.ure
20.9) such nutrients as nitrogen and phosphorus were added in quantities far ,:.
excess of plant uptake. With time, the levels of these nutrients built up in the soil, a::
they moved as pollutants into the runoff or drainage y/atels or into the atmosphele, S...
quality is said to be reduced, since products moving from the soil adversely affect en,,,.IonmentaI
quality.
§ellnlznrtoru. Irrigation-induced salinization is another negative effect of agricultul..
intensification on soil quality. For example/ each year the salt added in irrigation wa:e:
to the soils of Atizona is equivalent to about 350 kg for each of the 4 million people 1,, ing
in the state. Worldwide, some 30olo of irrigated soils are significantly affected :salinizationt
some so seriously that the iand has been abandoned.
Fpsrlclors. Chemical pesticides that are commonly used in intensified agriculture s-, items
can adversely affect soil quality. While some olganochemicals adversely affec: ,
broad spectrum of soil organisms, others are selective, reducing biological divers_:"
more than overall abundance. Some soils treated decades ago with high levels _
arsenic- or copper-containing insecticides still have toxic levels of these chemica_,
Because of the uncertain effects of today's pesticides on soil quality, integrated pest ttt,;.,--
agement systems that minimize the use of these chemicals should be emphasized,
5
When cleared 1ands are cultivated, deficiencies of nitrogen and phosphorus aTe fiíst to appear, and :.:tilizers
are applied to meet these needs. However, crop removals soon 1owet the potassium levels of sc: .
soils, especially those that are highly weathered and low in 2:l-type clays, such as i]lite.
882 Gtobal §oíl Quolífg os ,Aífeeíedbry F,§airt,lol,r Aeťí$íťíes
I
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East Asia
South Asia
Latin America
Sub-§aharan Aírica
Eurasia
North America
Western Europe
Developing countrie§
Developed countrie§
World
FIGURE 20.9 Rates of fertilizer nutlient use in selected
regions of the v/oíld in 1995. Note the very high use in East
Asia, where multiple cropping is Common, and in Western
Europe, where highly intensive agriculture is practiced. In
both regions some excessive-use sites have been identified.
Also note the very low rates in sub-Saharan Africa and in
Eurasia (the newly independent states of the former Soviet
Union), where plant production is constrained by nutíient
deficiencies. Ferti]izer use in the united states is about average
for the world. While there are some high-use systems in
irrigated and humid areas, these are balanced by the very
low rates in vast areas of dryland farming where water,
ratheI than nutrient deficiencies, is the first limiting factor.
[Data from FAO published in Bumb and Baanante (1996)]
50 200
HrnrrHy Dlrr. Intensive agricultural systems have focused primarily on cereal crops/
such as wheat, corn, and rice, which provide about ha]f the world's calories and are
quite responsive to external inputs, such as water and fertilizers. Unfortunately, less
attention has been paid to the pulses (beans, peas, and lentils), fruits, and vegetables. As
a lesult, the area planted to these Crops actually decreased in some countíies. For example,
in India, the area of land devoted to pulses decreased by l3o/o from 1970 to 1995.
This has implications for human health because/ compared to the cereals/ the pulses are
generally higher in proteins and micronutrients, and leafy vegetables are higher in vitamins.
Human diseases associated with deflciencies of micronutrienfs, such as iron and
zinc, and with vitamin A, are widespread in tropical countries. AIso, the pulse legume
residues provide some organic nitrogen that is leleased slowly for subsequent crop
uptake. Exclusive emphasis on celeals has thus indeed reduced soil quality in many
countries of the world.
Frnnr Dtsp4sr. Similarly, the green revolution has had some negative impacts on soil
quality because the improved cereals have commonly been glo\ďn in monoculture season
aftel season. In some areas/ research has sho,//n a decline in the biological productivity
of monoculture systems. This may be due to the buildup of pathogens or of allelochemicals
that are toxic to the crop, or to declining levels of micronutrients in the soil. In any
case/ when cropping systems do not take advantage of the benefits of crop rotation, soil
health or quality declines accordingly,
Rroucro Bloolvrnslry. High input, intensified agriculture using monoculture systems generally
adversely affects biodiversity. For example, before intensification of agriculture in
China, farmers were growing 10,000 varieties of wheat. Today that number is 1000 or
less. Furthermore, the bulk of the wheat is being produced by a much smaller number of
high yielding varities. Intensified systems also significantly affect the abundance and
biodiversity of soil organisms. Monoculture systems provide little diversity in the
organic residues and in the associated organisms that take part in their decay. We know
that the clearing and cultivation of forested lands reduces the numbel of fungi and
increases the relative numbers of bacteria (see Section 1 1 . 1 5). The ratio of fungal biomass
to that of bacteria may be about 1:1 in cultivated soils, about 3:1 in minimum tillage
areas, and more than 100:1 in forested areas. Monoculture systems/ especially those
where the crop residues are removed or burned, also reduce the number of earthy/orms
and other macroorganisms, compared to their numbers in systems with crop rotation.
Effects of intensification on the biodiversity among species of bacteria is somewhat
less certain because their extremely small size makes it difficult to measure their diversity.
However, the advent of new molecular biological tools that provide DNA analyses
has already shoy/n the close interaction of numerous microbes in soils and has indicated
that this interaction is modified as soil and plant environments change.
l0o I50
Kilograms/hectare
3
Erprcrs oF lNTENslFlED AGRoEcosysTEMs oN SolL Ounltry oR HEALTH 8B3
Anímal Feedlots
In Section 16.5 we discussed what intensified animal production systems can do to soil
quality, While these systems are efficient in terms of feed conversion to animal protein,
they have adverse effects on soil quality and health. They remove plant products from
wide areas and concentrate them into a production factory, the wastes from which
often pollute the surrounding soil and v/ater systems with nitrogen, phosphorus, and
pathogens. Soil quality is most certainly affected negatively by such intensification.