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This paper describes the agroecological principles necessary to guide the conversion of high‐input conventional systems to a low‐input management based on crop diversification and livestook integration schemes which break the monoculture nature of conventional systems. The new crop‐crop and crop‐animal combinations result in a series of synergisms and complementarities among farming system components which lead to optimal recycling of organic matter and nutrients, and to balanced pest‐natural enemy populations. Thus, agroecological design goes beyond “input‐substitution” by establishing systems capable of sponsoring their own soil fertility, crop protection and yield constancy. These new agroecosystems provide a sustainable level of productivity with minimal need for external (conventional or organic) resources. Biological structuring sponsors the functioning of the system.
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International Journal of Environmental Studies
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Agroecology and the conversion of lárgescale
conventional systems to sustainable management
Miguel A. Altieri & Peter Rosset
To cite this article: Miguel A. Altieri & Peter Rosset (1996) Agroecology and the conversion
of lárge‐scale conventional systems to sustainable management, International Journal of
Environmental Studies, 50:3-4, 165-185, DOI: 10.1080/00207239608711055
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Intern. J. Environmental Studies, 1996, Vol. 50, pp. 165-185 © 1996 OPA (Overseas Publishers Association)
Reprints available directly from the publisher Amsterdam B.V. Published in The Netherlands
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Printed in Malaysia
AGROECOLOGY AND THE CONVERSION OF
LARGE-SCALE CONVENTIONAL SYSTEMS TO
SUSTAINABLE MANAGEMENT
MIGUEL A. ALTIERI* and PETER ROSSET
(Received in Final Form: August 4, 1995)
This paper describes the agroecological principles necessary to guide the conversion of high-input conventional
systems to a low-input management based on crop diversification and livestook integration schemes which
break the monoculture nature of conventional systems. The new crop-crop and crop-animal combinations result
in a series of synergisms and complementarities among farming system components which lead to optimal
recycling of organic matter and nutrients, and to balanced pest-natural enemy populations. Thus,
agroecological design goes beyond "input-substitution" by establishing systems capable of sponsoring their
own soil fertility, crop protection and yield constancy. These new agroecosystems provide a sustainable level
of productivity with minimal need for external (conventional or organic) resources. Biological structuring
sponsors the functioning of the system.
KEYWORDS: Agroecology, sustainability, synergism, ecological turntable, cover cropping, crop-livestock
integration.
INTRODUCTION
Most scientists today would agree that conventional modern agriculture faces an
environmental crisis. Land degradation, salinization, pesticide pollution of soil, water
and food chains, depletion of ground water, genetic homogeneity and associated
vulnerability, all raise serious questions regarding the sustainability of modern
agriculture.1 In the Third World, this crisis is becoming understood as a crisis of a
development path which proved misleading in guiding agricultural betterment. The end
result has been a vicious cycle of rural poverty and environmental degradation. In the
industrialized world, the problem is beginning to be seen as manifestations of a sort of
"technological saturation" associated with the intensification of production dependent on
agrochemicals and fossil energy. The very nature of the agricultural structure and
prevalent policies have lead to this environmental crisis affecting modern agriculture by
favoring large farm size, specialized production, crop monocultures and mechanization.
As farmers are integrated into international economies, imperatives to diversify
disappear as monocultures are rewarded by economies of scale. In turn, lack of rotation
and diversification take away self-regulating mechanisms, turning monocultures into
highly vulnerable agroecosystems dependent on high chemical inputs.
The causes of the environmental crisis are thus rooted in a prevalent socioeconomic
system which promotes monocultures and the use of high input technologies and
* Department of Environmental Science, Policy and Management University of California, Berkeley,
California (U.S.A.)
Institute for Food and Development Policy, Oakland, California (U.S.A.)
165
166 M. A. ALTIERI AND P. ROSSET
agricultural practices that lead to natural resource degradation. Such degradation is not
only an ecological process, but also a social and political-economic process. This is why
the problem of agricultural production cannot be regarded only as a technological one,
but while agreeing that productivity issues represent part of the problem, attention to
social, cultural and economic issues that account for the crisis is crucial.
The loss of yields due to pests in many crops, despite the substantial increase in the
use of pesticides is a symptom of the environmental crisis affecting agriculture. It is well
known that cultivated plants grown in genetically homogenous monocultures do not
possess the necessary ecological defense mechanisms to tolerate the impact of out
breaking pest populations. Modern agriculturists have selected crops for high yields and
high palatability, making them more susceptible to pests by sacrificing natural resistance
for productivity. On the other hand, modern agricultural practices negatively affect pest
natural enemies, which in turn do not find the necessary environmental resources and
opportunities in monocultures to effectively and biologically suppress pests.4 Thus while
the structure of the monoculture is maintained as the structural base of agricultural
systems, pest problems will continue to be the result of a negative treadmill that
reinforces itself (Figure 1).
The concept of sustainable agriculture is a relatively recent response to the decline in
the quality of the natural resource base associated with modern agriculture. Today, the
question of agricultural production has evolved from a purely technical one to a more
complex one characterized by social, cultural, political and economic dimensions. The
concept of sustainability although controversial and diffuse due to existing conflicting
definitions and interpretations of its meaning, is useful because it captures a set of
concerns about agriculture which is conceived as the result of the co-evolution of
socioeconomic and natural systems.5 A wider understanding of the agricultural context
requires the study between agriculture, the global environment and social systems given
that agricultural development results from the complex interaction of a multitude of
factors. It is through this deeper understanding of the ecology of agricultural systems that
doors will open to new management options more in tune with the objectives of a truly
sustainable agriculture.
This concept has prompted much discussion and has promoted the need to propose
major adjustments in conventional agriculture to make it environmentally, socially and
economically viable and compatible. Several possible solutions to the environmental
problems created by capital and technology intensive farming systems have been
proposed and research is currently in progress to evaluate alternative systems. The main
focus is on the reduction or elimination of agrochemical inputs through changes in
management to assure adequate plant nutrition and plant protection through organic
nutrient sources and integrated pest management, respectively. Agroecology's idea is to
go beyond the use of alternative practices and to develop agroecosystems with minimal
dependence on high agrochemical and energy inputs, emphasizing complex agricultural
systems in which ecological interactions and synergisms between biological components
provide the mechanisms for the systems to sponsor their own soil fertility, productivity
and crop protection.6
Although hundreds of more environmentally prone research projects and
technological development attempts have taken place, and many lessons have been
learned, the thrust is still highly technological, emphasizing the suppression of limiting
factors or the symptoms that mask an ill producing agroecosystem. The prevalent
philosophy is that pests, nutrient deficiencies or other factors are the cause of low
productivity, as opposed to the view that pests or nutrients only become limiting if
conditions in the agroecosystem are not in equilibrium. Thus today the main emphasis is
on the biotechnological development of transgenetic varieties resistant to stress factors,
SUSTAINABLE AGROECOLOGY
167
MONOCULTURE
NATURAL VEGETATION
DISPLACEMENTINTENSIVE
USE
OF FERTILIZERSINTENSIVE
USE
OF PESTICIDES
_L
MASSIVE
SUPPLY
OF
HOST PLANTS
HOST PLANT
SWITCH
RECRUITMENT
OF HERBIVORES
J_
DESTRUCTION
OF
BENEFICIAL
HABITAT FAUNA
_L
REDUCTION
IN BIODIVERSITY
DISRUPTION
OF
NATURAL CONTROL
IN SITU COMPLETION
OF LIFE CYCLES
NUTRITIONAL
IMBALANCE
IN CROPS
HIGHER
VULNERABILITY
TO PESTS
HERBICIDESINSECTICIDES
RESISTANCE
TO
INSECTICIDES
ELIMINATION
OF
TRAP CROPS
AND
INSECTARY PLANTS
HARBORING
NATURAL ENEMIES
ELIMINATION
OF
NATURAL
ENEMIES
PEST
RESURGANCE
MORE SEVERE PEST PROBLEMSSECONDARY
PESTS
TREADMILL EFFECT
Lower effectiveness
of
Insecticides
Higher use
of
insecticides
Higher costs
of
production
Yield decline
in the
long term
FIGURE 1 The ecological consequences of monoculture with special reference to pest problems and the
agrochemical treadmill.
and
on the
other
on
organic agriculture, focusing
on an
input substitution approach aimed
at replacing costly
and
degrading agrochemical
and
high-input technologies
for
more
environmentally sound, low-external input technologies. These approaches
do not
address, however,
the
ecological causes
of the
environmental problems
in
modern
agriculture which
are
deeply rooted
in the
monoculture structure prevalent
in
large scale
production systems. There still prevails
a
narrow view that specific causes affect
productivity,
and
overcoming
the
limiting factor
via new
technologies, continues
to be
the main goal. This view
has
diverted agriculturists from realizing that limiting factors
only represent symptoms
of a
more systemic disease inherent
to
unbalances within
the
agroecosystem
and
from
an
appreciation
of
the context
and
complexity
of
agroecological
processes thus underestimating
the
root causes
of
agricultural limitations.7
Today,
the
problem
of
increasing food security while conserving
the
resource base
requires
not
only profound changes
in
strategic research agendas,
but
also
on the
168
M. A.
ALTIERI
AND P.
ROSSET
fundamental approaches
to
rural development that involve true farmers participation.
Although
the
challenge
for
sustainable production affects
all
regions
in the
world, their
intensity
or
perceived importance differs
in
each area depending
on
whether systems
are
large
or
small scale, subsistence
or
market oriented,
etc.
Clearly
in the
commercial
sectors
of
agriculture, profit motivation, rather than environmental concerns have guided
agricultural development,
and the
resulting environmental
and
social consequences
of
such direction
are now
starting
to be
assessed.
In the
small farm sector, historically
speaking, "development"
has not
reached
the
vast population
of
resource-poor farmers.
Therefore, there
is a
great need
to
match
an
appropriate agricultural development
approach with
the
needs
of
this sector
of
society.
In both cases,
the
development
of an
"appropriate technology" capable
of
translating
productive potentials into sustainable livelihood
for all has
been
a
central idea.
A
number
of agricultural research
and
development schemes
(i.e.
farming systems research
and
extension, agroecosystem analysis
and
development,
etc.)
have been suggested
in
order
to reach this goal. Most
of
these approaches:
(1)
emphasize
a
systems framework
of
analysis;
(2)
focus
on
both biophysical
and
socioeconomic constraints
on
production;
(3)
utilize
the
agroecosystem
or
region
as a
unit
of
analysis. These approaches have
improved diagnostic methodologies
and
have also introduced
new
criteria
(i.e.
sustainability, equitability, stability,
etc.) to
evaluate
the
performance
of
agricultural
systems.2
In addition, these
new
approaches have allowed
us to
better understand,
in a
more
fully integrated manner,
the
various factors that govern agricultural productivity
and
have allowed
the
development
of new
technological avenues
to
overcome these factors
in
a
more environmentally sound manner. However,
by
perceiving
the
problem
of
sustainability solely
as a
technological problem
of
production, most agroecological
approaches
are
restricted
in
their ability
to
understand
and
address
the
fundamental
reasons
why
agricultural systems become nonsustainable. Clearly,
new
sustainable
agroecosystems cannot
be
implemented without modifying
the
socioeconomic-economic
determinants that govern what
is
produced,
how it is
produced,
and for
whom
it is
produced. Agroecology should deal with technologial issues
in
such
a way
that these
assume their corresponding roles within
a
political agenda that incorporates social
and
economic issues
in its
development strategy. Only policies
and
actions derived from
the
implementation
of
such
a
strategy
can
confront
the
structural
and
economic factors that
determine
the
agricultural-environmental crisis prevailing throughout
the
many regions
of
the
world.8
TOWARDS
AN
AGROECOLOGICAL STRATEGY
In
the
search
to
reinstate more ecological rationale into agricultural production, scientists
and developers have disregarded
a key
point
in the
development
of a
more self-sufficient
and sustaining agriculture:
a
deep understanding
of the
nature
of
agroecosystems
and the
soil degradation,
etc. is
understood
as
imbalance, then
the
goal
of the
agroecological
treatment
is to
recover balance:
the
agroecosystem's natural tendency toward repairing
itself.
This tendency
is
known
in
ecology
as
homeostasis,
the
maintenance
of the
system's internal functions
and
defense
to
compensate
for
external stress factors.
In
agroecology, biodiversification
is the
primary technique
to
evoke homeostasis,
self-
regulation
and
sustainability.
However, ecological health
is not the
only goal
of
agroecology.
In
fact, sustainability
is
not
possible without preserving
the
cultural diversity that nurtures local agriculture.
A
closer look
at
ethnoscience
(the
knowledge system
of an
ethnic group that
has
originated
SUSTAINABLE AGROECOLOGY 169
locally and naturally) has revealed that local people's knowledge about the environment,
vegetation, animals, and soils can be very detailed. Peasant knowledge about ecosystems
usually results in multidimensional land-use productive strategies, which generate,
within certain ecological and technical limits, the food self-sufficiency of communities in
particular regions. For agroecologists there are several aspects of traditional knowledge
systems that are relevant: knowledge of farming practices and the physical environment,
biological folk taxonomic systems, use of low-input technologies, etc. By understanding
ecological features of traditional agriculture, such as the ability to bear risk, production
efficiencies of symbiotic crop mixtures, recycling of materials, reliance on local
resources and germplasm, exploitation of full range of micro-environments, etc., it is
possible to obtain important information that may be used for developing appropriate
agricultural strategies tailored to the needs, preferences and resource base of specific
farmer groups and regional agroecosystems.
Stable production can only take place within the context of a social organization that
protects the integrity of natural resources and nurtures the harmonious interaction of
principles by which they function. Given this limitation, agroecology has emerged as the
discipline that provides the basic ecological principles for how to study, design and
manage agroecosystems that are both productive and natural resource conserving, and
that are also culturally sensitive, socially just and economically viable.6
Agroecology goes beyond a one-dimensional view of agroecosystems—their genetics,
agronomy, edaphology, and so on,—to embrace an understanding of ecological and
social levels of co-evolution, structure and function. Instead of focusing on one particular
component of the agroecosystem, agroecology emphasizes the interrelatedness of all
agroecosystem components and the complex dynamics of ecological processes.9
Agroecology also encourages researchers to tap into farmers' knowledge and skills and
to identify the unlimited potential of assembling biodiversity to create beneficial
synergisms that provide agroecosystems with the ability to remain or return to an innate
state of natural stability.
Sustainable yield in the agroecosystem derives from the proper balance of crops, soils,
nutrients, sunlight, mositure and other coexisting organisms. The agroecosystem is
productive and healthy when this balance and rich growing condition prevails, and when
crop plants remain resilient to tolerate stress and adversity. Occasional disturbances can
be overcome by vigorous agroecosystems which are adaptable and diverse enough to
recover once the stress has passed. Occasionally, strong measures (i.e. botanical
insecticides, alternative fertilizers, etc.) may need to be applied by farmers employing
alternative methods to control specific pests or soil problems. Agroecology provides the
guidelines to carefully do so without unnecessary or irreparable damage. Simultaneous
with the struggle to fight pest, disease or soil deficiency, the agroecologist strives to
restore the resiliency and strength of the agroecosystem. Agroecology provides the
methodological tools for community participation to become the driving force defining
the objectives and activities of development projects. The goal is for fanners to become
the architects and actors of their own development.
MANAGEMENT CONSIDERATIONS
From a management perspective, the agroecological objective is to provide a balanced
environment, sustained yields, biologically mediated soil fertility and natural pest
regulation through the design of diversified agroecosystems and the use of low-input
technologies. The strategy is based on ecological principles that lead management to
170 M. A. ALTIERI AND P. ROSSET
optimal recycling of nutrients and organic matter turnover, closed energy flows, water
and soil conservation and balanced pest-natural enemy populations. The strategy exploits
the complementarities and synergisms that result from the various combinations of crops,
trees and animals in spatial and temporal arrangements.5
In essence, the optimal behavior of agroecosystems depends on the level of
interactions between the various biotic and abiotic components. By assembling a
functional biodiversity it is possible to initiate synergisms which subsidize
agroecosystem processes by providing ecological services such as the activation of soil
biology, the recycling of nutrients, the enhancement of beneficial arthropods and
antagonists, and so on. Today there is a diverse selection of practices and technologies
available, and which vary in effectiveness as well as in strategic value (Table I). Some,
which include practices already part of conventional growing (genetic improvement,
minimum tillage, etc.) are of prophylactic value, while others which are key, are of
preventative nature and act by reinforcing the "immunity" of the agroecosystem. The
effects of many of these practices have been scientifically documented (Table II) and
tend to have wide geographic implications. Legume based crop rotations, one of the
simplest forms of biodiversification improve yields by the known action of interrupting
weed, disease and insect life cycles. However, they also can have subtle effects such as
enhancing the growth and activity of soil biology, including vesicular arbuscular
mycorrhizae (VAM), which allow crops to more efficiently use soil water and
nutrients.10 Agroecological technologies do not emphasize boosting yields under optimal
conditions as Green Revolution technologies do, but rather they assure constancy of
production under a wide range of soil and climatic conditions, and most especially under
marginal conditions which usually prevail in small farm agriculture (Figure 2). What is
important, however, is not to focus on particular technologies, but rather on an
assemblage of technologies that incorporate and emphasize crop diversity, use of
legumes in rotations, animal integration, recycling and use of biomass and residue
management.
The basic tenets of a sustainable agroecosystem are the conservation of renewable
resources, adaptation of the crop to the environment, and maintenance of a moderate but
sustainable level of productivity. The production system must: (1) reduce energy and
resource use, and regulate the overall energy input so that the output:input ratio is high
(2) reduce nutrient losses by effectively containing leaching,
runoff,
and erosion, and
improve nutrient recycling through the promotion of legumes, organic manure, compost,
and other effective recycling mechanisms (3) encourage local production of feed items
adapted to the natural and socioeconomic setting (4) sustain desired net output by
preserving the natural resources (by minimizing soil degradation) (5) reduce costs and
increase the efficiency and economic viability of small and medium-sized farms, thereby
promoting a diverse, potentially resilient agricultural system. Table III describes the
basic technical elements of the agroecological strategy.
From a management viewpoint, the basic components of sustainable agroecosystem
include: (1) vegetative cover as an effective soil-and water-conserving measure, met
through the use of no-till practices, mulch farming, and use of cover crops and other
appropriate methods (2) a regular supply of organic matter through the regular addition
of organic matter (manure, compost and promotion of soil biotic activity) (3) nutrient
recycling mechanisms through the use of crop rotations, crop/livestock systems based on
legumes, etc. (4) pest regulation assured through enhanced activity of biological control
agents, achieved by introducing and/or conserving natural enemies.
The ultimate goal of agroecological design is to integrate components so that overall
biological efficiency is improved, biodiversity is preserved, and the agroecosystem
SUSTAINABLE AGROECOLOGY171
TABLE I
A schematic outline of available alternative agriculture practices (modified after Coleman 1989).
r BIOLOGICAL
u
2
<
5
o
g
PEST
MANAGEMENT
(diseases,
insects
and
weeds)
PHYSICAL
L CHEMICAL
SOIL
FERTIITY
MANAGEMENT
CULTURAL
TECHNIQUES
L FERTILIZERS
Crop Rotation _
Soil Structure
Nature Controls
Cultivars
Soil Fertility
L Soil pH
Tillage
Cultivation
Thermal
Environment
Inert Dusts
Temporal
Barriers
Traps
- Manual Control
- Attractants
Botanicals
- Repellents
Crop Rotation
Drainage
Green Manures
Shallow Tillage
Deep Tillage
Crop Residues
Undersowing
- Primary Minerals -
Organic Wastes
Organic
Fertilizers
Commercial.
Products
r
[
allelopathy
crop residue management
agrophytocoenosis
[birds
insect and fungi
mammals
N-P-K
j trace elements
L organic matter
,-lime
L sulphur
[
implements
planting systems
transplanting
undersowing
[
grazing management
mowing
hedgerows
[
planting
harvest
cultural practices
light
adhesive
vacuum
crop
r rotenone
pyrethrum
ryania
sabadilla
quassia
nicotine
Bt
allelopathic herbicide
r- vegetables
-\ grains and livestock
L fruits
[
legumes
non-legumes
strip tillage
[
rotary tiller
chisel plow
subsoiler
vegetables
grains
fruits
- rock phosphate
basalt dust
granite dust
greensand
lime
L gypsum
r blood meal
bone meal
sea products
composted products
sul-po-mag
- Chilean nitrate
[
humates
soil conditioners
foliar sprays
soil testing services
SUSTAINABLE AGROECOLOGY173
U
a
o
E
a)
+->
to
>
M
o
o
a>
2
<
variable productivity
low adaptability
high productivity
high adaptability
B
marginalenvironmental gradientoptimal
FIGURE 2 Potential productivity and adaptability of agricultural technologies suited for a range of
environmental conditions (A: agroecological approach, B: Green Revolution approach).
productivity and its self-regulating capacity is maintained. The goal is to design an
agroecosystem that mimes the structure and function of local natural ecosystems; that is,
a system with high species diversity, biologically active and conserved soil which
promote recycling, and to prevent resource losses. Agroecologically designed systems
differ substantially from monoculture based conventional systems. Agroecological
systems are characterized by a solid foundation of biologically active soils which ensure
efficient nutrient recycling (vertical supports of barn). The rich biodiversity (roof)
provides stability and protection against environmental stress. Soil cover and animal or
tree integration (walls) minimize leakage from systems (Figure 3).
CONVERTING LARGE-SCALE CONVENTIONAL SYSTEMS TO
AGROECOLOGICAL MANAGEMENT
Modern conventional agroecosystems, which characterize much of the commercial
agricultural sector in industrialized and developing countries, are based on monoculture.
Due to this artificial structure, monocultures lack functional biodiversity and thus require
constant external inputs to perform. A major concern in sustainable agriculture is the
maintenance and/or enhancement of biodiversity and the role it can play in restoring the
ecological balance of agroecosystems so that stable production may be achieved.
Biodiversity performs a variety of renewal processes and ecological services in
agroecosystems (Figure 4). When they are lost, the costs can be significant.4
A major sustainable agriculture strategy is to restore agricultural diversity in time and
space through crop rotations, cover crops, intercropping, crop/livestock mixtures, and so
on, and to exhibit the following ecological features:
174 M. A. ALTIERI AND P. ROSSET
TABLE III
Basic technical elements of an agroecological strategy.
I. Conservation and Regeneration of Natural Resources
a. Soil (erosion, fertility and plant health)
b.
Water (harvesting, in-situ conservation, management, irrigation)
c. Germplasm (plant and animal native species, land races, adapted germplasm)
d. Beneficial fauna and flora (natural enemies, pollinators, multiple use vegetation)
II.
Management of Productive Resources
a. Diversification:
- temporal (i.e. rotations, sequences)
- spatial (polycultures, agroforestry, crop/livestock mixed systems)
- genetic (multilines)
- regional (i.e. zonification, watershed)
b.
Recycling of nutrients and organic matter:
- plant biomass (green manure, crop residues, N fixation)
- animal biomass (manure, urine, etc.)
- reutilization of nutrients and resources internal and external to the farm
c. Biotic regulation (crop protection and animal health):
- natural biological control (enhancement of natural control agents)
- artificial biological control (importation and augmentation of natural enemies, botanical
insecticides, alternative veterinary products, etc.)
III.
Implementation of Technical Elements
a. Definition of resource regeneration, conservation and management techniques tailored to local needs
and agroecological-socioeconomic circumstances.
b.
The level of implementation can be at the micro region, watershed, farm, and cropping system level.
c. The implementation is guided by a holistic (integrated) conception and therefore does not emphasize
isolated elements.
d. The strategy must be in agreement with the peasant rationale and must incorporate elements of
technical resource management.
a. Crop Rotations. Temporal diversity incorporated into cropping systems, providing
crop nutrients and breaking the life cycles of several insect pests, diseases, and weed life
cycles."
b.
Polycultures. Complex cropping systems in which two or more crop species are
planted within sufficient spatial proximity to result in competition or complementation,
thus enhancing yields.12'13
c. Agroforestry Systems. An agricultural system where trees are grown together with
annual crops and/or animals, resulting in enhanced complementary relations between
components increasing multiple use of the agroecosystem.1
d. Cover Crops. The use of pure or mixed stands of legumes or other annual plant
species under fruit trees for the purpose of improving soil fertility, enhancing biological
control of pests, and modifying the orchard microclimate.'5
e. Crop/Livestock Mixtures. Animal integration in agroecosystems aids in achieving
high biomass output and optimal recycling.16
The process of converting a conventional crop production system that relies heavily
on synthetic, petroleum-based inputs to a system with low-inputs is not merely a process
of withdrawing external inputs without compensatory replacement or alternative
management. Considerable ecological knowledge is required to direct the array of
natural flows necessary to sustain yields in a low-input system.
The process of conversion from a high-input conventional management to a low-
external input management is a transitional process with four marked phases (Figure 5).
SUSTAINABLE AGROECOLOGY175
HIGH INPUT/CONVENTIONAL AGROECOSYSTEM
I
SUSTAINABLE AGROECOSYSTEM
ECOSYSTEM
Biodiversity
Protection from leakiness
Nutrient supply
V7A
(inorganic
biological)
SoilFoundation
FIGURE 3 Comparison of agroecological features between a conventional and a sustainable agroecosystem
using the analog of a barn structure (modified after Edwards et al, 1993).
176M. A. ALTIERI AND P. ROSSET
COMPONENTSSoil
MesofaunaSoil
Microfauna
FUNCTIONS
Pollination
Genetic
introgression
Population
regulation
Biological
control
Biomass
consumption
Nutrient
cycling
Competition
Allelopathy
Sources of
natural enemies
Crop wild
relatives
t
Soil
structure
Nutrient
cycling
Decomposition
Predation
Nutrient
cycling
Nutrient
cycling
Disease
suppression
ENHANCEMENTIntercropping Agroforestry Rotations Cm" No-tillage Composting Gr8en.
Or°anio
Windbreaks
crops manuring matter
addition
FIGURE 4 Components and function of biodiversity in multiple use farming systems.
INCREASE IN BIODIVERSITY
3
Q
O
rr
a.
CONVENTIONAL
4-
ORGANIC
Progressive
elimination
of inputs
Efficient
use of
inputs
Input
substitutionSystem
redesign
TIME ^
FIGURE 5 Stages in the agroecological conversion of conventional agricultural systems.
(i) Progressive chemical withdrawal.
(ii) Rationalization and efficiency of agrochemical use through integrated pest
management (IPM) and integrated nutrient management
(iii) Input substitution, using alternative, low-energy input technologies
SUSTAINABLE AGROECOLOGY 177
(iv) Redesign of diversified farming systems with an optimal crop/animal integration
which encourages synergisms so that the system can sponsor its own soil fertility, natural
pest regulation, and crop productivity.
During the four phases, management is guided in order to ensure the following
processes:
(i) Increasing biodiversity both in the soil and above ground
(ii Increasing biomass production and soil organic matter content
(iii) Decreasing levels of pesticide residues and losses of nutrients and water
components.
(iv) Establishment of functional relationships between the various plant and animal
farm components.
(v) Optimal planning of crop sequences and combinations and efficient use of
locally available resources.
Most of existing IPM programs, which aim at maintaining mean levels of pest
abundance below the economic threshold, have concentrated on the scouting of crops to
determine pest densities in order to take action (usually an insecticide application) when
the economic threshold has been surpassed." Although IPM has failed to integrate the
original objectives and concerns of the original IPM definition (a combination of
methods to supplement the effects of natural control agents), it has contributed toward
the rationalization of pesticide use by emphasizing timely applications and use of
selective materials. This in itself has allowed for, in many cropping systems such as
cotton, alfalfa, corn, apple, soybean, and tomato, for example, recovery of beneficial
fauna to take place.
It is important to note that the conversion process can take anywhere from 1-5 years
depending on the level of artificialization and/or degradation of the original high-input
system. For example, if the system being converted was previously sprayed with a highly
persistent insecticide, (i.e. hydrochlorinated insecticides), the slow degradation process
of the pesticide and its metabolites may considerably delay the conversion. In addition,
not all input substitution approaches are ecologically sound. It is well established that
some practices widely encouraged by organic farming enthusiasts such as flame-weeding
and applications of broad spectrum botanical insecticides can have serious side effects
and environmental impacts. There is some concern about the impacts that certain
botanical preparations (i.e. ryannia, quassia, rotenone, pyrethrum, etc.) may have on
predators and parasitoids.
A key challenge in the transition process is to maintain an economic equilibrium in
order to assist farmers in absorbing the possible income loss due to slightly lower yields
in the initial conversion phase. Incentives and/or subsidies may be needed for some
farmers as they wait for their productive systems to generate the gains that the
conversion process assures (Figure 6).
TWO DIVERSIFICATION STRATEGIES FOR AGROECOLOGICAL CONVERSION
1.
Cover Cropping in Orchards and Vineyards
Cover cropping is the practice of growing pure or mixed strands of legumes, cereals, or
natural vegetation to protect the soil against erosion; ameliorate soil structure; enhance
soil fertility, and suppress pests, including weeds, insects, and pathogens. Cover crops
178M. A. ALTIERI AND P. ROSSET
ra
agroecological management
conventional management
Time
FIGURE 6 The hypothetical dynamics of farmers income during the conversion process from conventional to
agroecological management.
can improve soil structure and water penetration, prevent soil erosion, modify the
microclimate and reduce weed competition (Figure 7). Besides these effects, cover crops
can impact the dynamics of orchards and vineyards in two major ways.
(i) Enhanced Soil Biology and Fertility. The value of cover crops in maintaining soil
fertility in orchards depends partly on the production of reasonably heavy tonnage of
organic matter. Purple vetch can produce 20 tons of green manure per acre, whereas
other legumes produce from 12 to 13 tons per acre. Purple vetch and sweet clover can
produce net gains of nitrogen of up to 150 pounds/acre/year.
Experiments in vineyards of the Aconcagua Valley in Chile using Vicia atropurpurea
as a cover crop shows that the purple vetch serves as an abundant source of organic
matter, crucial to activate soil biology and nutrient mineralization. Soil organic matter
content increased from 2.4% in the conventional vineyard to 3.4% in the cover crop
treatment in just 6 months. A richer soil organic substrate stimulated populations of
mesofauna (Oribatei, Tarsonemini, Acaridae and Prostigmata) in vineyards with a
permanent cover. These positive effects on soil biology and fertility determined that
vineyards subjected to conversion with an undersown cover crop exhibited a 10-20%
yield increase during the first two years of conversion (Figure 8), and size and quality (%
sugar) of table grapes in the organic plots was of higher quality than in the conventional
plots.18
In California, almond orchards with a dense vetch cover or with lush resident
vegetation had abundant populations of earthworms (Aporrectoda turgida and
Microscolex dubius), whereas frequently disked conventional orchards had very few
earthworms. These differences in earthworm abundance affected orchard soil aeration
and recycling of organic materials.19
(ii) Enhanced Biological Control of Insect Populations. Entomological studies
conducted in orchards with ground cover vegetation indicate that these systems exhibit
SUSTAINABLE AGROECOLOGY179
t
Enhancement of
Soil Structure
o Improve aggregation
o Increase macropores
° Improve water
infiltration
o Reduce* soil crust
° Decrease runoff
° Reduce interrill and rill
erosion
Benefits of
Cover Croos
ii
Improvement in
Soil Fertility
*
Pest
Management
0 Provide crop residue mulch Preserve a favorable
to regulate temperaturebalance between pests
and conserve water and predators
o Increase nitrogen fixation 0 Enhance biological diversity
° Nutrient recycling
° Maintain soil organic matter
FIGURE7 Potential benefits of cover crop (Lai etal., 1991).
VINEYARD I
40000
35000-
30000-
25000-
f
20000-
15000-
10000-
5000-
0
1"3"94
SEASON
1994"95
1 Organic
Conventional
VINEYARD II
1"3"94 SEASON 1994"95
FIGURE 8 Production trends of two vineyards in central Chile during two seasons after conversion initiation.
180 M. A. ALTIERI AND P. ROSSET
lower incidence of insect pests than clean cultivated orchards. This is due to an
abundance and efficiency of predators and parasitoids enhanced by the rich floral
undergrowth, or in some cases because certain pests are discouraged when the orchard
floor is rendered with plants other than naturally occurring wild host plants. In
California's Central Valley vineyards, variegated leafhopper population differences
between cover and noncover plants were clearly different for all three leafhopper broods,
but the reasons behind these differences were not so clear. Anecdotal reports from
growers in the area suggest that weedy cover crops in early to mid-season may have
smaller populations of leafhoppers. An increase in the abundance of generalist predators,
especially spiders, may help reduce leafhopper populations in the weed-cover plots.20 In
the same area, leaving a managed ground cover of Johnson or Sudan grass, a minor
cultural practice modification in vineyards, resulted in a habitat modification which
greatly enhanced the activity of predators against phytophagous mites such as the
Willamette mite. When Johnson grass (Sorghun halepense) was allowed to grow in grape
vineyards, there was a buildup of alternate prey mites, which supported populations of
the predatory mite Metaseiulus occidentalis, which, in turn, restrained the Willamette
mite,
Eotetranychus Willamette, to noneconomic numbers.4
In California almond orchards, the percentage of fruit rejection due to navel
orangeworm (Ayeolis transitella) and peach twig borer (Anarsia lineatella) damage was
much lower in cover cropped orchards than in conventional clean cultivated ones.
Populations of spider mites and San Jose scale also remained low in the orchards with
cover crops due to the high diversity and abundance of generalist predators such as
ladybird beetles, lacewings, Geocoris spp, Stethorus picipes, Metaseiulus occidentalis,
and Scolothrips sexmaculatus.19 Studies in Chile's Aconcagua Valley showed that pests
such as the grape mealy bug (Pseudococcus maritimus) was controlled by natural
enemies harbored by the cover crops, but at times mass releases of Pseudaphycus
flavidulus parasitoids were needed to control foci in some sectors of the vineyard (Figure
9).
Botrytis, the main disease, is buffered with canopy management which permits
ventilation thus favorably modifying the microclimate and/or with applications of
compost-based preparations containing antagonists (Trichoderma, Pseudomonas, etc.)
However, after two years under cover crop management, input substitution is necessary
only in "spot trouble areas" of the vineyard.18 Eventually, the biological structuring of the
vineyard sponsors the performance of the agroecosystem.
Research suggests that cover crops transform vineyards into agroecosystems of
increasing ecological diversity and stability. In fact, cover crops function as a major
"ecological turn table" which activates and influences key processes and components of
the vineyard agroecosystem: provision of habitat for beneficial insects, activation of soil
biology, addition of organic matter, N fixation, soil protection, microclimate
modification etc. (Figure 10). Clearly then in vineyards and orchards, cover cropping is a
simple but key diversification practice that triggers profound positive ecological changes
in the agroecosystem.21
2.
Integrating Livestock and Crop Production
Farms specializing in monoculture and/or simple crop rotations seldom include livestock
as an integral part of the system. The exclusion of livestock as an essential part of the
enterprise deprives farmers from gaining the benefits of animal manure and better
utilization of forages produced. Pastures can be inextricably linked with crops and their
residues in many farming systems. Pastures may be intercropped or sown in pure stands
SUSTAINABLE AGROECOLOGY181
12 -i
10 -
8 -
6 -
4 -
0 -
conventional
clusters eggs nymphs females males
FIGURE 9 Abundance levels of various life stages of the mealybug in conventional and organic vineyards in
central Chile.
Green Cover Crop
Microclimate
Modification
Soil Structure
t
Erosion Protection
Beneficial
Insect
Complex
Soil Organisms
Earth Worms
Organic Matter
and
Nitrogen Cycle
FIGURE 10 The ecological turntable effects in a diversified vineyard triggered by a green cover crop.
182 M. A. ALTIERI AND P. ROSSET
in a cropping sequence for one or more years. When integrated into cropping systems
pastures have the potential to:
a. Replenish soil fertility, particularly with respect to nitrogen, from legume
dinitrogen fixation, and the more rapid cycling of nutrients via returns of dung and urine
of the grazing animal. Research in Mediterranean ecosystems shows conclusively that
various years of growth of legume based rotations in wheat-pastures systems increase
total soil nitrogen and legume pastures have the potential to contribute significantly to
subsequent grain yield of wheat.
b.
Improve soil structure and stability. This is demonstrated by an increase in the
percentage of water-stable soil aggregates during a pasture phase of varying years in
contrast to a decline in water-stable aggregates and thus in soil structure associated with
continuous cropping of wheat. In addition dead pasture mulch can alter the soil surface
radiation balance so as to retard rises in soil temperature and soil strength by slowing
drying. These changes enhance crop germination.
c. Break pest or disease cycles and provide better weed management for the current
or subsequent crop.
d. Supplement and upgrade the quality of crop residues or native grasslands. The
legume may be harvested during crop growth or after crop harvest to supplement crop
by-products or the lower quality crop residues. Legumes may also be oversown into
maturing crops to utilize residual soil moisture.
These benefits of pasture integration can be realized when livestock, crops, animals
and other farm resources are assembled in mixed and rotational designs to optimize
production efficiency, nutrient cycling and crop protection. In Chile, the Centro de
Education y Tecnologia (CET) on NGO involved in rural development has been training
farmers to diversity their farms with animals, crops and trees, and to optimize
bioresource flows, interactions and complementarities among farm components. By
helping farmers to design and adopt a crop-pasture rotation, which is the key to breaking
pest life cycles and enhancing soil fertility, the pasture "charges" the system with organic
matter and nutrients (Figure 11). Crops constitute the "extractive" phase although they
bring the benefits of crop and residue production, soil cover, trap cropping, etc. Animal
integration is crucial, although cattle races are carefully selected for size and nutritional
needs in order not to place too high a demand on the pasture resources. Rotation grazing
proves an effective way to constantly avail cattle with food, to allow rapid pasture
regrowth and to evenly distribute manure in the field.
This design has proven effective in Chiloe Island, south Chile, where phosphorous
levels and crop production increase dramatically after a six year crop-pasture rotation in
phosphorous deficient marginal lands (Figure 12). After the sixth year, potato yields
increase double fold and only half of the chemical fertilizer and cow manure are needed
to sustain such yields (Table IV). After a third complete rotation cycle, it is expected that
no external inputs will be needed to maintain acceptable production levels. Biological
structuring will sponsor the system's performance.
CONCLUSIONS
An agroecological strategy to achieve sustained agricultural productivity combines
elements of both traditional and modern technologies. Realistically, however, a
successful strategy requires more than simply modifying or adapting existing
technologies. Novel agroecological approaches aim at breaking the monoculture
SUSTAINABLE AGROECOLOGY
Fruit and Forest Trees, Berries, Vines, etc.
183
in
i
FIGURE 11 Basic design of an integrated farm with spatial and temporal designs of crops, pasture, animals
and trees. The pasture constitutes the "charging phase" of the rotation while the crops constitute the "extractive
phase". Animals are managed with rotational grazing.
17 -
B
m
O
5 -
3 -
After 6th year
Initial 6 years
SIX-YEAR CROP ROTATION ON ONE FIELD
Summerpotatowheatforage oats
Winter Crops
or FallowLI
permanent native pasture
I I
Years
FIGURE 12 The dynamics of phosphorus (the limiting nutrient factor) in a small farm rotational sequence of
crops and pasture during and after a sixth year rotational phase in Chiloe Island, Chile.
184 M. A. ALTIERI AND P. ROSSET
TABLE IV
Crop productivity and fertilizer inputs in a rotational design during the
first six year phase and after the sixth year in Chiloe Island, Chile.
Yields kg/ha3 Initial six years After sixth year
Potatoes
Wheat2
Forage oats
Native pasture
20,000
1,500
7,000
3,000
40,000
2,400
10,000
12,000
' Fertilizer input: 450 kg/ha P2O5, 120 kg/ha N, 20 t/ha manure,
fertilizer input: 250 kg/ha P2O5, 70 kg/ha N, 12 t/ha manure.
3 Dry matter
structure by designing integrated farming systems such as those described herein,
otherwise, the role of alternative agricultural practices will be limited only to input-
substitution. Input-substitution does not take advantage of the effects of the integration of
plant and animal biodiversity which enhances complex interactions and synergisms and
optimizes ecosystem functions and processes, such as biotic regulation of harmful
organisms, nutrient recycling, and biomass production and accumulation, thus allowing
agroecosystems to sponsor their own functioning. The end result of agroecological
design is an improved economic and ecological sustainability of the agroecosystem, with
proposed management systems specifically in tune with the local resource base and
operational framework of existing environmental and socioeconomic conditions.
Management components must be organized into an agroecological strategy that
highlights the conservation and enhancement of local agricultural resources (germplasm,
soil, beneficial fauna, plant biodiversity, etc.) emphasizing a development methodology
that encourages participation, use of traditional knowledge, and adaptation of farm
enterprises that fit local needs and conditions.
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... Within the European Union (EU), both the Farm-to-Fork strategy (EC, 2020a) and the Biodiversity Strategy (EC, 2020b) highlight the importance of agroecological approaches. Agroecological farming practices include crop-livestock integration, low-input management, reliance on local resources and diversification (Altieri and Rosset, 1996). Despite recent attempts to define and describe it more closely (FAO, 2018b;Wezel et al., 2020), agroecology comes in many forms and context-specific implementations (Bezner Kerr et al., 2021;Lampkin et al., 2020;Gallardo-López et al., 2018). ...
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Agroecology has been proposed as a strategy to improve food system sustainability, but has also been criticised for using land inefficiently. We compared five explorative storylines, developed in a stakeholder process, for future food systems in the EU to 2050. We modelled a range of biophysical (e.g., land use and food production), environmental (e.g., greenhouse gas emissions) and social indicators, and potential for regional food self-sufficiency, and investigated the economic policy needed to reach these futures by 2050. Two contrasting storylines for upscaling agroecological practices emerged. In one, agroecology was implemented to produce high-value products serving high-income consumers through trade but, despite 40 % of agricultural area being under organic management, only two out of eight EU environmental policy targets were met. As diets followed current trends in this storyline, there were few improvements in environmental indicators compared with the current situation, despite large-scale implementation of agroecological farming practices. This suggests that large-scale implementation of agroecological practices without concurrent changes on the demand side could aggravate existing environmental pressures. However, our second agroecological storyline showed that if large-scale diffusion of agroecological farming practices were implemented alongside drastic dietary change and waste reductions, major improvements on environmental indicators could be achieved and all relevant EU policy targets met. An alternative storyline comprising sustainable intensification in combination with dietary change and waste reductions was efficient in meeting targets related to climate, biodiversity, ammonia emissions, and use of antibiotics, but did not meet targets for reductions in pesticide and fertiliser use. These results confirm the importance of dietary change for food system climate mitigation. Economic modelling showed a need for drastic changes in consumer preferences towards more plant-based, agroecological and local foods, and for improvements in technology, for these storylines to be realised, as very high taxes and tariffs would otherwise be needed.
... (Altieri and Rosset 1996;Gliessman 1998;Lancon et al. 2007) . ...
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In the present study, natural active enemies of pests in sugar beet fields in some regions of Iran including Gonbad, Ramian, Agha Qala (Golestan province), Nahavand (Hamadan province), Fereydoun-Shahr, Borkhar, Golpayegan (Isfahan province), Shahrekord (Chaharmahal & Bakhtiari province), Naghadeh, Miandoab (West Azarbaijan province) were studied. A total of 45 species of natural enemies including 10 parasitoids and 35 predators of the order, Hymenoptera (Braconidae: seven species in six genera; Ichneumonidae: single species), Diptera (Tachinidae: two species in two genera; Asilidae: four species in four genera; Syrphidae: three species in three genera), Coleoptera (Carabidae: seven species in six genera; Coccinellidae: five species in four genera), Hemiptera (Anthocoridae: six species in two genera; Miridae: five species in three genera; Nabidae: two species in two genera; Reduviidae: two species in two genera), and Neuroptera (single species from the family Chrysopidae) were collected and identified in different parts of the country. Due to high diversity of natural enemies in sugar beet fields, the support of these beneficial insects is necessary in order to reduce the consumption of chemical pesticides, and the success of natural enemies effectiveness.
... A guiding principle must be to work with people in transitions and with democratic openness towards other ways of thinking. In very concrete ways transitions from extractivism and mastery have to be meaningful to people in their lives -citizens, practitioners, policy makersfor concrete, political and societal change to happen (Altieri & Rosset, 1996;Toffolini et al., 2017). In this context, a return to the meaning in, of, and attentiveness to the living soil, can serve as guide facilitating transition to new ways of organizing human practice. ...
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The hegemony of the agribusiness model in Latin America has consolidated the implementation of the Green Revolution technological package in which pesticides play a fundamental role. Yet in the face of its negative social, economic, and environmental effects, many medium-capitalized producers, petty commodity producers, and peasants have developed various food production strategies beyond extensive pesticide use. Drawing from the convergence between rural sociology and agroecology, we address the narratives and practices of farming families that are constructing alternatives to pesticides. Our analysis focuses not only on the productive dimension but also on the political and cultural aspects of the strategies that the subjects deploy when distancing themselves from the hegemonic practices of agribusiness. To approach this objective, we combine an analysis of in-depth interviews and ethnographic notes carried out in the municipality of Putaendo (Valparaiso, Chile) and the Antinaco-Los Colorados valley (La Rioja, Argentina). The article contributes to previous theoretical work on alternative agriculture by analyzing practices and narratives as seen from four different levels: microeconomics, macroeconomics, politics, and family labor. Drawing from a combination of these perspectives, the agrarian producers in our study explain and exemplify the growth, deployment, threats and staying power of practices distinct to or in opposition to agribusiness. Additionally, the research confirms that the analysis of alternatives for changing agriculture should consider the interaction between technical components, such as the reduction or elimination of chemical pesticides, economic balance, such as providing an “adequate” level of income, and cultural elements, such as the co-existence of economic systems.
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Yields in modern agricultural systems are sustained by investing costly external resources of uncertain future availability and with technologies that have prompted ecosystemic degradation. The ecological and socioeconomic aspects of developing alternative, self-sustained, energy efficient, less resource-intensive agroecosystems are analyzed.
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The practice of growing two or more crops together is widespread throughout the tropics and is becoming increasingly practised in temperate agriculture. The benefits of nutrient exchange, reduced weed competition and pathogen control can generate substantial improvements in growth and yield. In this book John Vandermeer, a leading worker on the subject, shows how classical ecological principles, especially those relating to competition and population ecology, can be applied to intercropping. Despite the large amount of research activity directed towards the subject over the last 20 years, the practice of intercropping has, until now, received very little serious academic attention. The Ecology of Intercropping is unique in approaching the question of intercropping from a theoretical point of view. In addition the details of the approach will take as their starting point well-accepted ecological theory. Using this basis the author shows how the approach can be used to design and evaluate intercropping systems to improve agricultural yields.
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'The Green Revolution' of the 60's and 70's produced immense gains in food cereal production in the Third World. But there are huge problems in the 'post-revolutionary' era: farmers with small or marginal holdings have benefited less than wealthier farmers; intensive mono-cropping has made production more susceptible to environmental stresses and shocks. Now there is evidence of diminishing returns from intensive and intensively chemical agricultural production. What is needed is a new approach, equally revolutionary, but different in its ideas and style. The authors set out what they mean by 'sustainable' agriculture in the new era and look at the effects of international economic restraints and of national policies on the kind of development they see as necessary. They chart a path for sustainable livelihoods for Third World farmers enmeshed by forces outside their control. They describe methods of evaluating and resolving the tough trade-offs all levels of intervention, from international trade down to the individual farm. This book cannot provide all the answers, but it does indicate what international conditions we need to be aware of, what national policies we need to advocate and what approaches at the local level we need to adopt to ensure the goal of agricultural sustainability. Originally published in 1990. © 1990 by Gordon R. Conway and Edward B. Barbier. All rights reserved.
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California almond growers commonly use organophosphate pesticides, which can be disruptive to biological control. Sprays during the spring and summer kill beneficial arthropods, including parasitic and predatory insects and spiders. In addition, pesticides have been detected by Cal EPA in winter fog and in runoff water flowing into the rivers of the San Joaquin Valley, which may lead to further restrictions in pesticide use. However, some almond growers are able to grow nuts with low insect damage without using toxic insecticide sprays. This article reports the results of a 6-year study, begun in 1988, of three almond orchards in Merced County to identify grower practices that permit reduced pesticide use.