Agroforestry note elie.pptx

AGROFORESTRY LEVEL: II
COMPONENT: INTRODUCTION TO
AGROFORESTRY
name: NIYIBIZI Elie
email: mniyibizieli@gmail.com
tel:0733393513
0790010303

CONTENT
CHAPTER 1 : INTRODUCTION
CHAPTER 2: CLASSIFICATION OF AGROFORESTRY SYSTEMS
2. 1. STRUCTURE
2. 2. FUNCTION
2. 3. ECOLOGICAL SPREAD
2. 4. SOCIO ECONOMIC NATURE
CHAPTER 3: TREE-CROP INTERACTION
CHAPTER 4: NUTRIENT CYCLING IN TROPICAL
AGROFORESTRY SYSTEMS
CHAPTER 4 : BENEFITS AND CHALLENGES OF

...WELCOME TO SEASION OF AGROFORESTRY...
CHAPTER 1: INTRODUCTION
Definition of Agroforestry
Agroforestry:
the word coined in early seventies, has made its place in all the developed and the developing
countries of the world. A few definitions of agroforestry are as under:
l A sustainable management system for land that increases overall production, combines
agricultural crops, tree crops and forest plants and/or animals simultaneously/or sequentially and
applies management practices that are compatible with cultural patterns of local population".
l Agroforestry is a collective name for land-use systems and technologies in which woody
perennials including trees, shrubs, bamboos etc. are deliberately combined on the same land-
management unit with herbaceous crops or animals either in some form of spatial arrangement or
temporal sequence."

• Agroforestry is a land-use that involves deliberate retention, introduction, or mixture of trees
or other woody perennials in crop/animal production field to benefit from the resultant
ecological and economical interactions".
• Agroforestry is a dynamic, ecologically based, natural resource management practice that,
through the integration of trees on farms and in the agricultural landscape, diversifies and
sustains production for increased social, economic and environmental benefits".
• In agroforestry systems there are both ecological and socio-economic interactions
between different components. This implies that
• Agroforestry normally involves two or more species of plants (or plants and animals), at
least one of which is a woody perennial;
• An agroforestry system always has two or more outputs:
 The cycle of an agroforestry system is always more than one year
 And
 even the simplest agroforestry system is structurally, functionally, and socio
economically more complex than a mono-cropping system.

 Agroforestry is a form of multiple cropping which satisfies three basic conditions:
 (i) there exists at least two plant species that interact biologically
 (ii) at least one of the plant species is a woody perennial
 (iii) at least one of the plant species is managed for forage, annual or perennial crop
production.
 Agroforestry is a collective name for land-use systems in which woody perennials (trees,
shrubs, etc.) are grown in association with herbaceous plants (crops, pastures) and/or livestock
in a spatial arrangement, a rotation or both, and in which there are both ecological and
economic interactions between the tree and non-tree components of the system.
 Agroforestry referes to collection name for land-use systems of mixture of tree,crop and even
liverstock farming in the same space for economic purpase.
 It shows that agroforestry is a new name for a set of old practices. In simple terms
Agroforestry is "an efficient land-use system where trees or shrubs are grown with arable
crops, seeking positive interactions in enhancing productivity on the sustainable basis.
Agroforestry combines agriculture and forestry technologies to create
more integrated, diverse, productive, profitable, healthy and sustainable
land-use systems.

The objective is to create sustainable land management strategies which increase the overall yields
of the land and which are also compatible with the environment and local cultural practices.
Properly applied, it is a system that is both productive and environmentally sound and has the
potential not only to increase food, fuel and income for farmers or herders on marginal lands but
also to help stop the destruction of the world’s forest lands.
Agroforestry practices are intentional systematic combinations of trees with crops and/or livestock
that involve intensive management of the interactions between the components as an integrated
agro ecosystem. These key features are the essence of agroforestry and are what distinguish it
from other farming or forestry practices.
To be called agroforestry, a land-use practice must satisfy following criteria:

Combinations of trees, crops and/or animals are intentionally designed and
managed as a whole unit, rather than as individual elements that may occur in close proximity
but are controlled separately.
Agroforestry practices are intensively managed to maintain their productive and
protective functions; these practices often involve annual operations such as cultivation and
fertilization.
Agroforestry management seeks to actively manipulate the biological and
physical interactions between the tree, crop and animal components. The goal is to enhance
the production of more than one harvestable component at a time, while also providing
conservation benefits such as non-point source water pollution control or wildlife habitat.
The tree, crop and/or animal components are structurally and functionally
combined into a single, integrated management unit. Integration may be horizontal or vertical,
and above or below ground. Such integration utilizes more of the productive capacity of the
land and helps balance economic production with resource conservation.

Land
Agroforestry is not a system of pots on a balcony or in a greenhouse. It is a system by which land
is managed for the benefit of the landowner, environment and long-term welfare of society.
Agroforestry can make better use of under-utilized land, especially by improving productivity on
land considered marginal for agricultural production. While appropriate for all landholdings, this
is especially important in the case of hillside farming where agriculture may lead to rapid loss of
soil. If the farmer owns the land, she/he has a vested interest in thinking conservatively, how the
land can be maintained over long periods of time. Unfortunately, farmers who rent land may have
less interest in the long-term benefits of agroforestry and may even fear that making
improvements will raise the rent or result in the lease being terminated.
Trees
In agroforestry, particular attention is placed on multiple purpose trees or perennial shrubs. The
most important of these Trees are the legumes because of their ability to fix nitrogen
and thus make it available to other plants.

The roles of trees on the small farm may include the following:
l Sources of fruits, nuts, edible leaves, and other food.
l Sources of construction material, posts, lumber, and thatching.
l Sources of non-edible materials including sap, resins, tannins, insecticides, and medicinal
compounds.
l Sources of fuel.
l Beautification.
l Shade.
l Soil conservation, especially on hillsides.
l Improvement of soil fertility.
In order to plan for the use of trees in agroforestry systems, considerable knowledge of their
properties is necessary. Desirable information for each species includes its benefits, adaptability to
local conditions (climate, soil, and stresses), the size and form of the canopy and root system, and
suitability for various agroforestry practices.

Some of the most common uses of trees in agroforestry systems are:
l Individual trees in home gardens, around houses, paths, and public places.
l Dispersed trees in cropland and pastures.
l Rows of trees with crops between (alley cropping).
l Living fences and borderlines, boundaries.
l Windbreaks.
l Improved fallows.
l Terraces on hills.
l Erosion control on hillsides, gullies, channels.
l Woodlots for the production of fuel and timber.

Non-trees
Any crop plant can be used in agroforestry systems. The choice of crop plants in designing such
systems should be based on those crops already produced in a particular region either for
marketing, feeding animals, or for home consumption, or that have great promise for production
in the region. In keeping with the philosophy of agroforestry, however, other values to be
considered in crop selection include proper nutrition, self-sufficiency and soil protection. Thus,
selection of crops requires a judgment based on knowledge of the crops,
adaptations, production uses, as well as family needs, opportunities for barter,
and markets.
Any farm animal can be used in agroforestry systems. The choice of animal will be based
on the value the farmer places on animal-derived benefits including income, food,
labor, non-food products, use of crop residues, and manure.
Agroforestry attributes

There are three attributes which, theorically, all agroforestry systems possess.These are:
u Productivity:
Most of all agroforestry systems aim to maintain or increase production (of preferred
commodities) as well as productivity (of land). These include: increased output of tree products,
improved yields of associated crops, reduction of cropping system inputs, and increased labor
efficiency.
u Sustainability:
By conserving the production potential of the resource base, mainly through the beneficial effects
of woody perennials on soils, agroforestry can achieve and indefinitely maintain conservation and
fertility goals.
u Adoptability:
The word “adopt” here means “accept” and it may be distinguished from another commonly used
word adapt, which implies “modify” or “change”. The fact that agroforestry is a relatively a new
word for an old set of practices means that, in some cases, agroforestry has already been accepted
by the farming community. However, the implication is that improved or new agroforestry
technologies that are introduced into new areas should also conform to local practices.
These attributes are so characteristics of all agroforestry systems that they form the basis for

CHAPTER 2: CLASSIFICATION OF AGROFORESTRY SYSTEMS
Several criteria can be used to classify and group agroforestry systems and practices. The most
commonly used ones are:
1. Structure
Structure- this refers to the composition of the components, including spatial arrangement of the
woody component, vertical stratification and temporal arrangement of the different components.
2. Function
Function- refers to the major function or role of the system, mainly of the woody components
(which can be productive, e.g. production of food, fodder, fuelwood, and so on; or protective, e.g.
windbreak, shelterbelt, soil conservation hedges, etc.).
3. Ecological spread
Socioeconomic nature – refers to the level of inputs of management (low-input, high-input) or
intensity on scale of management and commercial goals (subsistence, Commercial, intermediate).
4. Socio economic nature.
Ecological spread – this refers to the environmental conditions and ecological suitability of the
systems on the assumption that certain types of systems can be more appropriate for certain
ecological conditions (e.g. asset of agroforestry systems for arid and semi-arid lands, tropical
highlands, lowland humid tropics, and so on.

These broad bases on classification of Agroforestry
systems are by no means independent. It is obvious that
they have to be interrelated because the structural and
functional bases relate to the woody components in the
system whereas the socio economic and ecological
stratification refer to the organization of the systems
according to the socioe conomic and ecological
conditions.

2. 1. Classification of Agroforestry System on Structural Basis:
The structural of a system can be defined in terms of its components and the expected role or
function of each. In this system the type of component and their arrangement are important.
Hence, on the basis of structure, AF systems can be grouped into two categories:
A. Nature of components
And
B. Arrangement of components
A. Nature of the components: based on the nature of components, AF systems can be classified
into the following categories;
1.1 Agrisilvicultural systems
1.2. Silvopastoral systems and
1.3. Agrosilvopastoral systems
1.4. Other systems.

1.1 Agrisilvicultural system (crops and trees including shrubs/vines and trees) .
This system involves the conscious and deliberate use of land for the concurrent production of
agricultural crops including tree crops and forest crops.
(i) Shifting cultivation (slash and burn system):It refers to farming system in high rainfall areas
in which land under natural vegetation (usually forests) is cleared by slash and burn method
cropped with common arable crops for a few years and then left unattended when natural
vegetation regenerates. Due to the increasing trends of population pressure, the fallow period is
drastically reduced and system has degenerated causing serious soil erosion depleting soil
fertility resulting to low productivity.
(i) Improved fallow: Fallows are crop land left without crops for periods ranging from one
season to several years. The objective of improved fallow species in shifting cultivation is to
recover depleted soil nutrients. Once the soil has recovered, crops are reintroduced for one or
more seasons. The fallow periods vary from region to region but are presently becoming shorter
due to an increasingly acute land shortage. The best species for the fallow system should induce
good nitrogen fixation in the soil.

Species: while the main function of the fallow is to maintain or restore soil fertility and reduce
erosion, some plants can be introduced primarily for their economic value. Species choice should
not be exclusively confirmed to ‘soil improvers’; plants with marketable products should be
compatible with future crops, free of any negative physical or chemical effects on the soil and not
in competition with the crop to be planted later on the same site.
(i) Taungya: This is a modified form of shifting cultivation in which the labour is permitted to
raise crops in an area but only side by side with the forest species planted by it. This labour is
responsible for the upkeep of a plantation. The practice consists of land preparation, tree planting,
growing agricultural crops for 1-3 years, until shade becomes too dense, and then moving on to
repeat the cycle in a different area. In some cases crops may be grown one year before the trees
are planted.
(ii) Multipurpose tree species garden: In this system of agroforestry, various kinds of tree
species are grown mixed. The major function of this system is production of food, fodder and
wood products for home consumption and sale for cash.

(i) Alley Cropping (Hedgerow Intercropping): Alley cropping is an agroforestry technology in
which food crops are grown in alleys formed by hedgerows of trees and shrubs, preferably
nitrogen-fixing species. The hedgerows are cut back at planting and periodically pruned during
cropping to reduce shading and competition with crops for light, nutrients and moisture. The
hedgerows are allowed to grow freely to cover the land when there are no crops. Alley cropping
practices appear to be a rational alternative land use for improving agricultural sustainability while
at the same time being economically viable. Nevertheless, there are abundant tree-crop
combinations that have not been examined yet as well as a substantial amount of research needed
to fully assess their agro-ecological sustainability, economic potentials, and adoption by farmers
and landowners.
(ii) Multi-purpose Trees and Shrubs on Farmlands: In this system various multipurpose tree
species are scattered haphazardly or according to some systematic patterns on bunds, terraces or
plot/field boundaries. The major components of this system are multipurpose trees and other fruit
trees and common agricultural crops. The primary role of this system is production of various tree
products and the protective function is fencing, social values and plot demarcation. Examples of
multipurpose trees employed in agroforestry are: Leucaena leucocephala, Acacia albida, Cassia
siamea, Casuarina equisetifolia, Azadirachta indica, Acacia senegal, Cocos nucifera etc.

(i) Crop Combinations with Plantation Crops: Perennial trees and shrub crops, such as coffee,
tea, coconut and cocoa, are combined into intercropping systems in numerous ways.
Example in India: The coffee-based system is cash crop oriented, initially developed with Coffea
arabica, which notably requires shade, low variation of temperature and good soil fertility, all
requirements the forest can meet. Through a selective clearing of the forest, an appropriate
number of trees is kept and managed to control shade, with additional plantations of trees, if
necessary. In this system, tree and coffee canopies appear as an efficient cover to control soil
erosion, which naturally develops on steep slopes, and of weed development. Trees provide a
quite important amount of organic matter to the benefit of the coffee, as well as wood, fodder,
fruits and other by-products to the farmers who are, for the most part smallholders (having less
than 2 ha).
(ii) Wind-break: Windbreaks have been a traditional agroforestry practice for over 100 years.
Windbreaks or shelterbelts are characterized as linear plantings of trees and/or shrubs established
primarily for environmental purposes such as reducing wind speed, retaining soil moisture and
buffering extreme temperatures. Integrated as part of crop or livestock production systems, the
effects of windbreaks serve to enhance crop and animal production by protecting livestock and
crops from harsh environmental conditions in addition to reducing soil erosion from agricultural
fields. The important reasons for which wind-breaks are planted include:

 to protect livestock from cold winds,
 to protect crops and pastures from hot, drying winds,
 to reduce/prevent soil erosion,
 to provide habitat for wildlife,
 to reduce evaporation from farmlands,
 to improve the microclimate for growing crops and to shelter people and livestock, to retard
grass fires,
 for fencing and boundary demarcation.
(x)Soil Conservation Hedges: trees can be planted on physical soil conservation works (grass
strips, bunds. risers and terraces), wherein they play two roles: to stabilize the structure and to
make productive use of the land they occupy. Stabilization is through the root system. In some of
steeply sloping landscapes of the country, the risers or terraces are densely planted with trees, with
multiple use being made of them for fruit, fodder and fuelwood.

1.1 Silvopastoral System (trees + pasture and/or animals)

Silvopastoral systems are definitely the most prominent agroforestry practice. Silvopastoral
systems are characterized by integrating trees with forage and livestock production. Traditionally,
silvopastoral systems involved grazing livestock in wooded rangeland and incorporating trees in
pastures for shade and timber.
The production of woody plants-combined with pasture is referred to as a silvopastoral system.
The trees and shrubs may be used primarily to produce fodder for livestock or they may be grown
for timber, fuelwood, and fruit or to improve the soil. A silvopastoral system is needed in dry
areas, in particular to help meet wood and fodder demands throughout the year.
This system is again classified into three categories:
(i) Protein bank
(ii) Living fence of fodder trees and hedges
(iii)Trees and shrubs on pasture.

(i) Protein Bank: In this silvopastoral system of agroforestry, various multipurpose trees (protein-
rich trees) are planted on or around farmlands and rangelands for cut-and-carry fodder production
to meet the feed requirements of livestock during the fodder-deficit period.
(ii) Living Fence of Fodder Trees and Hedges: In this system various fodder trees and hedges
are planted as live fences to protect the property from stray animals or other biotic influences.
(iii) Trees and Shrubs on Pastures: In this system various tree and shrub species are scattered
irregularly or arranged according to some systematic pattern, especially to supplement forage
production.
1.1 Agrosilvopastoral System, (trees + crops + pasture/animals)
This system has been grouped into two subgroups:
(i) Home Gardens: This is one of the oldest agroforestry practices, found extensively in high
rainfall areas in tropical south and south-east Asia.

Many species of trees, bushes, vegetables and other herbaceous plants are grown in dense and
apparently random arrangements, although some rational control over choice plants and their
spatial and temporal arrangement may be exercised. Most home gardens also support a variety of
animals (cow, goat, sheep) and birds (chicken, duck). In some places pigs are also raised. Fodder
and legumes are widely grown to meet the daily fodder requirements of cattle. The waste
materials from crops and homes are used as fodder/feed for animals/birds and wastes are used as
manure for crops. Hence one may conclude from the foregoing that 'home gardens represent land-
use systems Involving deliberate management of multipurpose trees and shrubs in integrate
association with annual and perennial agricultural crops and, Invariably, livestock, within the
compounds of individual houses, the whole crop tree-animal unit being intensively managed by
family labour'.
(ii) Woody hedgerows: In this system various woody hedges especially fast-growing and
coppicing fodder shrubs and trees, are planted for the purpose of browse, mulch, green manure,
soil conservation etc. The main aim of this system is production of food/fodder/fuelwood and soil
conservation.

1.4 Other Systems
(i)Apiculture with Trees: in this system various honey (nectar) producing tree species frequently
visited by honeybees are planted on the boundary, mixed with an agricultural crop. The main
purpose of this system is the production of honey.
(ii) Aquaforestry: In this system various trees and shrubs preferred by fish are planted on the
boundary and around fish-ponds. Tree leaves are used as forage for fish. The main or primary role
of this system is fish production and bund stabilization around fish-ponds.
(iii) Multipurpose Wood Lots: In this system special location-specific MPTS are grown mixed
or separately planted for various purposes such as wood, fodder, soil protection, soil reclamation
etc.
B. Arrangement of Components:
The arrangement of components gives first priority to the plants even in AF systems involving
animals.
(i) Spatial Arrangement

Spatial practices are those in which it is primarily a combination in space. Spatial systems are
divided into mixed and zoned. In mixed spatial practices, the trees and herbaceous plants are
grown in intimate mixtures, with the trees distributed over more or less the whole of the land area.
In zoned spatial practices, the trees are either planted in some systematic arrangement, such as
rows, or are grown on some element in the farm, such as boundaries or soil conservation
structures.
(ii)Temporal Arrangement
Temporal arrangements of plants in AF may also take various forms. An extreme example is the
conventional shifting cultivation cycles involving 2-4 years of cropping and more than 15 years of
fallow cycle, when a selected woody species or mixtures of species may be planted. Similarly,
some silvopastoral systems may involve grass leys in rotation with some species of grass
remaining on the land for several years. These temporal arrangements of components in AF are
termed coincident, concomitant, overlapping (relay cropping), separate and interpolated.

۩ Coincident: it occur when different crops occupy the land together, e.g tea/coffee under tree,
pasture and tree or plantation crop combinations.
۩ Concomitant: when different components stay together for certain period, e.g taungya system
۩ Intermittent: when annual crops are grown with perennial ones , seasonal grazing of cattle in
pastures under trees.
۩ Interpolated: when different components occupy the space during different times, e.g
homogarden
۩ Separate: when components occupy space at different times, e.g improved fallow.
۩
۩
۩ II. Functional Classification of Agroforestry Systems: Two fundamental attributes
of all AF systems are productivity and sustainability. This clearly indicates that AF systems
have two functions.
۩ (a) Productive functions (producing one or more products): The various productive functions
of Af systems are: Food, Fodder, Fuelwoods, other woods, and other products.

(b) Protective functions (protecting and maintaining production systems): The protective
functions of AF systems are: Wind-break, Soil conservation, moisture conservation, Soil
improvement, Shade (for crop, animal and man).
III. Socioeconomic Classification of Agroforestry Systems: Based on such
socioeconomic criteria as scale of production and level of technology input and management,
agroforestry systems have been grouped into three categories:
(a) Commercial: The production is at large scale and for sale purpose
(b) Intermediate : it is an intermediate between commercial and subsistence systems. The
systems aim at the production of items, which are not only enough to meet the needs of the family,
but to earn money.
c) Subsistence. It aims at meeting the basic needs of small family having less holding and very
little capacity for investment.

IV. Ecological Grouping of Agroforestry Systems: Based on the major agroecological
zones, Agroforestry stems are grouped into the following categories:
(i)Humid/sub-humid lowlands: This region is characterized by hot humid climate for all or most
of the year and evergreen or semi-evergreen vegetation. The lowland humid and subhumid
tropics (commonly referred to as the humid tropics) are by far the most important ecological
region in terms of the total human population. It supports extent of area and diversity of
agroforestry and other land-use systems. Because of climatic conditions that favour rapid growth
of a large number of plant species, various types of agroforestry plant associations can be found in
areas with a high human population, e.g., various forms of home gardens, Plantation of crops with
combinations and multilayer tree gardens, in areas of low population density, trees on rangelands
and pastures.
(ii) Semi-arid/arid lands: This region is characterized by rainfalls confined to 9-21 days in July -
September, 2-4 wet months, vapour pressure deficit ranging from 9 mb in January to 30 mb in
April -May, solar radiation incidence (400-500 cal/cm2/day), high wind velocity (20 km/hour),
high potential evapotranspiration (6 mm/day) and high mean aridity Index (70-74.8%).
(iii).Highlands: Variable rainfall, degraded and shallow lands at high altitude to deep rich soils in
valleys and great climatic variations are the features of highlands. This area is a storehouse of
great biological diversity.

The areas in these high land tropics with significant AF potential are humid or subhumid; those
with dry climates have very low potential. land-use problems in the highlands are similar to those
in humid or dry lowlands, depending on climate, with the addition that sloping lands and steep
terrain make soil erosion a major concern.
AGROFORESTRY SYSTEMS AND PRACTICES
The words “systems” and “practices” are often used synonymously in agroforestry literature.
However, some distinction can be made between them:
1. An agroforestry practice is a distinctive arrangement of components in space and time.
2. An agroforestry system is a specific local example of a practice, characterized by
environment, plant species and arrangement, management, and social and economic functioning.
There are hundreds, possibly thousands, of agroforestry systems but only some 20 distinct
practices.
It should be noted that the distinction between systems and practices are vague, and even not very
critical for understanding and improving them. Therefore, the words, systems and practices are
used synonymously in Agroforestry.
3. Agroforestry technology- This refers to an innovation or improvement, usually through
scientific intervention, to either modify an existing system or practice, or develop a new one.

CHAPTER III: TREE – CROP INTERACTIONS IN AGROFORESTRY
When trees and crops are grown together on the same piece of land there will be interactions
between the two components, which may have positive or negative results. Interaction is defined
as the effect of one component of a system on the performance of another component and/or the
overall system.
Different types of interactions have been recognized between trees and crops in agroforestry
systems; namely:
this is positive effec
this is positive effec
1. Complementary
2. Supplementary
3. Competitive
4. Allelopathic this is negative effect

Two types of interactions between trees and crops in agroforestry systems are
positive in nature; namely:
1. COMPLEMENTARY INTERACTION
It exists if the presence of one crop increases production of another crop. An example of
complementarity in cropping is the positive effect of one crop on the other crop.
Cordia alliodora and several Erythrina species are used as shade trees for coffee and cocoa. Trees
moderate the intensity of sunlight and wind, and maintain higher humidity. Crops under or
between the trees are protected from sudden changes in climate.
Species of Acacia, Leucaena, Gliricidia and other legumes are often interplanted with crops in
agroforestry systems, because the nitrogen fixed by these plants increases soil fertility and
benefits the crop plants.
Interplanting trees and crops as in the taungya system often results in a mutual benefit. Weeding
carried out by cultivators benefits both the crops and the trees in that it reduces competitions for
nutrients and water. The cut weeds represent a source of readily available nutrients to the crops
and trees, if used as a mulch. The crops and weeds, and their litter when they are cut provide a
mat over the soil which lessens erosion and reduces evaporation

2. SUPPLEMENTARY INTERACTION
This occurs if the presence of one crop does not influence the production of other crop(s). This is
an independent relationship. This relationship occurs if the different crops draw on resources at
different times of the year, or from different parts of the environment .e.g. different soil depth for
nutrients.
In taungya, crop plants occupy space between tree seedlings, and use light, nutrients and water
that presumably otherwise would be wasted. During the first growing season, tree seedlings are so
small that crops usually grow well despite their presence. The relationship between trees and
crops during the first year of taungya appears in most cases to be supplementary.
The next two types of interactions between trees and crops in agroforestry systems
are negative in nature; namely:

1. COMPETITION
The component plants in a mixed system compete for essential resources. Although agroforestry
is envisaged as a system of plant species that benefit each other mutually or unilaterally, it is too
optimistic to assume that all types of competition can be eliminated in these systems, especially in
areas with poor soils and scanty rainfall. Agroforestry systems lose some of the assimilated
nutrients in the form of grain, wood, fodder, etc, at each harvest, thus reducing reserves, unlike
natural forests where recycling of nutrients occurs.
Ideally, the relationship between crops and trees should be of a ‘complementary’ nature. However,
this is not always the case.
In many situations where trees and crops are grown together, they may compete for water,
nutrients and solar energy. The situation is obvious when the canopies of trees begin to close over
the tops of crops such as upland rice.
In Indonesian taungya (Tumpangsan) teak is often interplanted with giant Leucaena leucocephala
and with cassava as a cash crop. Leucaena leucocephala is beneficial in that it produces shade
and green manure. The side-shading results in good form for the teak. However, competition can
be deleterious when teak is enclosed by two rows of Leucaena leucocephala.
Competition between trees and crops is a long-term problem in plantations when the crop species
is a perennial.

2. ALLELOPATHY
Allelopathy is an interaction between plants or between plants and microorganisms in which
substances (allelochemicals) produced by one organism affect the growth of another (usually
adversely).
Allelopathy means plant-plant biochemical interactions that have detrimental effects, i. e. certain
plants release into the environment toxic chemicals that are injurious to other plant(s) in their
vicinity. Such toxic chemicals may be injurious to microbes and even to the seedlings of those
plants releasing them.

Chapter 4: NUTRIENT CYCLING IN TROPICALAGROFORESTRY SYSTEMS
4.1 NUTRIENT CYCLING — THE GENERAL CONCEPT
In a soil-plant system, plant nutrients are in a state of continuous, dynamic transfer. Plants take up
nutrients from the soil and use them for metabolic processes. In turn, plants return nutrients to
the soil either naturally as litterfall in unmanaged systems, deliberately as prunings
in some agroforestry systems, or through root senescence in both managed and
unmanaged systems. These plant parts are decomposed by soil microorganisms, releasing the
nutrients bound in them into the soil. The nutrients then become available for plant uptake once
again. The term Nutrient cycling, as used in most agroforestry discussions, refers to the
continuous transfer of nutrients that are already present within a soil-plant
system, such as a farmer’s field (Nair, 1993; Nair et al., 1995; Sanchez and Palm, 1996;
Buresh and Tian, 1997). However, in a broader sense, nutrient cycling involves the continuous
transfer of nutrients within and between different components of an ecosystem and includes
processes such as weathering of minerals, activities of soil biota, and other transformations
occurring in the biosphere, lithosphere, and hydrosphere (Jordan, 1985).

A generalized model of nutrient cycling in an ecosystem is presented in Figure 1 (DeAngelis,
1992). The model consists of a soil-plant-animal system partitioned into several compartments
(pools), with inputs into the system (gains), outputs from the system (losses), and
internal turnover or transfer within the system (cycling). Inputs into the system come
through fertilizer, rain, dust, organic materials from outside the system, N2 fixation, and
weathering of rocks. Outputs result from erosion, leaching, plant harvest, denitrification,
volatilization of N, and burning (Nair et al., 1995).
Nutrients entering the soil compartment contribute to the soil-nutrient pool. Water can remove
(leach) nutrients from the soil nutrient pool, with the level of nutrient loss determined by the flow
rate of the percolating water and the soil properties. Nutrients, such as nitrates, that dissolve
readily in water and are weakly held by the soil matrix have a greater likelihood of being leached
than do nutrients, such as phosphates, that have very low solubility and mobility in soils. On the
other hand, the loss of cations such as potassium depends on the exchange capacity of the soils.

FIGURE 1. General representation of energy and nutrient flows in an ecosystem. Dashed lines represent energy flows
and solid lines represent nutrient cycles and inputs and outputs. Outputs of nutrients include losses by water
transport of dissolved nutrients and drift or migration of living organisms. Source: DeAngelis (1992).
The autotroph (producer) component of an ecosystem (mostly plants) produces biomass
through photosynthesis, a process which also involves transpiration of water and uptake of
nutrients from the soil. Nutrients that are taken up are either stored within the plant or used in
the production of new biomass. Some of these nutrients are subsequently returned to the soil
through litter fall, root turnover, crown drip and stem flow. Decomposers in the soil mineralize
nutrients back to inorganic forms that can be used again by autotrophs, but also use available
nutrients, decreasing nutrient availability for autotrophs. Within-system movement of nutrients by
water, wind and organisms, as well as inputs to and losses from the ecosystem, are essential
processes (DeAngelis, 1992). Natural forest ecosystems of the tropics represent self-sustaining
and efficient nutrient cycling systems. These are “closed” nutrient cycling systems with relatively
little loss or gain of the actively cycling nutrients, and high rates of nutrient turnover within the
system. In contrast, most agricultural systems represent “open” or “leaky” systems with
comparatively high nutrient losses. Nutrient cycling in agroforestry systems falls between these
“extremes.” (Nair et al., 1995).

Figure 2, originally proposed by Nair (1984), presents a generalized model of nutrient cycling in an agroforestry
system, in comparison to cycling in monocrop agricultural and natural forest systems.
The figure emphasizes that the major difference between agroforestry and other agricultural
production systems is the greater possibility of managing the agroforestry system or its
components to facilitate increased rates of nutrient turnover or transfer within different
compartments of the system (Nair, 1993; Nair et al., 1995). In order to “exploit” these nutrient-
cycling advantages of agroforestry systems, we need to understand the processes involved.
Several reviews have addressed the topic .
Based on the current level of understanding, there appear to be three main tree-mediated processes
that determine nutrient cycling in tropical agroforestry systems: (1) increased input of N
through biological N2 fixation (BNF) by trees; (2) enhanced availability of
nutrients resulting from production and decomposition of substantial quantities
of tree biomass; (3) tree uptake of nutrients from deeper soil layers.

4.2. TREE-MEDIATED PROCESSES THAT AFFECT NUTRIENT
CYCLING IN AGROFORESTRY SYSTEMS
4.2.1 BIOLOGICAL NITROGEN FIXATION BY TREES
Both science and myth are involved in discussions on the role of BNF in nutrient cycling in
tropical agroforestry systems. The fact is that some trees that are, or potentially can be, used in
agroforestry systems have the ability to add N to the soil through BNF. The main myth concerns
the amount of N2 fixed by trees and shrubs and the extent to which it is actually used or
potentially available to the associated crop during various periods of time.
Among the 650 woody species belonging to nine families that are capable of fixing atmospheric
N2, 515 belong to the family Leguminosae (320 in Mimosoideae, 170 in Papilionoideae and 25 in
Caesalpinoideae). Several genera of nonleguminous N2-fixing trees (NFTs) are also important in
tropical agroforestry systems; examples include Alnus and Casuarina. Among some 120 genera of
NFTs (MacDicken, 1994), only a few are used directly as human food — fruits, flowers, leaves—
(examples include the genera Erythrina, Inga, Leucaena, Parkia, Pterocarpus, and Sesbania);
many are used for

timber, fuelwood, or fodder; and most, if not all, for soil improvement. This last aspect — soil
improvement — is achieved through several processes: (1) the direct contribution by trees to
the soil N pool through transfer of biologically fixed N, (2) increased nutrient turnover and
availability due to increased production and decomposition of biomass, and (3) improved
erosion control via appropriate tree planting arrangements and mulching with tree
prunings.
NFTs are a valuable resource in agroforestry systems. However, some of the widely held
assumptions about their benefits could be wrong or information about them may be inadequate.
Because of methodological difficulties in quantifying N2 fixation under field conditions,
especially in older tree-stands (Danso et al., 1992; Sanginga et al., 1996), quantitative information
on the extent of benefit that is actually realized by using NFTs in agroforestry systems is far from
satisfactory. Furthermore, it is not clearly understood what proportion of the N2 that is fixed by a
NFT is actually utilized by, or potentially made available to, an associated crop during the current
crop cycle, and what proportion goes into the soil’s N store for eventual use by subsequent crops.
If the N is transferred continuously from the NFT to the soil, the inclusion of the NFT should
enhance the soil N status in the long run. Obviously, rigorous, long-term monitoring of these
aspects is essential.

4.2.2 TREE BIOMASS AND ITS DECOMPOSITION
One of the major recognized avenues of soil fertility improvement in tropical agroforestry systems
is the recycling of nutrients through decomposition of tree biomass — mainly leaf litter or
prunings, but also roots— that is added to the soil. Obviously, the extent of benefits derived will
depend on the quantity and nutrient content of the biomass added, and the rate at which it is
decomposed. Voluminous information is available on the nutrient content and quantity of biomass
produced by different trees and shrubs used in agroforestry systems under a variety of conditions,
especially in systems such as alley cropping and improved fallows where soil fertility
improvement is a major objective. As is to be expected, considerable variation exists in such data.
Most reports on nutrient content of tree biomass deal with N; other elements such as P and K
are less commonly reported.

While trees in agroforestry systems may supply N to associated crops, their ability to supply P
is very limited. Many tropical soils have very low native P levels (Sanchez and Palm, 1996;
Buresh et al., 1997). Indeed, the low native soil P, high P fixation by soils with high iron and
aluminum contents, and the nutrient-depleting effects of long-term cropping without
additions of adequate external inputs have contributed to P deficiencies in many tropical
soils (Jama et al., 1997). Nevertheless, application of tree biomass to the soil has been shown to
increase crop available P especially in the highly weathered tropical soils. This is achieved either
directly by the process of decomposition and release of P from the biomass or indirectly by the
production of organic acids (by-products of decomposition) that chelate iron and aluminum,
reducing P fixation (Coleman et al., 1983; Nziguheba et al., 1998). However, as reported by Palm
(1995), the quantity of P contained in the biomass of most multipurpose tree species used in
agroforestry systems is insufficient to supply the associated crop’s P demand, though the biomass
may contain sufficient N to meet the immediate crop N requirements. Jama et al. (1997)
concluded that it could be economically attractive to integrate an inorganic P source with the
organic material, whereby the organic material would provide the required N for the crop and the
inorganic P source would meet the additional requirement of P.

Decomposition of organic materials and the rate at which their nutrients are released are
determined by the “quality” of the material, the environment, and the decomposer
organisms that are present (Swift et al., 1979). Since many recent studies have focused on the
quality of plant biomass available in agroforestry systems, a discussion on the current status of
this topic will be useful.
4.2.3 TREE UPTAKE OF NUTRIENTS FROM DEEPER SOIL LAYERS
Trees have deep and spreading roots and hence are capable of taking up nutrients and water
from deeper soil layers usually where herbaceous crop roots cannot reach. This process of
taking up nutrients from deeper soil profile and eventually depositing on the surface layers
through litter-fall and other mechanisms is referred to as 'nutrient pumping' by trees. This
process is mainly depends on characteristics of tree species and other soil, climatic and
topographic factors. Recent research on agroforestry trees has focused on this
deep-rooting attribute of trees, with a view to understanding the spatial distribution and temporal
patterns of root growth (Jonsson et al., 1988; Ruhigwa et al 1992; van Noordwijk et al., 1996) and
relating such information to nutrient uptake by tree roots from deeper soil layers (Mekonnen et al.,
1997; Buresh and Tian, 1997). Reviewing the current level of knowledge in this area of research,
Buresh and Tian (1997) concluded that the potential of trees to take up subsoil nutrients is
generally greatest when the trees have

deep root systems and a high demand for nutrients, and when they are grown in locations with
water and/or nutrient stress in the surface soil but considerable reserves of plant-available
nutrients or weatherable minerals in the subsoil. Trees of low moisture content soils have
deep root systems and helps in nutrient and water pumping as compared to
high moisture soils (Makumba et al., 2009; Schroth and Sinclair, 2003;
Schroth, 1999).The potential for nutrient uptake from deeper soils is much greater for
water soluble nutrients such as nitrate than for immobile nutrients such as P. There is
typically little potential for trees to take up and recycle P from below the rooting depth of
annual crops because plant extractable P is normally low in subsoil and the phosphate ion is
relatively immobile in soil (Buresh and Tian, 1997). The role of trees in nutrient uptake from
deeper soil layers for nutrients other than N and P is, in general, little studied.Soil physical
and chemical barriers to rooting will reduce the potential of trees to retrieve and take up subsoil
nutrients. Mobile nutrients in acid soils of the humid tropics can be leached by high rains into
subsoil where high aluminum saturation restricts the rooting of crops. In such systems, the roots
of trees with a horizontal spread in the subsoil may act as a “safety net,” which intercepts nutrients
as they leach down the soil profile (van Noordwijk et al., 1996).In semiarid areas, the lateral
extension of tree roots is considered to be more important in nutrient uptake than the penetration
of roots to deeper soil horizons (Breman and Kessler, 1995). 1997)

CHAPTER 5: BENEFITS AND CHALLENGES RELATED TO
Benefits of agroforestry systems
Environment Benefits: Combining trees with food crops on cropland farms yield certain
important environment benefits, both general ecological benefits and specific on-site benefits.
The general ecological benefits include:
 Reduction of pressure on forest
 More efficient recycling of nutrients by deep-rooted trees on the site.
 Better protection of ecological systems.
 Reduction of surface run-off, nutrient leaching and soil erosion through impending effect of
tree roots and stems of these processes.
 Improvement of microclimate, such as lowering of soil surface temperature and reduction of
evaporation of soil moisture through a combination of mulching and shading.
 Increment in nutrients through addition and decomposition of litter-fall.
 Improvement of soil structure through the constant addition of organic matter from
decomposed litter.


Economic Benefits: Agroforestry systems on croplands/farmlands bring significant economic
benefits to the farmer, the community, the region or the nation. Such benefits may include:
 Increment in an maintenance of outputs of food, fuelwood, fodder, timber
 Reduction in incidence of total crop failure, common to single-cropping or monoculture
system
 Increase in levels of farm incomes due to improved and sustained productivity.
Social Benefits: Besides the economic benefits, social benefits occur from increase in crop and
tree product yields and in the sustainability of these products. These benefits include:
 Improvement in rural living standards from sustained employment and higher incomes
 Improvement in nutrition and health due to increased quality and diversity of food outputs
 Stabilization and improvement of upland communities through elimination of the need to shift
sites of farm activities.
Limitations of Agroforestry
An integrated food-tree farming system, while advantageous, does have certain negative aspects.

Environment Aspects:
(i) possible competition of trees with food crops for space, sunlight, moisture and nutrients which
may reduce food crop yield;
(ii) damage to food crop during tree harvest operation;
(iii) potential of trees to serve as hosts to insect pests that are harmful to food crops; and
(iv) rapid regeneration by prolific trees, which may displace food crops and take over entire fields.
Socioeconomic Aspects:
(i) Requirement for more labour inputs, which may causes scarcity at times in other farm
activities;
(ii) Competition between food and tree crops, which could cause aggregate yields to be lower than
those of a single crop;
(iii) Longer period required for trees to grow to maturity and acquire an economic value;
(iv) Resistance by farmers to displace food crops with trees, especially where land is scarce; and
(i) The fact that agroforestry is more complex, less well understood and more difficult to apply,
compared to single-crop farm.

Through skilful management practices, any or all these aspects can be controlled. For example, it
is easy to adopt some or all of the following strategies:
(i) Select legume trees that have small or light crowns so that sufficient sunlight will reach the
food crop for photosynthesis;
(ii) Select tree species that are deep-rooted so that they will absorb moisture and nutrias from the
surface layer of the soil; and
(iii) Space the trees farther apart to reduce their competitive effects on the food crops.

Sample questions:
I. Definitions (revise possible definitions)
II. Classify agroforestry according to:
A) The function with examples
b) Socioeconomics with examples
III Explain different components of any agroforestry systems
IV Explain different types of (positive or negative) interactions
V Explain the benefits/ limitations of agroforestry

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