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AGI5373 Agroforestry Session 1: An Introduction to Agroforestry Session 1 An introduction to Agroforestry Content Introduction 1 1.1 What is agroforestry 1 1.2 Historical background of agroforestry 3 1.3 Transforming into modern agroforestry 4 1.4 Classification of agroforestry systems 5 1.5 Benefits of agroforestry 8 1.5.1 Social benefits 8 1.5.2 Environmental benefits 9 1.5.3 Economic benefits 10 1.6 Limitations of agroforestry 11 Summary 12 Learning outcome 12 Introduction There are lots of definitions for agroforestry. Simply it is planting trees with crops and livestock. However the definition given by the ICRAF’s ( International Council for Research in Agroforestry) is more meaning full. This is not a new practice of land use. The history of the agroforestry goes back to centuries. However the word agroforestry coined in late 1970s. Establishment of International Council for Research in Agroforestry in 1978 ( present World Agroforestry Centre) is a turning point of the development of agroforestry from its traditional system to modern system. There are three types of agroforestry systems namely Agrisilvicultural system, Silvopastoral systems and Agrosylvopastoral system. There are social, environmental and economic benefits in this sustainable land use system. Also there are limitations in these systems. 1.1 What is agroforestry First, we will try to understand what agroforestry is? or to define the term agroforestry. Very simply agroforestry (agriculture + forestry) is a system of cultivation that merges the two land use patterns of agriculture and forestry. Now let us see what is agriculture? and what is forestry? 1 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry Agriculture is the practice of growing crops and/or raising animals to produce food, fiber, wool and sometime for farm power. Forestry is the science and craft of creating, managing, using, conserving, and repairing forests, woodlands, and associated resources for human and environmental benefits. A forest is a large area dominated by trees. Therefore now we can define agroforestry as integration of trees, crops and/or livestock on the same plot of land. In other word cultivation and use of trees and shrubs with crops and livestock in agricultural systems. However this land use system is not that much simple. The simplest agroforestry system is more complex than a monocrop. There are lots of ecological and economical interactions take place between different components of this system. As a result of these interactions the system provide enhanced resiliency and a more productive and profitable use of the land compared to a monoculture system. It manages natural resource such as soil, water etc. The multifunctional system provides increased social, economic and environmental benefits for land users at all levels. The system is crucial for smallholder farmers and rural people because it enhance the food availability, income of rural society and health. It is a dynamic system having ecological base. Now you can realize the definition given above is too simple. Because of the complexity of the system different definitions are appeared in different articles. According to Nair, 1989 agroforestry has been defined in several ways. Few definitions are given below.  Agroforestry, cultivation and use of trees and shrubs with crops and livestock in agricultural systems.  Agroforestry is the management and integration of trees, crops and/or livestock on the same plot of land and can be an integral component of productive agriculture.  Agroforestry is an activity that combines production on the same plot of land, from annual agricultural activities (such as crops and pasture) and from delayed long-term production by trees (for example timber and services).  Agroforestry is a cultivation system that merges trees and agriculture (crops or livestock), providing enhanced resiliency and a more productive and profitable use of the land compared to a monoculture system.  Agroforestry is a collective name for land-use systems and technologies where woody perennials (trees, shrubs, palms, bamboos, etc.) are deliberately used on the same land-management units as agricultural crops and/or animals, in some form of spatial arrangement or temporal sequence. 2 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry  Agroforestry can also be defined as a dynamic, ecologically based, natural resource management system that, through the integration of trees on farms and in the agricultural landscape, diversifies and sustains production for increased social, economic and environmental benefits for land users at all levels.  ICRAF’s ( International Council for Research in Agroforestry) current definition is a collective name for land-use systems and practices in which woody perennials are deliberately integrated with crops and/or animals on the same land management unit. The integration can be either in a spatial mixture or in a temporal sequence. There are normally both ecological and economic interactions between the woody and non-woody components in agroforestry. What are common to all these definitions: i.e. The particular land use system consists of trees and crops and/or livestock, there are both ecological and economic interactions between the woody and non-woody components, sustainable system having social, economic and environmental benefits. According to Sanchez, 1995 the definition given by the ICRAF’s has served well and helped agroforestry to become recognized as a branch of agricultural science. SAQ. 1 What are the major components of agroforestry systems? 1.2 Historical background of agroforestry Agroforestry is not a new practice. it has been utilized all over the world for many years particularly in developing countries. The practice of cultivation of trees with agricultural crops and/or livestock or integrating trees in the agricultural landscape has existed from ancient times around the world until monocropping became more common, in an effort to intensify food production. Early 20th century J. Russell Smith an American economic geographer in his book Tree Crops: A Permanent Agriculture (1929), agroforestry was formally outlined. He stressed tree-based agriculture as a solution to the destructive erosion. However with the green revolution in late 1960s this valuable system was largely overlooked and needs of the rural farming community was neglected. In 1977, the important role of trees in sustaining agricultural production in the tropics was highlighted in the report called Trees, Food and People (part 3 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry of the Project for Identification of Tropical Forestry Research Priorities) released by the Canadian International Development Research Centre. As a result of the visionary study in the mid-1970s led by forester John Bene of this project action had been taken to establish the International Council for Research in Agroforestry (ICRAF) in 1978 to promote agroforestry research in developing countries. With the establishment of ICRAF lots of study and research on agroforestry were carried out worldwide. And the key role of trees play on farm was well recognized. In year 2002 - ICRAF becomes the World Agroforestry Centre. Late 1970s the international development community paid much attention to the negative effects of green revolution on society, environment and deprived farming communities. As a result of this revisit on high input agriculture, they recognized agroforestry as one of the sustainable land use patterns. The historical background of agroforestry in Sri Lanka will be discussed in session 8 of this unit. 1.3 Transforming into modern agroforestry The term “agroforestry” was coined in the late 1970s giving much recognition to the agroforestry. This is the period where the global community paid more attention to the negative effects of green revolution on society and environment due to high input agriculture. Same time the world community rethink about the deprived poor farmers. They gained more attention from the international development community. With the establishment of ICRAF, agroforestry had been recognized as an benificial land use practice deserving intensified research. Therefore they conducted strategic research on agroforestry throughout the tropics with the aim of poverty reduction, increasing food security, minimize environmental problems and find alternatives to slash and burn agriculture. The government of Philippines was among the first to support agroforestry as a sustainable land use pattern which can be used as a viable strategy for rural development. In 2014, the government of India adopted a National Agroforestry Policy. With this intervention most of the developing countries paid much attention to adoption of agroforestry. Having identified the benefits of agroforestry, developed countries too extended their support for the development of this valuable land use pattern. There are lots of examples for this all over the world. Few of them are as follow;  In the United States, the USDA Interagency Working Group on Agroforestry in 1996 took on the issue of institutionalization. Its work and subsequent follow-up reports led to the adoption of the 2011-2016 Strategic Framework, which seeks to (1) increase use of agroforestry by landowners and communities, (2) advance the understanding of, 4 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry and tools for, applying agroforestry and (3) incorporate agroforestry into an all-lands approach to conservation and economic development.  In 2001, in Europe, tree-based intercropping systems were accepted for access to funding support from the Common Agricultural Policy (CAP) of the European Union. In 2004, the European Commission launched Article 44 for support to agroforestry. In the new CAP of 2014, agroforestry is seen as a solution to enhance biodiversity on farms and also as a mean to improve forest areas and rural development. It therefore provides funding for establishment and maintenance agroforestry practices to this effect.  Australia and New Zealand are also recognizing the diverse benefits of agroforestry, or farm forestry. Through their respective programs, Land care and the Sustainable Farming Fund, growing trees on farms is seen as a way to gear agricultural practices towards a more sustainable path, notably with agroforestry projects. 1.4 Classification of agroforestry systems There are lots of agroforestry systems all over the world. There are similarities among the systems and dissimilarities. For an example in some systems only trees and crops are present where as in some other system animal and/or pasture are present in addition to the trees and crop. Therefore with the modernization of agroforestry the requirement of a classification of the systems become important. Further this type of classification is useful to provide a framework for evaluating different systems, for the improvement of systems and for research purposes. The data on existing agroforestry systems and practices from different parts of the tropics and subtropics appeared in the Agroforestry Systems Inventory (AFSI) of ICRAF provided strong basis for the classification of agroforestry systems. Accordingly several criteria were used to classify agroforestry systems and practices. Those are; 1. Structure of the system (structural basis). Here the composition and arrangement of components within the system were considered. Arrangement of components can be in time (temporal arrangement of the various components) or space (specially the spatial arrangement and vertical stratification of woody components) 2. Functional basis Major function of the system (main output and role of mainly in the woody components) were considered. These functions can be either productive, e.g. production of food, fodder, fuelwood etc. or protective e.g. windbreak, shelterbelt, soil conservation and fertility improvement etc. 5 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry 3. Ecological basis Refers to the environmental condition and ecological suitability of the systems. Some types of systems are common in certain ecological conditions such as lowland humid tropics, arid and semi-arid tropics, tropical highlands etc. 4. Socio-economic basis Refers to the level of inputs of management (low-input) or intensity or scale of management and commercial goals to designate systems as commercial, intermediate, or subsistence. However the structural basis of the system used to classify the systems at the primary step in classification since there are only three basic sets of components that are managed by man in all systems i.e. woody perennials (trees), herbaceous plants (crops) and animals. These components can be combined in many spatial and temporal arrangements and for different functions, creating many different kinds of systems. Accordingly there are three major types of agroforestry systems can be found as follow. 1. Agrisilvicultural system (crops + trees) Agricultural crops and trees are the component of this system (i.e. combination of crops and trees). e.g. alley cropping, home gardens (figure 1.1) 2. Silvopastoral systems (trees + pasture/animals) Trees and domesticated animals on pastures are the components of the system (i.e. combination of forestry and grazing of domesticated animals on pastures). e.g. rangelands rangelands or on-farm. No crops in this system (figure1.2) 3. Agrosylvopastoral system (trees + pasture/animals + crops) Trees, pasture/animals and crops are the components. e.g. home gardens involving animals, scattered trees on croplands used for grazing after harvests (figure 1.3). 6 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry (a) (b) Figure 1.1 Agrisilvicultural system (a) home garden (b) alley cropping Figure 1.2 Silvopastoral system Figure 1.3 Agrosylvopastoral system 7 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry In addition there are two specialized systems called; 1. Entomoforestry - trees with insects e.g. honey bees or silk moths 2.Aquaforestry – trees (mangroves) with fish. e.g. mangroves or trees round ponds so leaf litter enriches the water for fish production). However in this session we are not going to discuss these systems further since more details on the systems are appeared in unit 2 SAQ. 2 Differentiate three major types of agroforestry systems from each other. 1.5 Benefits of agroforestry Now you all have a very basic idea on agroforestry I suppose. With this knowledge we will try to understand the benefits of agroforestry systems. Benefits of agroforestry systems are countless since the systems are multifunctional. Therefore they can provide range of economic, sociocultural, and environmental benefits. However for the convenience of the study we can categories all these benefits into few main categories as follow. 1. Social benefits. 2. Environmental benefits. 3. Economic benefits. It is impossible to describe all the benefits in this type of session. Therefore we will try to understand most important benefits. 1.5.1 Social benefits. i. Increased food availability/food security As you aware the world population is increasing. Provision of food for the ever growing population is a global challenge. Resource limitation specially the arable land aggravates the problem. Mmillions of people still suffering from hunger globally. In addition to finding solution for the hungry living, to meet the demand for food by 2050, production will have to increase by over 60% (Food and Agricultural Organization (FAO) of United Nations (UN). More sustainable farming practices are necessary to overcome these problems. 8 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry Agroforestry is one of the solutions for this since we can use the interaction between trees, crops, pasture and livestock to increase food production. Ability to produce variety of food such as egg, milk, meat (through animals), fruits, nuts, and leaves (through trees) and vegetables (through crops) within a same land plot provide more balance, nutritious and healthy food for human being. Can increase the land use efficiency and subsequent productivity of food since all trees, crops and animals are in the given area of land. Increased food availability decreases the hunger as well as malnutrition. ii. Reduced malnutrition in the society Increased food availability and variety of food ensure well-nourished balance and healthy diet which help eradicate hunger and malnutrition. iii. Improved rural living standards Increased and diverse income of the farmers improves their purchasing power. Food availability improve the health conditions of individuals. This will help to keep their living standards in a better place. iv. Women empowerment Agroforestry can improve gender equality by empowering women. Women headed households in rural farm families. They are responsible for cooking, looked after their children, gathering firewood which are not easy tasks. Agroforestry can make easier these tasks. For an example firewood, some food or fodder can access closely and easily by women in an agroforestry system which saves her time. Further women have the chance to sell food, fruits, fodder or firewood in the vicinity of the system and thus access to cash. v. Recreation Structure of agroforestry systems are near to a natural forest. This will help for the recreation. 1.5.2 Environmental benefits i. Mitigation of climate change and adaptation Wood products of the agroforestry systems decrees the pressure on forest products i.e. reduced rate of deforestation one of the major reasons for climate change. Integrating trees in agricultural systems help to minimize carbon dioxide level in the atmosphere through carbon sequestration. Can meet energy requirement in a carbon neutral way using fuel wood. Shade and a cooler environment in the system can prevent crops and animals from the impact of climate change where as can minimize contribution of agriculture to the climate change by minimizing pressure on natural forests for forest 9 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry products. Improved soil nutrient conditions minimize the use of chemical fertilizer recognized as one of the greenhouse gas sources. ii. Protect natural resources The better land cover of the systems prevents run off and subsequent soil erosion. The land cover helpful to recharge ground water resource through increased infiltration. Minimal runoff prevents pollution of water bodies i.e. sedimentation, nutrient and waste accumulation. Proper nutrient cycling in the system, nitrogen fixation if legumes included minimize the use of chemical fertilizer and thus soil pollution. It improves the water quality by filtering and capturing of water resources properly through trees. iii. Pest control Natural equilibrium of the system controls the populations of insects. It helps to keep insect pest populations below the economic injury level. Further the trees provide shelter to natural enemies. iv. Prevents environmental hazards Especially due to the trees reduce the vulnerability to environmental hazards like flood, drought and cyclones. Root systems of the trees stabilize the soil structures. Large canopies of the trees reduce the velocity of rain water fell on the soil. These factors minimize the erosion and the risk of landslides. Trees act as windbreaks and help prevent animals and crops from strong winds as well as wind erosion. Water conservation of trees minimize the effect of drought. Increased and diverse production of the systems improve the recovery of people after natural hazards. v. Conservation of bio diversity Presence of trees, crops, animals and their different varieties increases the biodiversity. Further the trees provide shelter for various plants, animals and insects. The soil provides living space for different organisms. 1.5.3 Economic benefits i. Increased income and poverty alleviation Increased as well as diverse production ensure the increased income of farm family. Minimal inputs for the system save the money of farmers. It also reduces production cost. Therefore the reduced unit price of products creates more demand for such commodities which increases the farm income. 10 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry ii. Increased market opportunities There are market opportunities for valuable forest products. iii. Reduced risk of economic failures Diversity of products reduces the risk of economic failures. However we can’t expect all the benefits above from each and every agroforestry system. It depends on the number of components in the system, aim of the farmer, management practices, etc. SAQ. 3 What are the three major categories of benefits of agroforestry systems? 1.6 Limitations in agroforestry Though there are lots of benefits in agroforestry it also faces for many limitations. Some of them are as follow; 1. Delayed return It will take number of years to get the net return especially from some tree species. Therefore the breakeven point for some agroforestry systems get delayed for number of years. 2. Marketing problems No proper value chain for tree related products. 3. Lack of incentives and policy on agroforestry No clear policy on agroforestry due to lack of attention of the authorities. No incentives, credit facilities or any other institutional support for agroforestry. 4. Lack of awareness Lack of awareness from top to bottom i.e. from policy makers to farmer on benefit of this sustainable land management system. 5. Contradictions with regulations Especially the forest regulations discourage the investment on the system. For an example forest regulation preclude tree growing on farms by restricting the harvesting, cutting or selling of tree products. 11 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry 6. Lack of coordination Poor coordination among the relevant sectors or institutions such as agriculture, forestry, livestock, rural development, environment, energy etc. create policy conflicts and omissions. Summary Simply the agroforestry is planting trees with crops and livestock. This is a centuries old practice but the term agroforestry was coined in late 1970s. Establishment of International Council for Research in Agroforestry in 1978 ( present World Agroforestry Centre) is a turning point of the development of agroforestry. There are three types of agroforestry systems.There are social, environmental and economic benefits in this sustainable land use system. Also there are limitations in these systems. Learning outcomes After going through this session the students should be able to;  Define agroforestry  Explain the transformation of agroforestry with time  Identify three types of agroforestry systems and their benefits  Identify limitations of agroforestry Answers for the SAQs: SAQ.1 Trees, crops and livestock/pasture SAQ. 2 Agrisilvicultural system – consists of crops and trees Silvopastoral systems – consists of trees and pasture/animals Agrosylvopastoral system consists of trees, pasture/animals and crops SAQ. 3 Social benefits Environment benefits Economic benefits Recommended reference 12 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 1: An Introduction to Agroforestry P.K. Ramachandran Nair, An Introduction to agroforestry, Section 1 and 11 13 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system Session 2 Distribution of agroforestry system Content Introduction 13 2.1 World’s ecological zones 14 2.2 Importance of the study of distribution 15 2.3 Agroforestry in the world – historical distribution 15 2.4 Agroforestry in the world – Current status 15 2.5 Agroforestry systems in tropics 17 2.6 Agroforestry systems in temperate zone 19 2.7 Factors which determine the existence of an agroforestry system 21 Summary 21 Learning outcome 22 Introduction Ecological factors primarily determine the biomass distribution of all over the globe. An agroforestry system is a biomass. Therefore, ecological factors determine the distribution of agroforestry system all over the world. The agroforestry systems are distributed in ecological zones in the world accordingly. Study of distribution of agroforestry systems is important in livelihood development of farming communities, global agricultural production and environment. Further the study of the distribution and quantification of the extent under agroforestry is important for the personnel involved in agricultural production, planning and policy development. Agroforestry is an ancient practice adopted by the farmers mainly in tropics as well as temperate zone. With the establishment of International Council for Research in Agroforestry (ICRAF) in 1977, the ancient practice of land use pattern was institutionalized and named it as agroforestry. Hard work of ICRAF added more value to the agroforestry. Based on the data gathered by ICRAF for the preparation of Agroforestry Systems Inventory AFSI, the existing agroforestry systems have been classified into three major types based on their structure. These are Agrosilvicultural system (crops + trees), Silvopastoral system (trees and pasture/animals) and Agrosilvipastoral system (crops + pasture/animals + trees). Existence of an agroforestry system in a particular region decide by the environmental and agroecological factors, socio-economic considerations and functional aspects. Copyright © 2019, The Open University of Sri Lanka 13 AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system 2.1 World’s ecological zones Before we discuss the distribution of agroforestry systems, we will try to get a basic idea on ecological zones of the world. Because ecological factors primarily determine the biomass distribution all over the globe (ecological factors are biotic or abiotic factors that influence living organisms such as climate, steepness and sunlight on vegetation, direction of slope, soil, interrelationships among different organisms). Therefore the world’s biomass is not evenly distributed. This is true for agroforestry systems too since an agroforestry system can be considered as a biomass. In other word ecological factors determined the existence or adoption of an agroforestry system in a particular area or an ecological zone. An Ecological Zone (EZ) is defined as, a zone or area with broad yet relatively homogeneous natural vegetation formations, similar (not necessarily identical) in physiognomy. Boundaries of the EZs approximately coincide with the map of Köppen-Trewartha climatic types, which was based on temperature and rainfall. An exception to this definition is “Mountain systems”, classified as one separate EZ in each Domain and characterized by a high variation in both vegetation formations and climatic conditions caused by large altitude and topographic variation” (Simons, 2001). There are five major ecological zones (domains) in the world, namely Tropical, Subtropical, Temperate, Boreal and Polar. There are sub zones under each domain except Polar (figure 2.1). The ecological zones divide the globe into five major ecologically valid units for global forest reporting (we will discuss the different agroforestry systems and practices distributed among the ecological zones later). Source: Forest resources Assessment Working Paper 179 of FAO Figure 2.1 The 2010 global ecological zone map 14 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system 2.2 Importance of the study of distribution Agroforestry is a kind of land use that has been practiced since long in many parts of the world (Regmi and Garforth). However the type and composition and extent vary from place to place because of varied topography, biophysical attributes and socioeconomics (Singh et al.,). The importance and role of agroforestry both to the livelihood of farming communities as well as total global agricultural production can be assessed by understanding the extent and distribution of trees on agricultural land, at the landscape level, including the numbers and characteristics of farmers and farming communities within those landscapes. Further to assess the environmental services or the protective functions of agroforestry the distribution is important. Study of the distribution and quantification of the extent under agroforestry is important for the personnel involved in agricultural production, planning and policy development. 2.3 Agroforestry in the world – historical distribution This land use pattern is an ancient practice adopted by the farmers mainly in tropics as well as temperate zone. For an example, King (1987) stated that the slash and burnt cultivation was a common practice of farmers in Europe until middle ages. Shifting cultivation in Sri Lanka, Hanunoo farming system in Philippines were few examples in the Asian region. In both of these systems, when clearing the forest for cultivation of agricultural crops deliberately kept some trees scattered all over the field. According to Forde (1937), yams, maize, pumpkins, and beans were cultivated simultaneously under trees southern Nigeria, in Africa. The Taungya system of planting Teak initiated by Myanmar in late nineteenth century spread to South Africa and India later. An interesting feature of this system was the laborers who worked in these teak plantations were allowed to grow agricultural crops in between teak rows at seedling stage (we will discuss this system Taungya at later stage of this course). So it is clear, this system of land use practice has adopted by the farmers of all over the world from ancient time. 2.4 Agroforestry in the world – Current status Nowadays, intentional inclusion of woody perennials into crop farms (trees on farms) is a widespread practice all over the world especially in tropics. These systems vary from Agrosylvopastoral systems, home gardens, alley intercropping, biomass plantations to shifting cultivation across the world. With the initiatives taken by the world, the spread of agroforestry practices all over the globe has increased. For an example the establishment of International Council for Research in Agroforestry (ICRAF) in 1977, the ancient practice of land use pattern was institutionalized and named it as agroforestry. In 1991 the ICRAF renamed as International Centre for Research in Agroforestry (ICRAF). Note that the word “Council” in previous name changed into “Centre.” Hard work of ICRAF added more value to the agroforestry. Further it was able to draw global attention to this sustainable land use system through conducting research, disseminating knowledge and Copyright © 2019, The Open University of Sri Lanka 15 AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system gathering worldwide information on this valuable practice. With all these initiatives the land under agroforestry across the world has risen up. According to World bank (2004), 1.2 billion rural people currently practice agroforestry on their farms and in their communities and depend upon its products. According to Nair and Garrity (2012), the number of trees on farms is increasing the world over. About one billion hectares of agricultural landscapes already have more than 10% tree cover and a total of 1.6 billion hectares around the globe has the potential to become under agroforestry in near future. Further they pointed out a substantial increase of trees on croplands, or what we now call Ever Green Agriculture going to be an inevitable phenomenon in the future and the future of trees (and forests) is on farms. Let us move to see the results of a global assessment on agroforestry carried out by Zomer et.al. in 2009 and published in 2014 in working paper 179 of FAO, titled Trees on farms: an update and reanalysis of agroforestry’s global extent and socio-ecological characteristics. By, Robert J. Zomer, Antonio Trabucco, Richard Coe, Frank Place, Meine van Noordwijk and Jianchu Xu In 2009, World Agroforestry Center (early ICRAF) first attempted to quantify the extent of global agroforestry. This attempt was made to address the problem of broadly varying estimates. The above study was an outcome of this effort taken by World Agroforestry Center. This is how Zomer et.al. summarized their findings in the abstract of above said working paper. Among the key results are that, 1) agroforestry appears to increase globally both in extent and in number of people associated with it; 2) remains a significant feature of agriculture in all regions; 3) that its extent varies significantly across different regions (for example, more widespread in Central America and less in East Asia); 4) that tree cover is strongly positively related to humidity; and that 5) there are mixed relationships between tree cover and population density depending on the region. Agroforestry, if defined by tree cover on agricultural land of greater than 10%, is widespread: found on more that 43% of all agricultural land globally, where 30% of rural populations live. 16 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system Elaborating the results further they have pointed out following, Based on our current analysis, this land-use type represents over 1 billion hectares of land and more than 900 million people. Agroforestry is particularly prevalent in Southeast Asia, Central America, and South America with over 50% of area under agroforestry. Globally, the amount of tree cover on agricultural land increased substantially in the decade under investigation, with the area of >10% tree cover increasing 3%, or more than 828 000 km². South America showed the largest increase in area with >10% tree cover: more than 489 000 km² :an increase of 12.6%. South Asia also showed a large increase (6.7%), along with East Asia (5%), Oceania (3.2%) and Southeast Asia (2.7%). In Central America, the area with >10% tree cover increased by 1.6% to become 96% of all agricultural land. For Sub-Saharan Africa, we found an increase of 2%. Only Northern and Central Asia showed a decrease: - 2.9%. Tree cover apparently is still on the increase as a common feature on agricultural land throughout the world. It is essential that this is recognized by all involved in agricultural production, planning and policy development. SAQ. 1 What is the importance of study of the distribution of agroforestry systems? 2.5 Agroforestry systems in tropics The Agroforestry Systems Inventory (AFSI) on existing agroforestry systems and practices prepared by ICRAF is useful in finding the distribution of agroforestry systems in tropics and subtropics. Having evaluate the data gathered for the preparation of AFSI, the existing agroforestry systems have been classified into three major types based on their structure. These are; 1. Agrosilvicultural system (crops + trees) 2. Silvopastoral system (trees and pasture/animals) 3. Agrosilvipastoral system (crops + pasture/animals + trees). Each of the above major types of agroforestry systems consists of several agroforestry practices. The agroforestry practices come under each major types of agroforestry systems are as follow; Agrosilvicultural systems: improved fallow, Taungya, alley cropping/hedgerow intercropping, multilayer tree gardens, Multipurpose trees on cropland, plantation crop combinations, home gardens, trees in soil conservation and reclamation, shelter belts and wind breaks, live hedges, fuel wood production. Silvipastoral system: trees on rangeland or pasture, protein bank, plantation crops with pasture and animals. Agrosilvipastoral system: home gardens involving animals, multipurpose woody hedge rows. Other systems: apiculture with trees, aqua forestry, multipurpose wood lots. Copyright © 2019, The Open University of Sri Lanka 17 AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system Adoption of an agroforestry system to a particular locality primarily determined by the ecological factors of that locality. In tropics ecology of particular locality is determined by rain fall (both quantity and distribution throughout the year), temperature and altitude (altitude influence on temperature). These two climatic factors and altitude determine the existence of an agroforestry system in particular ecological zone. If the components of an agroforestry system can adopt to these conditions in a region such system can survive in that locality. Therefore some agroforestry systems can be found only in particular ecological zone or they are characteristics to the major ecological zones (table 2.1). Table 2.1 Characteristic agroforestry systems in few ecological zones Ecological zone Characteristic agroforestry systems Humid/sub humid Home gardens lowland Plantation crop combinations Multilayer tree gardens Alley cropping and other intercropping systems Semi-arid/arid Silvopastoral systems lands Wind break/shelter belts MPTs for fuel/fodder MPTs on farmlands Highlands Soil conservation hedges Silvopastoral combinations Plantation crop systems Though some systems can be found in all ecological zones the nature of their components vary from zone to zone depending on the ecological factors (ecological regions recognized in the State of Food and Agriculture Reports (SOFA) of FAO are more relevant in agroforestry). Those are temperate, Mediterranean, arid and semi-arid, sub-humid tropical (lowland), humid tropical (lowland) and highland regions. However, the later four regions represent the tropical and subtropical zones. Major ecological regions of tropics and sub tropics are shown in figure 2.2 below. 18 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system Figure 2.2 Major ecological regions of tropics and sub tropics The hot, humid climates in lowland humid and sub-humid tropics (humid tropics) prevailed throughout the year favor the growth of evergreen or semi- evergreen vegetation. Further it supports rapid growth of variety of species. Home gardens, plantation crop combinations, multilayer tree gardens, trees on rangelands and pastures, other Silvopastoral systems, improved fallow in shifting cultivation, multipurpose tree woodlots can be found in the region. There are one or two wet seasons and one long dry season in semi-arid and arid tropics. Home gardens, multilayer tree gardens, Silvopastoral systems, windbreaks and shelterbelts, multipurpose trees on crop lands are the prominent agroforestry systems. Land in the tropics having elevations from 900 to 1800 m are highlands. Soil erosion is a major problem in this region due to sloping lands and steep terrains. Low temperature influences the growth of lowland tropical species. The agroforestry systems can be found are plantation crops, woody perennials for soil conservation and fertility maintenance, improved fallows and Silvopastoral combinations. 2.6 Agroforestry systems in temperate zone Though we pay much attention to the agroforestry in tropics and subtropics it is essential to explore the possibility of improving the agroforestry in temperate zone too. Favorable agroclimatic factors prevailing in tropics and sub tropics for the growth and development of variety of species, widespread traditional agroforestry systems in the region and the potential of agroforestry to solve characteristic land use problems and socioeconomic problems of developing countries in the region attracted relevant parties from farmers to researchers to pay much attention on this region. Copyright © 2019, The Open University of Sri Lanka 19 AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system As in tropics the history of temperate agroforestry too goes back to many more years. Go through the following examples; 1. J. Russell Smith an economic geographer at Columbia University in 1909 first pointed out the importance of doing agriculture based on trees in United State. In 1914 he encouraged interplanting crop trees with woody legumes combined with animals in a given area to maximize the benefits. 2. New Zealand is the first developed country test the idea of integration of agriculture and forestry. The concept of “farm forestry” introduced to solve the conflict over usage of land for agriculture and forestry. 3. In Italy tillage and intercropping Maize (in first year), legumes and grain (rest of the three years) during first four years with poplar stands was a success story. 4.In northern China hybrid poplar intercropped with sesame, soya bean, peanuts, and cotton during first two to three years given more benefits to the growers. Seasonality of temperate region i.e. presence of distinct warm and cold seasons restricts the cultivation of same crop throughout the year. The variety of systems and practices are less. Agrisilvicultural practices (windbreaks and shelterbelt to prevent erosion) and Silvopastoral systems (animals in woodlands and rangelands) are the common systems. Socioeconomic factors too influence the agroforestry in the region. The large scale farms with high level of mechanization produce one or two high value crops for local or distant market. Inclusion of trees in such farms are basically to economic profit. However the ever growing fuel cost for highly mechanized farming practices, environmental pollution due to burning fossil fuels, soil erosion, farm surplus, forestry sector problems like high cost of establishment, late return and risk of fire put a pressure on land owners to rethink about their farming practices. So they think about the requirement of less energy intensive farming practices, soil conservation and fertility improvement and more efficient and diversified farming systems and found agroforestry as one of the alternatives. Intercropping under hardwood species, livestock grazing in managed plantations and windbreaks are few characteristic agroforestry systems in temperate zone. SAQ. 2 What are the major types of agroforestry systems? 20 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system 2.7 Factors which determine the existence of an agroforestry system 1. Environmental and agroecological factors Any agroforestry system composed of living components i.e. crops, trees, pasture and animals. Living things are sensitive to the environmental factors. Different organisms require different environmental conditions for their growth, development and reproduction. Environmental conditions of a particular locality determine the suitability of the organisms that can be thrive in that locality. Therefore the existence of an agroforestry system in a locality primarily determine by the environmental and agroecological factors of the locality. 2. Socio-economic considerations. In addition to above environmental and agroecological factors socio economic factors of an area too determine the existence of particular type and form of an agroforestry system in that area. Human population pressure, availability of production resources like labor, proximity and accessibility to market are few determinants. Though the agroclimatic conditions are similar in two different areas, variation of socio-economic factors in that two area forms two types of agroforestry systems. Shifting cultivation and taungya are widespread agroforestry systems in most ecological regions. But variations between the systems can be observed depending on the variations of existing situations. Therefore it is clear the existence of an agroforestry system in a given locality is determined primarily by the ecological factors and the socio economic factors determine the complexity of the system and the degree of intensity of its management. 3. Functional aspects. Some agroforestry systems perform certain useful functions such as soil conservation. Therefore in specific agroecological situations like sloping land require the service of an agroforestry system having erosion control function. If it is a wind prone area shelterbelts and windbreaks to be established. Summary Ecological factors determine the distribution of agroforestry system all over the world. Study of distribution of agroforestry systems is important in livelihood development of farming communities, global agricultural production and environment. Further the study of the distribution and quantification of the extent under agroforestry is important for the personnel involved in agricultural production, planning and policy development. Agroforestry is an ancient practice adopted by the farmers mainly in tropics as well as temperate zone. Establishment of International Council for Copyright © 2019, The Open University of Sri Lanka 21 AGI5373 Agroforestry Session 2 : Distribution of Agroforestry system Research in Agroforestry (ICRAF) in 1977, the ancient practice of land use pattern was institutionalized and named it as agroforestry. The existing agroforestry systems have been classified into three major types based on their structure. These are Agrosilvicultural system (crops + trees), Silvopastoral system (trees and pasture/animals) and Agrosilvipastoral system (crops + pasture/animals + trees). Existence of an agroforestry system in a particular region decide by the environmental and agroecological factors, socio-economic considerations and functional aspects. Learning outcomes After going through this session the students should be able to;  Identify the different agroforestry systems in the world  Explain the importance of study the distribution of agroforestry systems  Understand the factors determine the existence of an agroforestry system in particular area Answers for SAQs SAQ 1 + To improve the livelihood of farming communities + To assess the global agricultural production + To assess the environmental services or the protective functions of agroforestry + important for the personnel involved in agricultural production, planning and policy development. SAQ 2 + Agrosilvicultural system (crops + trees) + Silvopastoral system (trees and pasture/animals) + Agrosilvipastoral system (crops + pasture/animals + trees). Recommended reference P.K. Ramachandran Nair, An Introduction to agroforestry. 22 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system Session 3 Productivity of Agroforestry system Content Introduction 23 3.1 Productivity 23 3.2 Productivity of agroforestry system 24 3.3 Growing interest on alternative land uses 24 3.4 Effect of trees on soil fertility 25 3.4.1 Biological nitrogen-fixation 26 3.4.1.1 Nitrogen fixing trees (NFT) 27 3.4.1.2 Contribution of tree species to fix atmospheric nitrogen in agroforestry Systems 27 3.4.2 Nutrient cycling 28 3.4.3 Addition of soil organic matter 30 3.5 Effect of trees on soil conservation 30 Summary 31 Learning objectives 31 Introduction Productivity of an agroforestry system can be defined as its efficiencies of producing biomass and provision of certain environmental service /protective functions. Trees are one of the major components of any agroforestry system. Therefore trees contribute more to the productivity of agroforestry systems. The negative impacts of high input agriculture such as fertility degradation of soil, soil erosion and environmental pollution encourage the global community to revisit the existing land use practices in agricultural production such as large scale monoculture. As an alternative land use system agroforestry attracted much attention. Comparatively its ability to produce more biomass than monocrops, potential environmental services such as improvement and maintenance of soil fertility, soil conservation, conservation of water, carbon sequestration and biodiversity conservation has a big potential to solve the problems created by high input fuel driven agricultural practices after green revolution. 3.1 Productivity 23 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system Very simply productivity can be defined as a measure of the efficiency of a person, machine, factory, business, system etc. in converting inputs into useful outputs. This can be determined by dividing average output per period by the total costs incurred or resources such as capital, energy, material, labor consumed in that period (input). In other word productivity measures how efficiently production inputs are being used to produce a given level of output. 3.2 Productivity of agroforestry system Now we will try to relate the term productivity to an agroforestry system. Any system requires some sort of inputs to produce something (output). According to above definition to determine productivity of a system input and output are important. So what are the inputs of an agroforestry system? basically carbon dioxide, water, plant nutrients and energy are the inputs. Then what are the output? Biomass (product of the system) and the service /protective functions provide by the system are the output. Therefore the productivity of an agroforestry system means its efficiency of producing biomass and provision of certain environmental service /protective functions. Trees are the major component of any agroforestry system. Hence trees contribute to the productivity of agroforestry system ( other components i.e. crop and livestock too contribute to the productivity. But here trees are intentionally included to the system to improve the productivity. Therefore much attention has given to trees). However in this session we will concentrate only on environmental services provided by agroforestry systems and their advantages and efficiency over monoculture. 3.3 Growing interest on alternative land uses The green revolution or the dramatic increase in food production especially the cereal grain yield started spreading all over the world in 1950 – 1960. The high yielding verities introduced are very efficient in converting water, plant nutrients (fertilizer) and other inputs to yield. This led to increased application of chemical fertilizer to maintain soil fertility. Establishment of large scale irrigation schemes to fulfil the water requirement for farming gradually removed the natural forest cover. Required to apply more pesticides, fungicides and weedicides to get the potential yield. The amount of burning fossil fuel for farming activities has increased. Large scale monocultures are prominent in this system. All these activities created lots of environmental problems like soil, water and air pollution, depletion of soil fertility, soil erosion, declining biodiversity etc. At the end of the 1990s, international community revisited through the achievements of global food production as well as the negative impacts resulted. The concern about environmental issues led to think about alternative land uses. As a result agroforestry was recognized as one of the 24 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system alternatives to solve this problem due to its multifunctional agriculture and important environmental services over monoculture. The main environmental service functions of an agroforestry system are; 1. Improvement and maintenance of soil fertility through nitrogen fixation, nutrient cycling and adding organic matter to the soil). 2. Soil conservation. 3. Conservation of water (quantity and quality). 4. Carbon sequestration. 5. Biodiversity conservation. Efficiency of all the functions above are determined mainly by the trees in the system. In other word trees contribute to the productivity of an agroforestry system through performing above environmental functions. However in this session we are going to limit our discussion only to improvement and maintenance of soil fertility and soil conservation. All other services will be discussed in the later part of this course. SAQ. 1 Why global community wanted to revisit the high input agriculture emerged after green revolution? 3.4 Effect of trees on soil fertility Soil fertility is the quality of a soil that enables it to provide compounds in adequate amounts and proper balance to promote growth of plants when other factors, such as light, moisture, temperature, and soil structure are favorable. Soil fertility is one of the key factors which determine sustainable crop production and food security. Fertility is determined by physical, chemical and biological properties of the soil. It has been proven that agroforestry systems have a great potential in improving and maintaining soil fertility through improving physical, chemical and biological properties of the soil. This has been proven by our rural farmers with their own experience in chena cultivation. The farmers got high yield by planting crops in undisturbed forest soil (planting crops after clearing forests). Further the research has proven that all physical, chemical and biological properties which determine the soil fertility are in optimum levels in forest soil over other agricultural systems. Forest soils are rich in organic matter. Also the water holding capacity is high. But we can’t say the attributes of soil in an agroforestry system is almost similar to the attributes 25 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system of a soil in a natural forest. When compare with the soils of other agricultural systems especially the monocultures, fertility of the soil in agroforestry systems are higher. However in this session we will limit to our discussion only into the trees involvement in nitrogen fixation, nutrient recycling and provision of organic matter in an agroforestry system since these are the very important functions of trees in an agroforestry system with respect to the improvement and maintaining soil fertility. 3.4.1 Biological nitrogen-fixation Can you remember what nitrogen-fixation is? Nitrogen fixation is the process by which atmospheric nitrogen (N2), is converted either by a natural or an industrial means to a form of nitrogen such as ammonia. In nature, most nitrogen is harvested from the atmosphere by microorganisms to form more reactive nitrogen compounds such as ammonia, nitrites, and nitrates that can be utilized by plants ( which is named as biological nitrogen fixation – BNF). Nitrogen is the most important element in crop production since it plays a vital role in plant growth and development through protein synthesis. Nitrogen is a major constituent of amino acids, the building blocks of protein. Nitrogen is also one of the chemical components of DNA. Therefore the nitrogen requirement is very high in agricultural production. Full filling this requirement by adding chemical fertilizer having nitrogen is costly as well as it creates environmental problems. But through biological nitrogen fixation, the nitrogen fixing tree species can convert atmospheric nitrogen into different nitrogen compounds the plants can be absorbed. This is very cheap and environment friendly way of make available nitrogen for crop growth. Therefore the presence of nitrogen fixing trees in an agroforestry system has an immense value in improving soil fertility. Planting herbaceous legumes such as ground nut, mung bean, cowpea, wing bean, soya bean etc. is a common practice in agricultural systems to enrich soil with nitrogen. According to Nutman ,1976; LaRueandPatterson, 1981;Gibsonetal.,1982;IRRI, 1988; Peoplesand Herridge, 1990 the nitrogen fixation rates for most herbaceous legumes are in the range of 40 to 200kg N/ha/year. Though more emphasis given to the nitrogen fixing herbaceous plants, there are tree species having nitrogen fixing qualities. Attention given for the nitrogen fixing trees increased with the growing interest on agroforestry. 26 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system 3.4.1.1 Nitrogen fixing trees (NFT) According to Brewbaker,1987a;BrewbakerandGlover,1988 about 650 tree species have been identified as nitrogen fixing as well as another several thousand of trees suspected to be nitrogen fixing. There are two ways of fixing atmospheric nitrogen by plants i.e. symbiotic and non – symbiotic nitrogen fixation. Here the symbiotic nitrogen fixation is more important in agricultural production since the rate of fixation is higher than the non-symbiotic fixation. (This nitrogen demand is very high in crop production). The non-symbiotic fixation depends on some other factors like soil organic matter. Therefore less important in agriculture. In symbiotic fixation legumes forms an association with the bacteria cold Rhizobium. The bacteria invade the root hairs of host plant where they multiply and stimulate the formation of a structure called root nodules. The bacteria living in the root nodule convert free nitrogen to ammonia, which the host plant utilizes for its development. To ensure sufficient nodule formation and optimum growth of legumes, seeds are usually inoculated with commercial cultures of appropriate Rhizobium species before planting. Gliricidia sepium, Leucaena leucocephala, Sesbania grandiflora, Acacia spp. Albizia spp. Erythrina spp. and Calliandra calothyrsus are few common nitrogen fixing woody perennials which can be included in agroforestry systems. Alnus, Casuarina, and Allocasuarina are few non leguminous trees but fixing nitrogen with the association of microorganism called as Frankia an actinomycetes can include in agroforestry systems. Pulses and groundnut are few non woody crops which can fix nitrogen and included in Agrosilvicultural systems. Stylosanthes species and Centrosema pubescens are vines that fix nitrogen. Calopogonium caeruleum, Calopogonium muconoides, Pueraria javanica, Pueraria phaseoloides few other nitrogen – fixing vines can include in plantations. 3.4.1.2 Contribution of tree species to fix atmospheric nitrogen in agroforestry systems Growing of nitrogen-fixing trees or deep-rooted trees and shrubs in agroforestry systems increase nitrogen availability in such soil through biological fixation of nitrogen. According to Anderson and Sinclair, 1993; Harmand and Njiti, 1998; Ganry et al., 2001, planted tree fallows are a 27 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system potential solution to declining soil fertility due to shortened fallow periods in areas where slash-and-burn is still practiced. In 2001, Harmand and Balle proven that nitrogen availability, determined by inorganic soil nitrogen or aerobic nitrogen mineralization at 0 to 20 cm depth, and crop yields can be significantly higher after a rotation of nitrogen-fixing trees than after other tree species or grass fallows. Szott and Palm (1996), showed that leguminous tree fallows greatly increased the total of phosphorus, potassium, calcium and magnesium stocks in the biomass, litter and exchangeable cations/ available phosphorus (soil; 0-45cm) over leguminous herbaceous fallows. They further suggested that fast-growing leguminous trees can accelerate restoration of nitrogen, phosphorus and potassium stocks in the crop layer but may not completely restore calcium and magnesium stocks. Few nitrogen fixing tree species commonly used in agroforestry systems and their nitrogen fixation rates are given below; Gliricidia sepium (13kg/ha/yr.), Leucaena leucocephala (100 – 500kg/ha/yr.), Acacia mearnsii (200kg/ha/yr.), Casuarina equiselifolia (60 – 110kg/ha/yr.), Erythrina poeppigiana (60kg/ha/yr.) and Faidherbia(Acacia)albida (20kg/ha/yr.). SAQ. 2 What is meant by biological nitrogen fixation 3.4.2 Nutrient cycling Living cells are made up of primarily by six major elements, hydrogen, oxygen, carbon, nitrogen, phosphorus, and sulfur. Organisms capture these elements from the environment for the metabolism and again release them to the environment after death. What it means is, in an ecosystem the plant nutrients are in a state of continuous, dynamic transfer. The way that soil nutrients move through the earth system, including within food production systems, is called nutrient cycling (According to Brady & Weil 2002, nnutrient cycling is the flux of nutrients within and between the various biotic or abiotic pools in which nutrients occur in the soil environment). Nutrient cycling is an essential process for the existence of organisms in any ecosystem. But this is a complex process. Weathering of rocks and minerals which provide nutrient to the system, its moves through different components of ecosystem, transformations that take place in different spheres i.e. biosphere, atmosphere, lithosphere, and hydrosphere. This involves living organisms as well as non-living components in the ecosystem. They also involve biological, geological, and chemical processes. Each and every nutrient has a separate cycling pathway (e.g. carbon cycle, oxygen cycle, phosphorus cycle, nitrogen cycle etc.), collectively known as biogeochemical cycles. 28 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system However at this point we are not going to discuss all above. What we need to study, simply the nutrient transferring from soil to plants and back from plant to soil ( which can be defined as nutrient cycling). The plants capture nutrients from the soil for their metabolic processes. During metabolism these nutrients are combining in various ways and concentrating in the cells. Some nutrients are stored (e.g. carbon), some are used to produce various tissues (e.g. nitrogen). For example hydrogen, oxygen, carbon and nitrogen make up about 99% of the mass of most cells. During growth and development some plant parts are returned to the soil (e.g. leaves) called as litterfall, some time we purposely incorporate plant parts to soil as manure or mulching purposes, ultimately after harvest remaining plant parts are added to the soil. All these added biomasses decomposed by the soil microorganisms and the nutrients in the biomass released to the soil which can be recaptured by plans. So it is clear the recycling process is essential to make available plant nutrients in soil. In other word maintain soil fertility or the capacity of the soil to provide essential nutrients for plant growth. Let us now see few important points on nnutrient cycling in agroforestry systems: Nutrient cycling can be seen in all soil plant systems. But varying degrees. However research revealed that the nutrient cycling is very efficient in tree based soil plant systems including agroforestry because of the presence of trees over plants, crops etc. Presence of woody perennials are able to recycle nutrients year after year due to their long lifespan some time 10 – 15years. One of the characteristic features in ecosystems having trees is accumulation of large amount of biomass and thus accumulation of more nutrients. The deep root system of trees can absorb nutrient from deep soil layers and pumped it to top soil through nutrient cycling. Decaying roots (where 20 – 30% of the total biomass of a tree is accumulated) add more organic matter to the soil. Large amount of litterfall of trees is an another factor, has a positive impact on nutrient cycling. Removal of nutrient from soil plant system as harvest is less in tree species like fruits over agricultural crops. Also trees reduce the nutrient losses by preventing leaching and erosion. Further the control of erosion and stabilization of soil by the tree roots help to maintain the physical properties of the soil. Nutrient cycle of any soil plant system consists of nutrient inputs, outputs and nutrient balance. Nutrient inputs are addition of nutrients to the system from outside such as application of chemical fertilizers, biological nitrogen fixation, manure/organic matter produced outside and incorporated to the system, rain, rock weathering etc. The outputs are those that leave from the 29 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system system as harvest, through leaching, erosion, volatilization, denitrification etc. Nutrient balance is the difference between nutrient inputs and outputs or the nutrient turnover of the system. Turnover is important for the fertility of soil. If we compare a natural forest, agricultural system and an agroforestry system the turnover is very high in a natural forest due to less amount of output and it act as a kind of closed system. In the agricultural system the turnover is very low since both the input and output are very high. An agroforestry system lies in between these two. Therefore the nutrients in an agroforestry system can be reused again and again for the production. However all factors pointed out above vary between different agroforestry systems due to varying tree densities, management practices, climatic factors etc. However it is easy to improve the efficiency of nutrient cycling of an agroforestry system by manipulating its components, management practices etc. For examples by using deep rooted trees can capture nutrients in deep soil layers, by using legumes can fix more nitrogen. 3.4.3 Addition of soil organic matter Soil organic matter plays a vital role in improvement and maintenance of all physical, chemical and biological properties of soil. The sources of organic matter in the soil are plant material and dead soil fauna including microbes. However majority is from plant material. There are two types of organic matter in the soil namely, humus and litter. Humus are the fully decomposed organic matter (end product of organic matter decomposition) which improves the cation exchange capacity, water holding capacity and structure of the soil. Litter is the partially decomposed organic matter. Agroforestry systems are important in accumulation and maintenance of soil organic matter. Both trees and crops build up the organic matter content in soil. But varying amount and quality. It is obvious that the biomass of trees is greater than crops and thus add more organic matter to the soil than crops. Decomposition rate of lignified woody material is slow. Hence form poor quality litter (litter quality means the nutrient content and relative rate of decomposition of plant material). Plant residues having high nitrogen contents decompose easily and form quality organic matter. Therefore the inclusion of nitrogen fixing trees (tree legumes) into the agroforestry systems add quality litter to the soil. Addition of organic matter to the soil by woody perennials is continuous and steady where as in crops it is seasonal. During the periods of harvesting they add more organic matter to the soil. Biomass of tree roots too provide considerable amount of organic matter to the soil when compared to the root biomass of crops (fine root biomass). Sloughing- off of roots of standing trees (continuous degeneration of roots) is a major source of organic matter in soil. 30 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system SAQ. 3 What is meant by nutrient turnover of a soil plant system? All these factors discussed in above 3.4.1, 3.4.2 and 3.4.3 are important in improving the productivity of soil which is an outcome of the productivity of an agroforestry system. Now we will move to see another productivity function of an agroforestry system i.e. soil conservation 3.5 Effect of trees on soil conservation Soil conservation includes both erosion control and maintenance or improving productivity of soil. Erosion of soil cause low fertility in soil due to loss of organic matter and plant nutrients and thus reduced crop productivity. Therefore the soil conservation is an important factor in sustainable food production. Mainly trees contribute to productivity in agroforestry through reducing erosion. All most all trees, shrubs and crops have a positive impact on soil conservation. However trees play the major role. Proper arrangement of trees, shrubs and crops in the field protect the direct exposure of soil surface to the rain fall and thus reduced splash erosion. Therefore the agroforestry systems can reduce rainfall erosivity (erosivity is the term used to describe the potential of raindrop impact on erosion). However this can be varying with the system. Addition of organic matter into the soil improve the structure and stability of soil and lower the detachability of soil particles. Further improves infiltration and thus reduced runoff. All these factors reduce the erodibility of soil (nonresistance of soil for the erosion). Trees as well as strip grasses and hedges in allay cropping act as barriers to the runoff and increase infiltration. Natural litter fall or pruning residues cover the soil and reduce the impact of raindrops. Wind breaks and shelter belts are useful in preventing wind erosion. Activity 1 What are the adverse effect of trees in an agroforestry system? Summary Trees contribute more on the productivity of agroforestry systems. As an alternative land management system agroforestry has a big potential to solve 31 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 3 : Productivity of Agroforestry system problems of high input agriculture through its ability to produce more biomass than monocrops, potential environmental services such as improvement and maintenance of soil fertility, soil conservation, conservation of water, carbon sequestration and biodiversity conservation. Learning objectives After following this session the students should be able to; Understand what productivity of an agroforestry system is? Understand the requirement of alternative land use practices in food production Understand the environmental services of agroforestry systems ( in this session it has limited to the maintenance of and improvement of soil fertility and soil conservation. Answers for SAQs SAQ. 1 – Due to its negative impacts such as degradation of soil fertility, soil erosion, depletion of biodiversity etc. Further the costly inputs such as seeds of improved varieties, agrochemicals, requirement of mechanization and ever growing fuel cost. SAQ. 2 – Process by which atmospheric nitrogen is converted into more reactive nitrogen compounds such as ammonia, nitrites and nitrates by certain microbial associate with plant roots SAQ. 3 – There are nutrient inputs as well as outputs in soil plant systems. The different between input and the output is nutrient turnover. Recommended reference https://link.springer.com/chapter/10.1007/978-94-007-7723-1_7 http://www.fao.org/3/xii/ms20-e.htm http://www.fao.org/3/w0312e/w0312e06.htm 32 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session Session 4 Role of trees in Agroforestry Session Content Introduction 33 4.1 Productivity of plants/trees 34 4.2 Principles behind plant productivity 34 4.2.1 Leaf area of plants 35 4.2.2 C3, C4 and CAM plants 35 4.3 Primary productivity of plants 37 4.4 Selection of tree species for agroforestry 37 4.5 Multipurpose trees (MPTs) 39 4.6 Environmental services of trees in agroforestry 39 Summary 41 Learning outcomes 41 Introduction We are deliberately integrating trees with crops/livestock/pasture in agroforestry. Therefore trees play more prominent role in any agroforestry system. Major roles of trees in an agroforestry system are production and provision of services. Products include food (fruits, nuts, leaves), fiber, oils, beverages, gums, resins, latex, flavors, fodder for livestock, medicines, timber, firewood. In other word biomass. Services are soil conservation, modifying micro-climate, nitrogen fixation, increase of soil carbon, addition of soil organic matter, provision of shelter from wind and sun, conservation of biodiversity, regulation of water, ground water recharge, provision of habitat for other animals and insects. Sugar produce in green plants/trees through the process of photosynthesis is the production of a tree. Leaf area of plants, pathways of fixing carbon and environmental factors are few factors which determine production. However part of the sugar produced by the plant burnt through the process of respiration to produce energy required for growth, development and reproduction of the plant. The total amount of sugar fixed by plant is referred to as gross primary productivity (GPP) since all energy fixed by a plant can be converted into sugar. The difference between GPP and the sugar burnt at respiration is the net primary productivity (NPP). NPP is the portion of biomass available for the consumption of all other animals including human being, called as production. Copyright © 2019, The Open University of Sri Lanka 33 AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session There are important factors to be considered when selecting trees for an agroforestry system since the trees have to provide services too. Selection of multipurpose trees (MPTs) are important in this regard. 4.1 Productivity of plants/trees As you aware now any agroforestry system is dominated by plants i.e. trees, crop and pasture. Within the system trees (woody perennials) play a major role in productivity and sustainability. In other word trees provide us two major things i.e. products and services. The products are food (fruits, nuts, leaves), fiber, oils, beverages, gums, resins, latex, flavors, fodder for livestock, medicines, timber, firewood. In other word biomass. Services are soil conservation, modifying micro-climate, nitrogen fixation, increase of soil carbon, addition of soil organic matter, provision of shelter from wind and sun, conservation of biodiversity, regulation of water, ground water recharge, provision of habitat for other animals and insects. However in this session we will concentrate only to the product/productivity of plants/trees. Most important factor that the total productivity of the system depend, is the productivity of individual plants. Productivity of different plant species are different. Therefore to optimize the total productivity of the system, selection of plant species to include in the system should be done in a scientific basis. Selection of trees (what trees to be included?), number of trees to be included from a particular species (how many trees?) and their temporal and special arrangement in the system (how are they best arranged?) are important. For this we should have some knowledge on productivity of plants and the principles govern the plant productivity. 4.2 Principles behind plant productivity First, we will see what plant production is? Have you heard the term “photosynthesis”? Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy that can be transported and stored. During photosynthesis in green plants, light energy is captured and used to convert water and carbon dioxide into oxygen and energy rich organic compounds (biomass). In other word green plants and trees use photosynthesis to make food from sunlight, carbon dioxide and water (figure 4.1). The biomass or the food is the plant production. Figure 4.1 Photosynthesis reaction 34 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session Therefor the understanding of principles govern by the photosynthesis is very important to manage agroforestry systems and exploiting the production potential. Management of plant in such a way improves the exploitation of photosynthesis and thus increased production. Photosynthesis or the fixation of carbon by the green plant is a complex process which involves series of biochemical reactions. This is not a session to explain all those things. However a few important points are highlighted here. 4.2.1 Leaf area of plants The place where the photosynthesis that take place is chloroplast. These structures are concentrated in upper part of green leaves. Therefore the green leaves surfaces are considered as the primary photosynthetic organs. The radiant energy that required for the photosynthesis comes from visible spectrum of sun’s rays ( 400nm to 700nm wavelength). This amount is 40% - 50% of the sun light received by the earth, and this is the amount used by the plants for photosynthesis. We called it as photosynthetically active radiation (PAR). So what we can conclude at this point is increased leaf area capture more PAR and thus more plant production. 4.2.2 C3, C4 and CAM plants There are three pathways of fixing carbon in green plants. C3 pathway - produces 3-phosphoglyceric acid (PGA) or 3- carbon acid as the first product of the photosynthesis process. The plants fixing carbon through C3 pathway are called as C3 plants. Examples for such plants are Sunflower, Spinach, Beans, Rice, Cotton. wheat, oats, barley, rye, legumes, tobacco, potatoes and almost all tree species. C4 pathway - produces oxaloacetic acid (OAA) or 4 -carbon compound as their first product of the photosynthesis process. The plants fixing carbon through C4 pathway are called as C4 plants. Sugarcane, Sorghum and Maize. CAM pathway – in this pathway the plants absorb the energy of the sunlight at the daytime and use this energy for fixing the carbon dioxide at nighttime. We called this pathway as crassulacean acid metabolism or CAM. However at the presence of optimum moisture conditions some of the CAM plants follow C3 pathway. The plants having CAM process are known as CAM plants. Cacti, orchids. Pineapple and Agave spp. ( No need of going deep on this pathway for this course agroforestry. But you are interested you can refer basic textbooks on plant physiology) What we have to take our mind at this point is the variation of carbon assimilation (production) of this three groups of plants. No photorespiration (respiration during daytime) in C4 plants when compared to C3 plants. As you are aware plant respiration is the process of plants using up the sugars made through photosynthesis and burning them by using Copyright © 2019, The Open University of Sri Lanka 35 AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session oxygen to produce required for growth, development, reproduction and other life processes. This is the reverse of the photosynthesis reaction (figure 4.2). Therefore C4 plant can save lots of carbon during daytime and spend them for biomass production. Also in C4 plants the carbon uptake is increasing with increased light levels. Further the C4 plant can fix carbon better in dimmer light conditions. Therefore the photosynthetic efficiency is high in C4 plants and thus high production rates. Figure 4.2 Reactions of photosynthesis and respiration Environmental factors too have an effect on the carbon assimilation of above plants. See following examples:  C3 plants grow well at an optimum ambient temperature between 65 to 75°F and the soil temperature range from 40- 45°F. They show less carbon assimilation efficiency at high temperature (Therefore these plants are known as cool season or temperate plants). Also C3 plants provide a higher amount of protein than the C4 plants.  C4 plants are annuals or perennials. grow well in temperature range of 90-95°F( therefore known as warm- season or tropical plants). They are much more efficient in utilizing soil nitrogen and gathering carbon dioxide from atmosphere. However the protein content is low as compared to C3 plants.  CAM plants absorbs energy from the sunlight during the daytime and uses this energy at the nighttime for the assimilation of carbon dioxide. This is a kind of adaptation to the periodic drought. Photosynthesis required gas exchange (absorption of carbon dioxide from atmosphere and release of oxygen to atmosphere). This required keep stomata open which accelerate loss of water from plant. Hence this adaptation permits the gas exchange at nighttime when the air temperature is cooler which minimize transpiration. This adaptation can be found in plants grow in arid zone. Example cactus and euphorbias. In orchids and bromeliads (e.g. Pineapple) adapted this pathway to tolerate for low soil moisture. 36 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session 4.3 Primary productivity of plants Knowledge on primary productivity of plants is useful to understand the production of an agroforestry system and to adopt suitable management practices to optimize the production of system. Primary productivity of a plant community is the amount of biomass produced through photosynthesis per unit area and time by plants (by the primary producers) which can be expressed as units of energy (e.g. joules m -2 day -1) or in units of dry organic ma tatter (e.g., kg m -2 year -1). The total energy fixed by plant community is referred to as gross primary productivity (GPP) since all energy fixed by a plant can be converted into sugar. Part of the energy of gross primary productivity is used to produce energy by respiration. Remaining portion is known as net primary productivity (NPP). NPP is the portion of biomass available for the consumption of all other animals including human being. Therefore it is important to manage agroforestry systems by keeping our mind, the increase of net primary productivity SAQ. 1 Why leaf area is important in primary production of a plant? SAQ. 2 Why GPP and NPP are important in agroforestry? 4.4 Selection of trees for agroforestry Trees are the major component in all agroforestry systems. Trees are deliberately integrated with other crops, pasture or livestock. Therefore it is important to select most suitable trees for the system since it is not easy to replace them once they have been planted. Following factors should be kept in our mind when selecting tree species for the system. 1. Production factors Here we have to consider the photosynthetic pathways discussed earlier. Selection of trees with high NPP is useful for higher production. 2. Needs of farmers Selected species should meet the needs of the farmer. This depend on the expected products of the farmer i.e. food, fodder, fuel wood, timber etc. Involvement of entire farm family is important when selecting trees. Not only the products, conservation needs too have to be address. 3. Environmental adaptations Selected trees should have the ability to adapt to the climate, soil and other conditions of the locality. This is more important in introducing exotic species. 4. Ease of maintenance Selected species should be easily maintained. To maintain some trees require more knowledge and skills. Farmers has to decide the species after a proper assessment of the available resources, training etc. Copyright © 2019, The Open University of Sri Lanka 37 AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session 5. Availability of planting material Planting material should be easily obtained. Reasonable price of the planting material is important. Farmers too should have the knowledge, skills and ability to propagate especially if required vegetative propagation. 6. Competition Selected trees should not compete especially with crop for the resources like moisture, nutrient, sunlight etc. or the competition should be minimal. Selection of trees with less water requirement, deep tap root systems which can draw water from deep soil minimize the competition for water. Selection of trees utilized less amount of nutrient and selection of Leguminous tree species which fix atmospheric nitrogen minimize the competition for plant nutrient. The canopies of selected trees should not interrupt sunlight falling on the crops. Light branching habit permit the penetration of light into the ground. By pruning can improve the light penetration. But the selected trees should have the ability to withstand pruning. 7. survival rate and easy establishment Trees with high survival rates prevents the gap formation in the field after planting. Trees having faster root regeneration, hardy trees which can tolerate transplanting shocks are easy to establish. 8. fast growing habit and easy management Should be essentially fast growing. This will ensure short rotation i.e. the period between planting and final harvesting. 9. High palatability as fodder If livestock included to the system, they require fodder. Therefore the tree species selected are palatable to livestock and had a high digestibility. 10. Soil stabilization attributes This will help to prevent erosion. 11. Withstand to management practices Extensive pruning and lopping of the trees are required to maximize production. Therefore the selected trees should have the ability to withstand such treatment without restricting growth rate. 12. Nutrient cycling and nitrogen fixation attributes Trees can play an important role in recycling nutrients, leached down through the soil profile and minerals released from weathering parent material such as rocks and sediments. The other important factor is the ability to fix atmospheric nitrogen into organic nitrogen. leguminous trees are important in this regard. 38 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session 4.5 Multipurpose trees (MPTs) Agroforestry is the intentional integration of trees with agricultural crops and livestock/pasture. Therefore the success of any agroforestry system highly depends on the production potential of the trees. In section 1.4 above we highlighted some important factors to be considered when selecting any tree species for an agroforestry system. In this section we will try to formulate an answer for the common question in agroforestry i.e. which species are going to select for particular system? Very simple answer for this question is “agroforestry species”. Let us now see what “agroforestry species” are? These are the woody or herbaceous species which are suit to integrated combination cultures like inter cropping (there are under exploited lesser known both woody and herbaceous species which fulfil this criterion). These are also known as “multipurpose trees” (MPTs) or “multipurpose trees and shrubs” (MPTS). If we elaborate the term further, MPTs are the trees and shrubs which are deliberately kept and managed for more than one preferred use, product, and/or service. Fruit, fodder and fuelwood trees are few examples for MPTs. 4.6 Environmental services of trees in agroforestry Trees have to play two major roles in any agroforestry system. Those are production and provision of services. We have learnt the basis of production in previous sections 1.1, 1.2 and 1.3. Here we will concentrate on services provided by the trees in an agroforestry system. 1.Prevention of soil erosion and stabilization of soil The tree canopies act as barriers and reduces the velocity of rainwater droplets before strike the soil surface. This prevent raindrop splash. In other word the breakdown of soil aggregates and dispersal, which is the first step of soil erosion. Trees slow down the runoff rainwater which also prevent soil erosion. Planting trees as hedgerows along the contours help to prevent soil erosion and stabilize the soil. Tap root systems of trees also stabilize the soil. 2. Water quality improvement The minimal runoff traps the sediment which prevent accumulation of sediment in water bodies and thus water quality improvement. 3. Act as windbreaks Windbreaks are strips of trees, shrubs, and vines planted very closely along the edges of croplands perpendicular to the direction of winds. Windbreaks minimize the negative effects of wind on crops and soils (wind erosion). Further It reduces the evapotranspiration of the cropland. 4. Improve the fallow period. Time gap between two rotation cycles is known as fallow period. To improve the soil fertility we can plant fast growing trees during the fallow period. Copyright © 2019, The Open University of Sri Lanka 39 AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session Inclusion of species that fix nitrogen during fallow period will recover the soil faster. 5. Nutrient recycling The deep tap root systems of the trees can absorb nutrient in deep strata of the soil. 6. carbon sequestration Trees are capable of capturing atmospheric carbon dioxide to produce biomass. This will help to maintain the carbon dioxide level in atmosphere under favorable level. 7. Conservation of biodiversity The different tree species in the system itself improve the biodiversity. Also trees provide habitat for lots of other living animals and organisms. 8. Recycling water The trees with deep tap root systems can absorb water in the deep strata of the soil and release to the atmosphere through transpiration. This will help for the function of water cycle. 9. Help for the ground water recharge Minimal runoff due to trees improve the infiltration, deep percolation and thus ground water recharge. 10. Improve soil organic matter and thus soil carbon Degraded biomass provides soil organic matter to the soil. 11. Nitrogen fixation The plants belong to family Leguminosae can fix atmospheric nitrogen for the use of plant. SAQ. 3 What are the two major functions of trees in any agroforestry system SAQ. 4 What is the importance of MPTs in agroforestry Activity 1 Gather information on MPTs found in agroforestry systems in Sri Lanka 40 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session Summary Trees play more prominent role in any agroforestry system. Major roles of trees in an agroforestry system are production and provision of services. Sugar produce in green plants/trees through the process of photosynthesis is the production of a tree. However part of the sugar produced by the plant burnt through the process of respiration to produce energy. required for growth, development and reproduction of the plant. The total amount of sugar fixed by plant is referred to as gross primary productivity (GPP). The difference between GPP and the sugar burnt at respiration is the net primary productivity (NPP). NPP is the portion of biomass available for the consumption of all other animals including human being, called as production. There are important factors to be considered when selecting trees for an agroforestry system since the trees have to provide services too. Selection of multipurpose trees (MPTs) are important in this regard. Learning outcomes After going through this session the students should be able to;  Identify the two major roles of trees in an agroforestry system i.e. production and services.  Understand the NPP as the production of an agroforestry system.  Identify the factors to be considered when selecting trees for an agroforestry system.  Understand the services of an agroforestry system. Answers for the SAQs. SAQ. 1 The place where the photosynthesis (primary production) that take place is chloroplast. Chloroplasts are concentrated in upper part of green leaves. Hence the green leaves surfaces are considered as the primary photosynthetic organs. Therefore the leaf area is important in primary production. For an example increased leaf area fix more energy. SAQ. 2 GPP is the total energy fixed by a plant community. Part of the energy of GPP is used to produce energy by respiration. Remaining portion is NPP. This is the portion of biomass available for the consumption of all other animals including human being. Production of an agroforestry system is therefore NPP. SAQ. 3 Production and provision of services. Copyright © 2019, The Open University of Sri Lanka 41 AGI5373 Agroforestry Session 4 : Role of trees in Agroforestry Session SAQ. 4 MPTs are the trees and shrubs which are deliberately kept and managed for more than one preferred use. Therefore we can get products as well as service from MPTs. Recommended reference P.K. Ramachandran Nair, An Introduction to agroforestry. Section 111 42 Copyright © 2019, The Open University of Sri Lanka AGI5373 Agroforestry Session 5 : Interactions within an Agroforestry System Session 5 Interactions within an Agroforestry System Content Introduction 43 5.1 Types of interactions 43 5.2 Tree crop interactions – (positive effects) 45 5.2.1 Plant microclimate amelioration 45 5.2.2 Nutrient balance 46 5.3 Tree crop interactions – (negative effects) 47 5.4 Tree animal interactions – (positive effects) 47 5.5 Tree animal interactions – (negative effects) 4.8 5.6 Importance of study on interactions 4.8 Summary 49 Learning outcome 50 Introduction An agroforestry system composed of different components such as tree, crop, animal, pasture etc. There are positive (beneficial), negative (harmful) and neutral interactions between these components called as component interactions. The balance between negative and positive interactions is known as net interaction. The positive interactions have complimentary effect on the system and they always increase the production and the negative interactions are competitive and reduces the production of the system. Therefore the net interactions of the system determine the production. Amelioration of microclimate and maintaining and improvement of nutrient balance are positive or complimentary effects while competition for water, nutrient and light are negative or competitive effects. The major component of an agroforestry system is trees. Therefore there are tree – crop and tree - animal interactions in an agroforestry system. Unders

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