ALTERNATIVE AND IMPROVED LAND USE SYSTEMS TO REPLACE RESOURCE-DEPLETING SHIFTING CULTIVATION

P. K. R. Nair
International Council for Research in Agroforestry
ICRAF
Nairobi, Kenya

INTRODUCTION

Shifting cultivation has been, and still continues to be, the mainstay of traditional farming systems over vast areas of the tropics. It is estimated to be extending over approximately 30 percent of the exploitable soils of the world in 360 million ha, and supporting over 250 million people or about 8 percent of the world's population (FAO/SIDA, 1974). However, over the years, several factors have caused progressively increasing strains and stresses on the shifting cultivators and on the efficiency of the practice, so that in certain cases the practice has become highly resource-depleting and severely environment degrading. But the very fact the practice has stood the test of time over centuries indicates that it involves certain beneficial elements which could effectively be exploited. Since the practice is so widespread and important to the livelihood of so many people, it is impossible to dispense with it completely in one stroke. Therefore, while it is imperative to look for improvements and alternatives to shifting cultivation, it is also important to ensure that the beneficial aspects of the traditional practice are retained /incorporated in the improved or "new" systems.

THE SCENARIO OF SHIFTING CULTIVATION

The practice of shifting cultivation can be described, in simple terms, as a land use system in which forested land is cleared and cropped for a few years, and then left for the regeneration of the bush (fallow period), the duration of the fallow period being much longer than that of the cropping period. Although there are several variations in the practice in different parts of the world, in general, all forms of shifting cultivation follow five stages: site selection, cleaning, burning, cropping and fallowing (Watters, 1960).

The literature on various aspects of shifting cultivation is voluminous and fairly well documented. Grigg (1974) has examined the evolution of shifting cultivation as an agricultural system, -while the anthropological and geographical information on the practice have been compiled by Conklin (1963). Sanchez (1973) , Greenland (1974) and Ruthenberg (1980) have described the various forms of shifting cultivation and studies on soils under shifting cultivation have been evaluated in excellent publications on the subject by Nye and Greenland (1960), Newton (1960), FAO/SIDA (1974) and Sanchez (1976).

Perhaps the most striking beneficial aspect of shifting cultivation that deserves to be exploited and incorporated in alternative and improved land use systems is the restoration of soil productivity that takes place during the fallow period through the biological processes associated with revegetating the area. Before clearing the forest a closed nutrient cycle exists in the soil-forest system. In this, most nutrients are stored in the biomass and topsoil and a constant cycle of transfer of nutrients from one compartment of the system to another operates through physical and biological processes of rainwash, litterfall, root decomposition and plant uptake. The amount of nutrients lost from such a system are negligible. Clearing and burning the vegetation leads to a disruption of this closed nutrient cycle. During burning the soil temperature increases, and afterwards more solar radiation is received on the bare soil surface resulting in higher soil and air temperatures (Ahn, 1974; Lal et al., 1975). This change in the temperature regime causes resultant changes in the biological activity in the soil. The addition of ash to the soil by burning causes important changes in soil chemical properties and organic matter content (Jha et al., 1979). In general, exchangeable bases and available phosphorus increase slightly after burning; pH values also increase, but usually only temporary. Organic matter content is also expected to increase by burning, mainly because of the unburned vegetation left behind (see Sanchez and Salinas (1981) for a detailed discussion on soil dynamics after clearing tropical forests).

These changes in the soil after clearing and burning result in a sharp increase of available nutrients, so that the first crop that is planted is considerably benefit. Afterwards, soil becomes less productive and crop yields decline. The main reasons for the decline of yield are soil fertility depletion, increased weed infestation, deterioration of soil physical properties, and increased insect and disease attacks (Sanchez, 1976). Finally, the farmers feel that further cultivation of the fields will be difficult and non-remunerative, they abandon the site and move on to others, knowing well that they can return to the site after the lapse of a few years, because the site so abandoned will be reinhabited by natural vegetation (forest fallow) and during the fallow period, the soil will regain its fertility and productivity. (This phenomenon of improvement of soil fertility during the fallow period has been demonstrated by numerous studies, for example, Nye and Greenland, 1960; Sanchez, 1976; Aweto, 1981; Koopmans and Andriesse, 1982; Mishra and Ramakrishnan, 1983).

Thus, the cycle has been repeated in many regions and shifting cultivation has continued for centuries though at low productivity levels. However, over long periods of time when human population pressures have started to increase, the length of the fallow periods has diminished and farmers have returned to the fallow sites before these have had enough time for fertility to be sufficiently restored. The introduction of industrial crops and modern methods of crop production have also caused a shift in emphasis on the importance of fallow period in traditional shifting cultivation.

ALTERNATIVES TO SHIFTING CULTIVATION

It is in this scenario that we have to tackle the question of alternatives/ improvements to shifting cultivation. From the academic point of view, there can be several alternatives; for example, the large-scale establishment of permanent tree crops such as rubber and oil palm, commercial plantations of timber species, sown grassland and extensive ranching, and so on. But these are not viable and practical alternatives to shifting cultivation as land use systems because these practices seldom satisfy the immediate objective of food production (which is the primary motivation for shifting cultivation), and are not compatible with the socio-economic conditions of the shifting cultivators. Successful alternatives/improvements to shifting cultivation should:

i) allow production of food and wood products simultaneously from the same piece of land in a sustainable manner; and

ii) be compatible with the socio-cultural aspirations and economic conditions of the people in order for such practices to be adaptable. The agroforestry approach to landuse becomes quite relevant in this context.

The concepts and principles of agroforestry have been elucidated and its constraints and potentials evaluated from different points of view in several recent publications from the International Council for Research in Agroforestry, ICRAF, as well as from several other organizations around the world (for details, contact ICRAF, P.O. Box. 30677, Nairobi, Kenya). The productive and protective functions of agroforestry in terms of its relevance as an alternative to shifting cultivation in different ecological situations have also been examined recently in a contribution to FAO's Soils Bulletin series (Nair and Fernandes, 1983). Without going into the details, suffice it here to say that agroforestry can be adopted to mitigate some of the problems of land management in a variety of environments. It is, therefore, logical to examine the existing agroforestry systems and practices with a view to identifying the desirable characteristics of the promising ones and evaluating them as alternatives to resource-depleting shifting cultivation.

GLOBAL OVERVIEW OF AGROFORESTRY SYSTEMS AND PRACTICES

Agroforestry

Although agroforestry has variously been defined (see, for example, Agroforestry Systems, Vol. 1, pp. 7-12, 1982), it has generally been agreed that it represents an approach to landuse involving deliberate retention of trees and other woody perennials in the crop/animal production fields (Lundgren and Raintree, 1983; Nair 1983a, b). If we look at the existing landuse systems keeping such a broad concept of agroforestry in mind, we find that several of them can be considered to encompass the principles of agroforestry (Nair and Varghese, 1980; Nair, 1983c). ICRAF is currently undertaking a global inventory of such existing agroforestry systems and practices. The basic document that was prepared for the project included a preliminary overview of the situation in the developing countries indicating the most prominent examples found in the different regions. Some aspects of this document including the "System Overview Table" have subsequently appeared in a few scientific journals that featured detailed project announcements (see Agricultural Systems, 11 (1983): 191-194; Agroforestry Systems 1 (1983): 269-273; Biomass 3(1983): 241-245). Though based on the existing knowledge prior to the commencement of the formal survey of the project, that summary Table shows the diversity of agroforestry systems and practices.

Types of Agroforestry Systems

As pointed out by Torres (1983a), there can be several schemes for classifying the multitude of agroforestry systems. Thus, the criteria can be the types of woody components included, the role of the woody component in the system, the type of interaction between the woody and other components (spatial or temporal), the way in which the components are spatially arranged, and so on. But usually the first criterion in a classification scheme is the type of components involved in the system, and according to that there are three broad subdivisions: agrosilvicultural, silvopastoral and agrosilvopastoral.

The agrosilvicultural system combines the production of tree crops (forest-, horticutural-, or agricultural plantation-) with herbaceous crops, in space or time, to fulfill productive or protective roles within the land management systems. Examples can be hedgerow intercropping (alley cropping), improved "fallow" species in shifting cultivation, multistorey multipurpose crop combinations, multipurpose trees and shrubs on farm lands, shade trees for commercial plantation crops, agroforestry fuelwood production systems, shelterbelts and windbreaks and so on. The silvopastoral systems integrate woody perennials with pasture and/or livestock. Examples include animal production systems in which multipurpose woody perennials provide the fodder (protein bank), or function as living fences around grazing land or are retained as commercial shade/browse/fruit trees in pasture lands. The agrosilvopastoral systems, as the name implies, combine trees and herbaceous crops with animals and/or pastures. The use of woody hedgerows for browse, mulch and green manures and for soil conservation, the crop/tree/livestock mix around homesteads, etc. are good examples of this system. It is also a common practice in some places to have sequential patterns (integration in time) of an agrosilvicultural phase followed by a silvopastoral one so that initially trees and crops are established, and later on, the crops are replaced with pasture, and animals are brought in. Table 1 summarizes the primary nature of the role (productive/protective) of the woody perennial, the type of interaction (temporal/ spatial) between the major components and their spatial arrangement (mixed/zonal) in the system.

Field Examples

Information gathered by ICRAF for the earlier mentioned global inventory of agroforestry systems shows that there are several successful field examples of each of the subsystems and practices mentioned in Table 1, under a wide range of ecological conditions. The ICRAF survey collects and collates information pertaining to the functioning and dynamics of these systems, as well as analyzes their merits, weaknesses and constraints with a view to identifying research needs and extending the systems to other areas. Table 2 gives a summary account of some of the prominent examples of such agroforestry systems and practices and the woody species involved. The Table is not at all exhaustive; it is abstracted from the detailed information that is collected and stored at ICRAF.

Information on the agricultural components of the systems is also being gathered at ICRAF. The crops that are used in these systems are more or less the same in similar ecological regions in different parts of the world. For example, in the lowland humid tropics and other ecological regions of West Africa, Southeast Asia, and Latin America, cereals (maize, rice), tubers (cassava, yams) and legumes (beans, cowpea) constitute the major food crops and depending on the tree arrangement, extent of shade and other factors, one or the other species is chosen for a particular farm or field. in this context, the environmental adaptability chart for common agricultural crops suitable for agroforestry, prepared by Nair (1980), is relevant (Table 3).

Experimental and Potential Agroforestry Systems

Consequent to the awareness about the potentials of agroforestry, field research is now being undertaken on some agroforestry technologies in a few places in different parts of the world. Since agroforestry does not usually fall under the domains of the conventional agricultural and forestry disciplines, such trials are not commonly known by the name "agroforestry," and in many cases, they are handled by outreach or integrated programmes of institutions that are mandated to focus on a commodity, a group of similar commodities, or on an ecological region. Nevertheless, some of these efforts have already produced commendable results enabling researchers to transfer such technologies from research stations to farms. Examples of such experimental systems and practices which the author has visited or is aware of include the following:

i) crop combinations and other integrated production systems with coconuts and other plantation crops in smallholdings. Active work is being carried out at The Central Plantation Crops Research Institute, Kasaragod, Kerala, India (Nair, 1979; Nelliat and Bhat, 1979); Department of Minor Export Crops, Matale, Sri Lanka (Bavappa and Jacob, 1982); Rubber Research Institute of Malaysia, Kuala Lumpur (Wan Embong and Abraham, 1976), and other similar institutions.

ii) Agroforestry and mixed cropping experiments involving cacao, coffee, black pepper, rubber, guarana (Paullinia cupana) and others conducted at various places in northern Brazil by CPATU (Centre for Agricultural Research in the Humid Tropics), Belem, Brazil; CEPLAC (The Cacao Research Center in Bahia State of Brazil; experiments by EMBRAPA (Brazilian National Agricultural Research Organization) stations in Manaus and other parts of Brazil; CATIE (Tropical Agricultural Research and Training Centre), Turrialba, Costa Rica, etc. (De las Salas, 1979; Alvim, 1981; CPATU, 1982; Budowski, 1983).

iii) The alley cropping experiments at the International Institute of Tropical Agriculture, Ibadan, Nigeria. Alley cropping is a cropping systems where arable crops are grown in the interspaces (alleys) between rows of planted trees or woody shrubs, which are pruned periodically during the cropping season to prevent shading and to provide green manure and/or mulch to the arable crop (Wilson and Kang, 1981; Hartmans, 1981). Following the successful results obtained at IITA (Kang et al., 1981a, 1981b), the technology has received wide acclaim and critical attention (Torres, 1983b; Nair, 1983d) and similar trials have been initiated at a number of other centres in different ecological situations.

iv) Investigations conducted by the Central Arid Zone Research Institute (CAZRI), Jodhpur, Rajasthan, India, on the beneficial effects of Prosopis cineraria on the production of millets and other dryland crops in the arid regions of India (Mann and Saxena, 1980).

v) Agroforestry pilot projects like the "Project Agro-Pastoral" at Nyabisindu, Rwanda, where different technologies for integrated production in smallholdings with low levels of inputs are being tested and disseminated (Zeuner, 1981; Neumann, 1982).

vi) The enormous extent of effort and enthusiasm on fuelwood species (example: NAS, 1980) and the large number of research and development projects on fuelwood production in agroforestry systems.

vii) Research on the fodder producing trees and shrubs and silvopastoral systems in a variety of environments (Le Houerou, 1980; Torres, 1983c).

viii) Initiatives to create a global network for collection, preservation and improvement of germplasm of multipurpose trees and shrubs suitable for agroforestry in different situation (Workshop on Multipurpose Tree Germplasm organized by ICRAF in June, 1983, and the follow-up to that: 0. Von Carlowitz, ICRAF; field trials involving multipurpose trees at ICRAF Field Station, Machakos, Kenya by Nair et al. (1983)).

In addition to all these efforts and initiatives, there are also several possibilities for designing a large number of potential agroforestry technologies suitable for different ecological situations. For example, different plant combinations can be evolved by selecting the components from Tables 2 and 3 and combining them according to the desired needs and objectives as outlined in Table 1. Management considerations of such prototype technologies will become critically important, for which available information on these aspects will turn out to be extremely useful. Critical evaluations and compilations have recently been prepared on soil and soil productivity aspects of agroforestry (Mongi and Huxley, 1979; Nair, 1983d) and plant aspects related to agroforestry (Huxley, 1983). obviously, a considerable amount of thinking and planning has to go into developing each of such technologies and systematic research undertaken before recommending them for large-scale adoption.

FROM SHIFTING CULTIVATION TO AGROFORESTRY

The foregoing account of existing agroforestry systems and practices, as well as experimental technologies, indicates the spectrum of possibilities for designing appropriate alternatives and improvements to shifting cultivation in a variety of situations. The input requirements and output patterns of these innovations will obviously be different and so their level of acceptance and adaptability by the shifting cultivators will also vary accordingly. All of these alternatives involve woody and usually multipurpose species in intimate associations with other components. The expectation from such combinations is that the soil enriching functions of such woody species will produce results that are, to some extent, similar to the soil improvement that takes place during the fallow period in shifting cultivation. Nair (1983d) has critically analyzed the soil improvements that can reasonably be expected in such agroforestry associations.

A point of considerable significance in this context is the intensity of labour involved in such improved systems vis-a-vis shifting cultivation. Almost any meaningful alternative to shifting cultivation will essentially be more labour-intensive and landintensive (consequent to increasing population and accompanied subdivision of holdings) as compared to traditional shifting cultivation. Historical evidence on the evolution of farming systems shows that traditional farmers tend to resist the adoption of more landand labour-intensive technologies as long as less labour-intensive alternatives are able to satisfy their production objectives (Raintree, 1983). However, if appropriate labor-intensive technologies are available to absorb the increased labour per unit area, the reduced area can be made to support a much increased rural population as evidenced by studies on alternate labor-intensive technologies in subsistence farming systems and the pattern of adoption of such technologies in a variety of environments. For example, Nair (1979) found that improved crop combinations with coconuts could enhance levels of output so that a one hectare area of coconut garden could sustain an average family at "reasonable" levels of subsistence in the impoverished coconut growing areas of India. Similarly, studies on the home gardens of Java in Indonesia provide a good example of how a very small piece of land can support a relatively large number of people (Wiersum, 1982). Therefore, it can be surmised that the high labour-intensive nature of agroforestry alternatives will not be a deterrant in the long run to their adoption by the farmers.

Table 1. The role of woody perennials, their arrangement and interaction with other components in some common agroforestry systems.

Table 2. * Field examples of a few common agroforestry systems and practices in the tropics and sub-tropics and some of the woody species involved.

* Table compiled from the information being gathered and stored at ICRAF by Mr. Erick M. Fernandes for the Agroforestry Systems Inventory Project.

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. Agrosilvicultural systems (continued).

Table 2. II Silvopastoral systems (continued).

Table 2.
II- Silvopastoral systems (continued).

Table 2.
III. Agrosilvopastoral systems

Table 2.
III. Agrosilvopastoral systems (continued).

Table 3. General grouping of the selected crops according to their adaptability to different ecological regions in the tropics.

¹PERHUMID-SUBHUMID : areas with 0-4 dry months and more than 1200 mm rain per year
²SEMIHUMID-SEMIARID : areas with 5-8 dry months and 500-1200 mm - rain per year
³SUBARID-PERARID : areas with more than 9 dry months and less than 500 mm rain per year
A month is considered 'dry' when the potential evapotranspiration is more than the precipitation received during the month.

*Adapted from Nair, P.K.R. (1980). Agroforestry Species: A Cropsheet Manual. 336 p.

The progression from traditional shifting cultivation to intensive agroforestry can be expected to take place gradually but at a steadily increasingly labour intensity and landuse intensity factors. Initially, a taungya type of intercropping between rows of trees that are also periodically harvested for firewood will meet the farmers immediate needs for food and wood products. But with an increased population pressure, there will be a hedgerow intercropping cycle with "partial" or shortened rotations of fallow in subdivisions of the farms. Eventually, with still higher population pressure, permanent hedgerow intercropping and subsequently continuous multistory combinations will follow. Thus, the temporal association of crops and trees in sequential cycles (shifting cultivation) can ultimately be replaced by spatial associations and temporal arrangements of crops and trees in vertical dimensions (agroforestry) through a succession of acceptable management practices.

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