An e-publication by the World Agroforestry Centre
METEOROLOGY AND AGROFORESTRY
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An e-publication by the World Agroforestry Centre |
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METEOROLOGY AND AGROFORESTRY |
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section 3 : regional examples Agroforestry systems for the cerrado region of central Brazil: potentials and constraints M. Haridasan
Laboratorio de Ecologia, Departamento de Biologia Vegetal Abstract The Cerrado region of central Brazil extends over 180 million ha and is characterized by a prolonged dry season which limits agricultural production. Less than 10 million ha were under field crops until recently whereas more than 100 million ha were under cultivated or native pasture. Irrigation is not yet widespread. Besides the long dry season extending from May to September, wet season dry spells, known locally as veranicos, also limit the yields of field crops. The water storage in the surface layers of the soil is often insufficient to meet the evapotranspiration demand of shallow rooted field crops because of the low waterholding capacity of the latosols and the very deep water tables. Deep well drained latosols which account for about 50% of the Cerrado region also present very severe limitations of aluminium toxicity, phosphorus deficiency and low base saturation. Soil erosion is a severe problem in most areas because of soil compaction and reduced infiltration rates resulting from the use of heavy machinery and overgrazing. Agroforestry is not yet a common practice in the region whereas extensive areas are utilized for eucalyptus and pine plantations. The potentials for agroforestry systems in the Cerrado region are discussed in the present paper. Well-planned agroforestry systems in central Brazil should minimize the risks of
Introduction The cerrado region of central Brazil extends over more than 180 million ha, accounting for nearly one-fifth of the total area of the nation. The region is heterogeneous in terms of potential for agriculture, pasture management, silviculture and agroforestry systems but is often considered to be a savanna-type ecosystem. It is interesting that the development of the Amazon region of Brazil and the possible consequences of destruction of the native vegetation of evergreen tropical humid forests there are being discussed at national and international levels with great alarm whereas the destruction of the equally fragile ecosystems of the cerrado region continues without ample discussions on viable alternatives of safe management of natural resources like soil and native vegetation (Alvim and Silva 1979; Goodland and Irwin 1975). Intensive agriculture in many parts of the cerrados is a very recent phenomenon. Since the region of cerrados is not an administrative unit, it is very difficult to obtain statistics of economics, population growth, agricultural production and productivity for the region as a whole. Any generalization of policy recommendations is also difficult because of the enormous size, variations in climate, soils, vegetation and geomorphology, and uneven pattern of population growth. However, in the present paper I shall examine the possibility of agroforestry management in the region in very general terms.
Climate The cerrado region may be divided into five principal subregions on the basis of climatic variations (Azevedo and Caser 1979):
Subregions 4 and 5 occupy relatively very little area. Azevedo and Caser (1979) subdivide these subregions into forty smaller geographical units on the basis of geomor-phological characteristics. Detailed data on rainfall, temperature, evapotranspiration and radiation can be found in Hargreaves (1976) and Golfari et al. (1978). Johnson (1982) and Reddy and Amorim (1984) discuss the paucity of climatic data for the region and suggest modifications for calculations of potential evapotranspiration and radiation for the region, taking into account altitude, latitude and longitude for the different stations. Further refinements of the models can be achieved only when more careful measurements are available for longer periods. Probably the least variable component is the average monthly temperature which oscillates around 20 °C in the core region. Maximum temperature oscillates around 27 °C and minimum around 16 °C. Day length and radiation are not limiting factors for plant growth during any time of the year. For example, mean monthly values of solar radiation is always above 15 MJ m-2 d-1 in Brasilia with maximum values exceeding 18.5 MJ m-2d-1 The most limiting factors for agricultural production are the variations and uncertainties in the rainfall distribution. Wolf (1977) discusses the occurrence of dry spells during the rainy season in Brasilia. These wet season dry spells, known locally as 've-ranicos', may last over three weeks once in seven years. There is a 50% chance that the longest dry spell in any year will be 14 days or longer and a 15% chance that the dry spell will exceed three weeks. Thus, even if the total rainfall during the season is satisfactory, crop failure due to water stress is a common occurrence in the cerrado region. In shallow rooted crops like soybeans, evapotranspiration may be reduced from a high value of 4 to 5 mm/day during the first week of veranico to 1 to 2 mm/day by the end of the third week, mainly because of low water potentials in the top layers of the soils (EMPBRAPA1981, p. 64-65). Monthly averages of rainfall do not bring out the variations in precipitation but averages for 10-day periods might be sufficient to indicate periods of water stress (Wolf 1977). Deep rooted cerrado trees and shrubs, however, show no apparent signs of water stress during these dry spells.
Soils of the cerrado region do not fall into any distinct category as different from soils of other climatic regions of the country. Latosols are the most extensive soils in the cerrado region. These are, as a rule, well-drained very deep soils with a clayey texture and very little horizon differentiation. The most interesting feature of these soils probably is the very fine microaggregate structure of the subsoil (B) horizons, which, in situ, present a massive appearance. The microaggregates are very water-stable and make these soils highly permeable. Infiltration rates measured under native vegetation generally exceed 15-20 cm/h. The surface (A) horizon often has a stable granular structure under native vegetation but, devoid of a vegetation cover, is susceptible to compaction and erosion by water. Once the surface layer is eroded, the massive B horizons succumb very easily to formation of very deep U-shaped gullies. Under native vegetation the bulk density of well-drained soils is often less than 1 g cm -3 because of very intensive termite activity. Deforestation using heavy machines; and cultivation, as well as grazing by cattle, generally lead to soil compaction and reduced infiltration rates. Also, water retention capacity is reduced because of the destruction of the original highly porous structure. The water retention capacity of cerrado latosols is very low (Wolf 1977; Lopes 1983; EMBRAPA 1982). This is attributed to the nature of the clays and the microaggregate structure which makes the soils behave as if the texture were more sandy. The very low water retention capacity makes the effect of wet season dry spells very severe. Once the soil becomes unsaturated, hydraulic conductivity of the soil decreases sharply (-EMBRAPA 1981, p. 71-72) and shallow- rooted crops will not have enough water flowing to the root zone from deeper layers with high water content. Most of the discussions in the literature focus attention on fertility aspects (Lopes and Cox 1977; Goedert 1983) and response of crop plants to fertilizer application and liming. The most serious impediment to root growth in lower layers of the soil profile is probably deficiency of calcium (Ritchey et al. 1980,1982) since calcium is not translocated to growing root tips if it is not available in the rhizosphere of growing rootlets. However, native shrub and tree species have very deep roots which help them extract water even during the dry season when top layers of the soil profile hold very little water. Agronomic experiments during the last decade (EMBRAPA 1979,1981,1982) have shown that most of the crop plants respond well to liming and fertilizer application in the cerrado soils. However, the economic aspects of liming and fertilizer application do not seem to have received the attention the problem merits. Also lacking is definite proof in many cases that it is the applied nutrient that is responsible for better growth and higher yields. It is not just one element that is lacking in cerrado soils. Response to liming could be due to higher availability of magnesium (Bataglia et al. 1985); that attributed to phosphorus could also be due to higher availability of calcium from superphosphate. Until we have more information from these experiments on nutrient uptake by analyzing plant tissues we cannot determine responses involving different nutrient elements. Until then any economic analysis of the fertilizer recommendations will not be very meaningful. For example, at least in the case of two eucalyptus species, soil acidity and high exchangeable aluminium levels do not seem to pose any limitations, if other nutrients like phosphorus, calcium and magnesium are adequate (Haridasan 1985). Managanese and iron toxicities do not seem to pose serious problems in well-drained soils but may become crucial in water-logged soils. Micronutrient deficiencies may have to be corrected in intensive agriculture when high doses of fertilizers and lime are applied. Goedert (1983, p. 424-425) summarizes succinctly the need for basic research in soils and plant physiology to understand better the processes of nutrient uptake and crop growth in these nutrient-deficient soils. The other classes of soils which occur in the cerrado region include podzolic soils, terra roxa soils, cambisols and waterlogged soils. Since there is no well-defined hierarchy in the Brazilian system of soil classification it is difficult to place these soils in other soil classification systems. Equivalent class names in other systems of classification such as that of Soil Taxonomy and FAO/UNESCO in the case of soils of the Federal District in the core region of the cerrados are indicated in Table 1. One of the main limitations is the lack of definition of criteria for a hierarchical classification. Many surveys utilize native vegetation or slope classes as criteria for subdivision of higher order categories without any definition of the variation in soil properties among different subclasses (Haridasan 1988). There is very little information available on the moisture and temperature regimes of these soils to place them correctly in Soil Taxonomy. In general, most of the well- drained latosols have an Ustic moisture regime.
The cerrado region comprises of widely varying physiognomic forms of vegetation, which vary from tall closed canopy forests to grasslands devoid of any trees and shrubs. Eiten (1972) provides an excellent review of existing information on these physiognomic forms. The most common of these formations is an open tree and scrub woodland known locally as the cerrado, sensu stricto. The question of comparing the cerrado ecosystem(s) with other similar tropical ecosystems, especially the so-called grasslands and savannahs, always involves controversies and myriads of conflicting opinions as to the definition of different physiognomic forms of vegetation (Eiten 1978, 1986). Botanists have often worried about providing details of species composition and phyto-sociology but very little information is available regarding the adaptability of the cerrado species under different edaphic and climatic conditions. Interestingly, agronomists and soil scientists have seldom participated in this discussion, leaving it entirely to botanists to argue about the adaptive strategies of native plants. The only welcome exceptions were probably the surveys conducted by some British teams (Askew et al. 1970a, 1970b, 1971; Ratter et al. 1977,1978). Even in their work the only information provided is on variations in physiognomy and species composition of vegetation communities in relation to soil fertility and other edaphic factors such as the occurrence of water table. The role of climate, edaphic factors such as soil depth, water regime and soil fertility, and fire in the origin and maintenance of the cerrado, sensu stricto, is discussed by Eiten (1972). The consensus at the moment is that cerrado, sensu stricto, is more a consequence of the dystrophic nature of the soils on which they occur than a consequence of the climate (the long dry period) and intermittent fires which are common in the region. The cerrado, sensu stricto, occurs exclusively on deep, well- drained dystrophic soils. When the soil becomes shallow as in the case of cambisols on slopping terrain the trees and shrubs become sparse to give rise to a more open vegetation form known locally as 'campo sujo'. When the soil is waterlogged permanently or at least during three to four months of the year the vegetation form is a pure grassland, called 'campo limpo'. Tall closed canopy forests occur in different situations such as along streams in valley bottoms (gallery forests), on well-drained mesotrophic soils (semi-deciduous forests), on calcareous soils (deciduous forests), and on dystrophic soils (cerradao). There is no consensus of opinion as to the contribution of edaphic factors in the formation of 'cer-radoes' on dystrophic soils alongside more open form of cerrado when both occur on equally poor soils. Ratter et al. (1977,1978) discuss the species composition of forests on dystrophic and mesotrophic soils. Some species occur only on dystrophic soils; others only on mesotrophic soils. And there are species that are indifferent to soil fertility. Physiological basis of this preference of soils in native species has not been investigated in any detail yet (Haridasan and Araujo 1987). Goodland (1971b) suggested that cerrado-native species were adapted to high levels of available aluminium in the soil and exhibited sclerophyllous nature not only because of low fertility of the soils but also due to aluminium toxicity. Haridasan (1982) reported that several species of the cerrado vegetation accumulate aluminium in large quantities in their leaves but high levels of aluminium in the leaves of these plants are not associated with low levels of other cations. Besides high levels of aluminium in the soil, what limits plant growth in these soils are the extremely low levels of phosphorus and exchangeable cations, calcium, magnesium and potassium. Table 1 Classification of the soils of the Federal District in the cerrado region of Brazil
The more optimistic estimates put the extent of land suitable for intensive mechanized agriculture in the cerrado region to be more than one-third of the total geographic area (Goedert 1983). However, intensive agriculture in many parts of the region is a fairly recent phenomenon. The area under field crops is less than 10 million ha (Table 2). More than twice this area is under cultivated pastures. The area under native pastures is estimated to be nearly 120 million ha which accounts for almost 60% of the total land area of the region. Most of the area cultivated are under monocropping. Crop rotation is common. However, agroforestry or agrisilviculture is not a common practice. Until intensive agriculture with field crops like soybeans, maize, wheat and sorghum was introduced, a common practice was to grow upland rice for two or three years after deforestation and burning and then use the land for pasture. Table 2 Land use in the cerrado region of Brazil
There are only very few systematic, long-term studies reported in the literature on the decline in productivity of the cerrado soils. Research on many aspects of soil management began only about 25 years ago at the Instituto Agronomico de Campinas and later at the Centro de Pesquisa Agropecuaria dos Cerrados in Brasilia (Goedert 1983). It is estimated that less than 10% of the total cultivable area in the cerrado region has mesotrophic soils where soil fertility is not a limiting factor. Most of this land is already under cultivation. Therefore any expansion of area under cultivation would essentially be in dystrophic latosols. Leite and Furley (1985) who studied one of the settlement colonies of small scale farmers concluded that low productivity of traditional crops was one of the detrimental aspects that caused the project to fall short of its crop and livestock production targets. Evaluating the success of the Sagarana Colonization project which started settling farmers in 1973, these authors reported that the productivity of the traditional crops such as rice, beans and maize was below the targets established at the beginning of the project and none of the fruit crops like citrus, mango, guava and avocado was ever cultivated. The original assumption was that the farmers would utilize an integrated management system involving liming and fertilizer application and soil conservation measures such as contour planning and terracing. The original target for establishing pastures was also not fulfilled because of the low productivity of the pastures. One of the most serious land management problems in the cerrados is the degradation of pastures due to overgrazing and low primary productivity of the ground layer due to poor soil fertility. The prolonged dry season adds to the constraints, limiting stocking rates to 0.2 animals ha" . Once the land has been under native pasture for 15 to 20 years many areas are simply abandoned because it is not economically viable under the present set up to continue to raise beef cattle. Land recuperation in these areas is a very severe challenge because of the impoverishment of the surface layers of the soil not only from overgrazing but also because of soil erosion damage. Invasion of these areas by native species to form a secondary forest vegetation is often a very slow process unlike in small holdings which are abandoned by settlers after deforestation and cultivation for two or three years in the Amazon region (See for example, Leite and Furley 1985). An important aspect of the land use pattern in Brazil is the size of individual land holdings. Nearly 45% of the total land area in the country is accounted for by individual holdings of more than 1000 ha (Table 3). Another 35% of the area is accounted for by holdings of 100-1000 ha. Only less than 2.5% of the area is owned by individuals who possess fewer than 10 ha though they account for more than 50% of the total number of individual properties. Table 3 Size of individual land holdings in Brazil in 1980 (IBGE,1980. Censo Agropecuario do Brasil).
The population in the cerrado region was estimated to be 15 million in 1970 and nearly 21 million in 1980, with a 3.3% annual growth rate during the last decade (Goedert 1986). More than 60% of this population lived in urban areas in 1980. In the early 1970s less than 50% of the population lived in urban areas. With migration to urban areas increasing while more area is being brought under cultivation, availability of skilled labour for agriculture in rural areas will be scarce in the future. This might increase the need for mechanization and lead to faster deterioration of soil in cultivated land. The reality is that the big farmers, at least for the present, are not concerned about long term damage that can result from the use of heavy machinery and excessive quantities of fungicides, pesticides and herbicides. Soil conservation and preservation of natural ecosystems, especially of native plant species that might be of economic use in the future, seem to be only concepts idealized in many federal laws and regulations. Adverse effects of indiscriminate deforestation in the catchment areas of big rivers is always evident in frequent flooding of low-lying areas during the monsoon season on the one hand and the shortage of water in the reservoirs of major hydroelectric projects in the country during the dry season on the other hand.
The most interesting aspect of agroforestry systems is that it was once the essence of subsistence agriculture with very low inputs, especially in the tropics. Intensive monoculture involving mechanization and heavy input of fertilizers and other agrochemicals following the model of temperate zone agriculture is a fairly recent phenomenon, especially in the more extensive oxisols and ultisols. In the case of Brazilian cerrados, it is only in the last several decades that intensive monoculture has been replacing extensive pastures. Some of the peculiarities to be considered with regard to any discussion of possible agroforestry in the region are the following:
What this means is that there is very little change possible in the existing pattern of land use without the government advocating it. At present there is no practice of any agroforestry system worth mentioning in the cerrado region unlike in other regions of the country such as the ones described by Alvim and Nair (1986) in southern Bahia; by Johnson and Nair (1986) in the northeast; and by Baggio (1986) in the south. I shall therefore discuss the potentials of agroforestry systems in the cerrados with emphasis on overcoming important natural limitations of intensive agriculture in the region.
As mentioned earlier one of the more serious limitations in agriculture and pasture management in the cerrado region is the occurrence of wet-season dry spells which may last from a few days to more than three weeks. These dry spells cause severe damage to field crops and grasses which have shallow root systems because they occur when evapotranspiration demands are high (Fageria 1980; Espinosa 1979; Garrido et al. 1979). Though there is often sufficient water lower in the profile, surface soil layers have very little water because of low water retention capacity. Tree species are generally capable of utilizing the subsoil moisture unlike the shallow-rooted crops and grasses. It is only within the last few years that the Federal Government announced plans to implement large-scale irrigation schemes in the cerrado region to increase agricultural production. However, it is unlikely to be a universal practice in the immediate future because of limited water availability. It is estimated at present that the potential for irrigation in the cerrados is only about one million ha. Wet-season dry spells could be very damaging if they coincide with critical growth stages such as flowering. The most serious problem in this regard is the adoption of monocropping systems by the farmers mainly because no alternative systems are known to them. Suitable agroforestry systems should offer some security against total loss of income, especially in the case of small farmers. Selection of suitable perennial crops tolerant to water stress and adapted to low soil fertility and high soil acidity could be one of the useful strategies in this regard. Traditional fruit trees like mango, citrus and guava as well as other native species which could be exploited on a commercial scale should be one of the options. Settlers in new colonization projects with relatively little experience in farming should find this option more secure than risking everything in shallow-rooted field crops. Besides guaranteeing an alternative source of income, one of the possibilities that should be exploited in agroforestry systems for the cerrado region is minimizing evapotranspiration demand by providing shade or reducing wind velocity. Since the low water-holding capacity of the cerrado soils is one of the limiting factors contributing to crop failures during wet season dry spells, improving the water retention characteristics of these soils should be one of the aims of better management systems. Long-term crop rotations with fast growing trees species which could increase the organic matter content of these soil should eventually help increase the water holding capacity of these soils and thus minimize the risk of wet-season dry spells. In spite of the serious lack of fodder in native pastures of the region during the long dry season, very little has been done to utilize alternative sources of forage to supplement the limited grass supply. Silvopastoral combinations involving forage shrubs and trees should be a viable practice in this respect.
Avoiding deterioration of pastures The main factors contributing to the complete deterioration of pastures within ten to fifteen years are poor soil fertility and overstocking. Any viable alternative to 100% utilization of such lands for animal husbandry on a long-term basis should involve fallowing the land periodically. Fertilizer application and liming are expensive options to increase the productivity of native pastures because the potential response of native grasses to fertilizer application is as yet unknown. In such cases economically viable management systems might incorporate forestry or fruiticulture alternating with animal husbandry. With ten- to fifteen-year cycles, degraded pasture lands might recover organic matter content and nutrient status if fast-growing tree species which would furnish plenty of leaf litter could be utilized. Grass-legumes mixtures are advocated in the cerrado region on the following grounds:
One of the serious handicaps in adopting this system is the high cost of establishing cultivated pastures in the cerrado region. Large areas of the region are expected to remain as native pastures for many years (Couto et al. 1983). One of the viable alternatives should be the adoption of agroforestry systems involving legume trees with the same objectives but with the additional advantage of better soil conservation. Use of leguminous nitrogen-fixing species and those with associated micorrhyzae capable of solubilizing phosphorus should have the greatest potential in this regard (Faria et al. 1984; Lopes et al. 1983; Nair et al. 1984). Faria et al. (1984) made an extensive search for active nitrogen-fixing root nodules amongst Brazilian forest legumes and reported seven new nodulated species, including two new nodulating genera from Caesalpinioideae; 18 new species from Mimoisoideae; and 30 new species, including four new genera, from Papilionoideae. All these species have the potential for use in agroforestry systems in the cerrado though some of them are not native to the region. One important aspect that should be investigated in this connection is the adaptability of native species with economic potential in dystrophic acid soils. It should be borne in mind that the predominant native vegetation of the cerrado is a consequence of poor soil fertility and not of climate alone. Other than the reports of Ratter and co-workers (1971, 1977, 1978), there is very little information in the literature on the distribution of cerrado species in different soils. Recent reports (Araujo and Haridasan 1988; Haridasan and Araujo 1987; Machado 1985) have shown that resistance or tolerance to high aluminium levels in the soil may involve more than one mechanism. While some aluminium-accumulating species occur only a dystrophic acid soils, others occur only in mesotrophic soils with near-neutral pH. A few occur on dystrophic as well as mesotrophic soils but grow better on mesotrophic soils. Besides furnishing foliage for animal feed and improving soil fertility, another important use of trees in pastures is to provide shade and shelter for animals, especially on hot dry days. In many cases, farmers leave isolated trees in the middle of pastures, which is not an ideal solution. This practice often creates the problem of aggregation of animals. Also, individual isolated trees succumb more easily to strong winds. Another practice is to provide isolated patches of trees, especially around artificial lakes which provide drinking water. A better solution for providing shade and shelter for animals, at the same time providing forage and helping in soil conservation, would be to develop silvopastoral systems with overstorey tree species and understorey fodder species. Many species of the native tree vegetation such as Taipirira guyanensis, Copaifera langsdorfii, Callisthene major, Siphoneugenia sp., Hymenaea stigonocarpa (-jatoba), Dipteryx alata (baru), and Plathymenia reticulata have the potential to be used as shade trees (Machado, personal communication). Exhaustive lists of indigenous tree species that can be used in agroforestry systems are easy to compile but experimental evidence is yet lacking to make any definitive recommendations for farmers. For example, several species which occur in the gallery forests in the Federal District have the potential for commercial-scale exploitation.
Soil erosion is a severe problem in the cerrado region. Many publications erroneously state that soils of the cerrado region are not easily erodible. Sheet, rill and gully erosion pose severe problems in the cerrado soils because rainfall intensity is generally very high. The problem is worsened by the use of heavy machinery in latosols which after compaction loses its originally-high porosity and infiltration capacity. The fact that the soil is left without adequate vegetative cover at the end of the long dry season makes the soil extremely vulnerable to early torrential rains. The problem becomes more severe when Class IV to VIII lands are left without any vegetation cover after fire or deforestation to utilise available wood for charcoal production. Though existing laws prohibit destruction of gallery forest along rivers and streams in valley bottoms, indiscriminate deforestation of such vegetation is very common leading to not only erosion and increased runoff during the wet season but also to the drying of the streams in the dry season making little water available to cattle. Suitable agroforestry systems should therefore aim at not only conserving soil where it has not yet been degraded but should shift the emphasis in many cases to recuperation of degraded soils. Most discussions on agroforestry systems usually depend on references to publications from elsewhere to justify the possibility of utilizing exotic species for such purposes. What should be done in the cerrado region is to exploit the possibility of utilizing the native species which are adapted to the climate and low soil fertility. It is well established that the cerrado tree and shrub species have extremely deep root systems capable of utilizing subsoil moisture during the dry season and have several adaptive strategies to resist fires which are frequent in the region. The main forest plantations in the region are eucalyptus and pine. Because of the present economic conditions in the country, indiscriminate destruction of the native vegetation and planting of eucalyptus and pine were encouraged. The long term effects of repeated cultivation of eucalyptus and pine are still unknown but depletion of soil fertility and accelerated erosion, especially on Class VI to VII lands are certain consequences. One way to avoid total deterioration of such lands would be to develop suitable covercrops in such plantations and follow fallowing or crop rotations with tree crops which help recuperate soil fertility, for example by nitrogen fixation. Another viable alternative would be to think of agrosilvopastoral systems with multiple objectives if we should conserve natural resources of the region. Such arguments apply not only for the conservation of soil resources but also for the conservation of genetic resources of native vegetation as well as native fauna. The extinction of many animal and bird species in the region are often attributed to large-scale eucalyptus and pine plantations.
One of the most serious social problems in Brazil is the very low income of rural families who do not own any land but work on the farms. Even those who own some land and those who receive land from the government as a consequence of agrarian reforms often abandon the land after one or two crop failures. This happens often because of low inputs such as good quality seeds, fertilizers and pest and disease control. Often the farmers have no income in such cases because they depend on monocultures. After deforestation, they cultivate rice or other field crops for one or two years and then abandon the area to fallow or pasture. One of the serious consequences of such irregular productivity of cerrado soils is the abandoning of rural lands by small-scale farmers who migrate to urban centres. Furley and Leite (1982), for example, state that 50 families out of 208 who had received between 65 and 240 ha of land under the Sagarana colonization project abandoned their property within the first couple of years. They could not cope with officially-established targets for land clearing, planting of crops and repayment of loans. Diversification of crops and adoption of suitable agroforestry systems should provide a better chance of success in such cases. The development of agrosilvopastoral systems in such cases should be based on the utilization of available family labour throughout the year providing full-time employment but at the same time avoiding overburdening. Small-scale animal husbandry is one of the possibilities to be considered in this regard in agroforestry systems in the cerrados, besides options such as apiculture and inland fisheries where the facilities exist.
It is interesting that during the review of literature for writing this article, I encountered more articles on the possibility of agroforestry in the Amazon region than in the cerrados (for example, Hecht 1982; Eden 1982). The main limitation for the adoption and development of agroforestry systems in the cerrado region seems to be the lack of planning and forethought on the part of government agencies. The need for soil conservation on a long-term basis and welfare of rural families seem to be ideals advocated only on paper. The emphasis on monocropping and intensive agriculture in the region is in many ways artificial, sustained only by the eagerness of the government to support export-oriented crops with no concern about soil and water conservation or environmental protection. There is no careful planning in the management of forests or pastures in the cerrado region. There is no replanting in degraded lands and there is no attempt to replenish the stock of felled forests. Eucalyptus and pine plantations are intended only to furnish wood for industrial purposes and are monopolies of large firms. Some of the existing models can serve successfully for small farmers who may get to own land as a result of the proposed agrarian reforms (Furley and Leite 1982), Agroforestry should provide viable alternatives to existing models in such cases. Yet another argument in favour of agroforestry systems in such cases is that the possibility of intensive agriculture does not exist because:
There has been no serious attempt to evaluate the potentials of agroforestry systems in the cerrado region. One of the serious handicaps seems to be that none of the more prestigious agricultural colleges in the country is located in the cerrado core region. Post-graduate courses in agronomy, soil science, animal husbandry and forestry should be encouraged in different universities in the region if new farming systems are to be experimented with. Research centres of the federal agricultural organization (EM-BRAPA) are geared to attend research needs of individual crops; and, in some cases like the CPAC, to specific needs of the region. However, there is very little attempt to try novel ideas. As mentioned earlier, there are several native species which have the potential for utilization in agroforestry systems. There are many fruit trees that have the potential for commercial exploitation. Herringer and Ferreira (1972,1973a, 1973b) list several of these species. However, very little information is available on the agronomic aspects of these plants. Incorporation of these in agroforestry systems would warrant agronomic research on the following aspects:
There are no worthwhile attempts made to utilize native species in reforestation or agroforestry systems at present though there are isolated suggestions regarding the utility of several native species. For example, Escuder (1980) reports that leaves of many tree and shrub species such as Kielmeyera coriaceae, K, obtida, Ouratea hexasperma, Syagms spp., Palicouria rigida, Borreira spp. and Didymopanax macrocarpum are common in the diet of sheep. Castro and Junior (1984) found that Dispyros hispida, Ouratea hexasperma and Byrsonima coccolobifolia foliage was consumed in great quantities and Dalbergia violacea, Blepharocalyx suaveolens, Erythroxylum tortuosum, Davilla elliptica and Styrax ferrugineus leaves in smaller quantities, especially during the dry season. Utilization of these species to supplement the ration of sheep and of other tree and shrub species to supplement the ration of cattle and goats are possibilities that should merit attention in the cerrado region.
Whatever the prospects for agroforestry systems in the cerrado region, no progress will be possible until the philosophy of conservation of nature — soil, native vegetation, regional fauna and environmental quality — is accepted by the community. This dilemma is well expressed in a recent publication of the Ministry of Agriculture (Downes 1983) regarding the necessity for institutionalization of soil and water conservation in the country. Once this philosophy is accepted by the government and the farmers, adoption of agroforestry systems is only the next logical step because some kind of multiple use and periodic fallowing of agricultural land seem to be a must in tropical oxisols. The present outlook that Brazil still possesses land that can be yet brought under intensive mechanized agriculture just doesn't seem right if land deterioration is not to be our goal.
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