Crops and boundaries: manioc at its meridional limits in South America *.
Dos zonas y dos limites configuran la frontera espacial del cultivo de yuca o mandioca (Manihot esculenta) en Brasil, Uruguay y Argentina. Rendimientos, factores del medio ambiente, influencias culturales y conocimientos agronomicos se reunen para fijar el alcance meridional hasta la latitud 31[grados]48' S. Al explicar la distribucion de yuca se destacan las trayectorias culturales brasilena y guarani hacia al sur y el fotoperiodo de dias mas largos que influye en forma negativa al desarrollo de la raiz haciendo inutil su cultivo. Sin embargo, los avances geneticos pueden resultar en una nueva geografia.
Two border zones and two boundaries characterize the spatial edges of this cultivated plant in Brazil, Uruguay and Argentina. Production data, biophysical factors, cultural in fluences and agronomic understandings are brought together to set the southern reach of manioc (Manihot esculenta) at 31[grados]48' S. The southward thrust of Brazillan and Guarani cultural influences and the increasing daylength which atrophies manioc root development are two major factors to explain the borders. However, future genetic advances could push those limits beyond those now in place.
Boundaries instinctively intrigue geographers who constantly deal with discontinuities in every map they make of read. A crisp line on the cartographic representation of a distribution immediately sparks interest in the logic of the categories used to define it, the appropriateness of the line's particular spatial placement, and how boundaries are to be understood. Those questions lead to ah appreciation that the meaning of discontinuity in a specific place is hardly ever as straightforward as it seems to be in the abstract.
The distributional limits of a cultivated plant represent one kind of boundary. As highly manipulated biological organisms, most crop plants cannot survive without sustained human involvement. Their evolution represents selections for yield, taste, appearance and/or resistance to pathogens. Cultural preferences, together with economic factors of satisfactory yield, assured market and/or favorable price, guide decisions that determine where a crop will be found. But yield performance is also a function of certain tolerances set by the plant's much longer period of environmental adaptation as a wild-growing predomesticate. Cultural and physical factors interact to account for the regional concentrations and limits of cultivation of these organic artifacts.
The few crop boundary studies that have been made in Latin America have focused on the altitudinal zonations of highly telescoped climates. In the Central Andes, the vertical discontinuities in a succession of crops reflect peasant awareness and sensitivity to environmental differences and how they can be used to minimize risk (Gade, 1975; Brush, 1977). By contrast, crop boundaries stretched latitudinally are less readily decipherable in the visible landscape. North/south biophysical factors and cultural influences are more attenuated in setting limits than are those in mountains. To examine the complexities of agricultural borders, one crop, manioc (Manihot esculenta Crantz) is probed at its southern margins of distribution in Brazil, Uruguay and Argentina. Its name in all three countries --mandioca-- suggests a shared culture history more than a common language (Gade, 2002). A transnational and transcontinental perspective on manioc elicits larger principles about an aspect of cultivated plant distributions in general. Juxtaposing micro-level observations with macro-level information of one particular crop, including comparative observations from other continents, open to view spatial and ecological complexities that overule the simplistic understanding of crops that dominate the textbooks and lecture halls. The holistic approach might also be useful in scrutinizing the geography of other crop plants.
Manioc as Plant and Product
The fundamental advantage of this shrubby plant of tropical South American origin is its ability to produce abundant calories per unit area on relatively poor soils without the need to follow a tight harvest schedule (Figure 1). Furthermore, little work is needed lo successfully grow this plant. These advantages place manioc among the top five food plants in the world in terms of calories produced. However, because freshly harvested roots have a Iow value to weight ratio and high perishability, they must be processed into a more durable edible forro to enhance their place in human diet and commerce.
[FIGURA 1 OMITIR]
The most problematic aspect of manioc use is the continuum of toxicity in its roots. Al one time, manioc was neatly divided into "sweel" (i.e. non-poisonous) and "bitter" (i.e. poisonous) varieties which for many years became the justification for putting them into two different species: Manihot dulcis and M. utilissima. By the mid-twentieth century, that division was untenable, for under certain conditions, such as kind of soil in which they grow or period of time kept in the ground, some cultivars classified as sweet can transmute into bitter. Moreover, all manioc was found to contain at least some hydrocyanic acid (HCN) in the form of cyanogenic glucosides. Roots with HCN levels below 10 mg per 100 grams of pulp are generally considered to be harmless. Recognition of this toxic continuum led to a revision of the scientific nomenclature intojust one species, Manihot esculenta. However oversimplified, the sweet/bitter polarity is still recognized asa useful distinction in both English and Spanish ("dulce" vs. "amarga"). In Portuguese, the 'wild' (Mandioca brava) and 'tame' (Mandioca mansa) is used, although in Southern Brazil, non-poisonous manioc is commonly referred to as aipim.
The practical implications of this continuum are that while manioc cultivation requires relatively little care, farmers must learn to distinguish between the cultivars in this continuum and recognize which ones change their toxic character. Mistakes in identification can lead to tragedy. Ingestion of high levels of HCN causes vomiting, dizziness and occasionally death. Humans are more susceptible than domestic animals. Manioc processing has as its primary goal reducing the glucosides in the edible product to the point where it is safe to eat. Small amounts persist after cooking and have no apparent effect on health.
Appreciation of manioc's diversity is critical to understanding its spatial spread. Cultivation of this plant in South America for more than five millennia has resulted in at least 2,000 named varieties or cultivars and about 6,800 landraces which are local variations, often not named, that are not improved by a formal breeding program (Bonierebale et al., 1997:12). Although farmers use cuttings, not seed, in reproducing this crop, clonal diversification has nevertheless occurred when manioc plants produce flowers. Cross-pollination spontaneously can occur between two cultivars or between a cultivar and a wild species of Manihot. If the farmer perceived some benefit in the resultant variation, he propagated it which assured its survival and diffusion. Since the plant cannot disperse on its own, human agency has always accounted for its presence elsewhere. The folk selection process of manioc began far back in prehistory. One development outside the tropical zone was the emergence of clones that mature their roots in only six to ten months.
Cold weather affects this tropically derived species at several thresholds. When the lemperature dips below 15[grados]C, growth stops. If those lows continue for several days running, the plant loses its leaves and enters a dormant phase (Normanha and Pereira, 1967). The apical parts of the plant die when temperatures drop to between 8[grados] and 10[grados] C and air temperature of 5[grados] C normally kills the whole plant. None of these temperature thresholds, however, prevents manioc cultivation. Since cold weather comes mainly after the plant has been harvested, it is not a major hindrance. Many mid-latitude areas have seasonal monthly and daily temperatures that satisfy the plant's physiological requirements for successful root production.
Most growers in the southern reaches of manioc distribution treat this perennial plant as an annual. As the cold season approaches in April of May, they dig up the whole plant, hack off the usable roots, and cut up pieces of the woody stem to be used as planting material for the next planting season. Unlike sweet potato of the potato, the tuberous roots of manioc only store energy and have no reproductive function. In areas where a strong freeze is expected, farmers bury of at least cover these lignified cuttings (called estaca in Spanish and mandiva in Portuguese). Planting of the propagule occurs in October of earlier. The storage roots start enlarging three months later and in March they may be dug up as food. Roots harvested young, though relatively small, have a better flavor and less fiber than older roots. However, when manioc is to be industrialized, overwintering is the preferred practice. In spring the above-ground stem refoliates and growth quickly resumes to increase the volume and weight through all or most of the second growing season. Roots harvested afler 18 to 24 months in the ground are large and thus add to the labor efficiency of a commercial operation.
Cultivation and Processhzg
In its southern extent manioc is grown at various scales and for several different uses. On small farms manioc is usually planted with several other crops in small plots with minimal investment in agrochemicals or fertilizers. The fact that manioc can yield satisfactorily without these adjuncts is one of this plant's great advantages. Several weedings, however, can not be ignored. If to be eaten fresh, roots are dug up as needed over a two-month period. In both southern Brazil and northern Argentina, freshly harvested manioc is boiled and eaten throughout the day as a bread substitute or added to stews. Part of the harvest may be sold if a market exists to buy it. At least 30 percent of the harvest in the reach zone is fed to pigs, oxen, dairy cows and chickens. Manioc fields of more than one hectare yield quantities intended for processing into more preservable products.
In Rio Grande do Sul, both bitter and sweet varieties are grown; the former are used for culinary purposes or fodder; the latter for processing. Harvested roots in the sweet group are not commercialized, whereas bitter varieties are used for flour (farinha) manufacture. Although called farinha, it is more like a meal than the powdery texture of wheat flour. Processing has taken place in small milling installations called atafonas which use variations of the wooden screw press. This piece of European technology was first introduced from Portugal where it had been used to press oil from olives and must from grapes (Fernandes, 1964). The original animal power was later replaced by water, steam or gasoline engines which made larger presses possible. Harvested roots are washed, peeled, and then pulped. Pressing removes most liquid which is discarded. The pulp is then placed in pots to be dried and toasted over a tire to volatize residual poison and add palatability. Brazilians have long preferred their manioc in this form. Farinha is an indispensable part of feijoada, the emblematic dish of meat, rice and black beans prepared more than 50 million times a day around the country. For the flavorful variant called farofa, oil, salt, and sometimes egg and onion are added to the manioc flour and toasted shortly before serving.
Another edible manioc product is starch. In the South of Brazil, the starch when dried is called polvilho. A preferred variant is sour starch, called polvilho azedo, made by placing the roots in water so they undergo lactic fermentation. That chemical reaction, combined with sun-drying the pulp, gives the starch the capacity to trap air and expand. This product is much used in making baked goods, especially pao de queijo. In Northern Argentina, manioc starch is rarely fermented and much of it is made at an industrial scale to supply the food industry and manufacturers who use it in products like glue and laundry starch. Manioc has also been grown as a source of industrial alcohol.
Manioc in its Southern Reach
The meridional extent of manioc involves borders, that is, a district lying along the margins and the boundaries which refer to lines of demarcation. Manioc's "reach zone" is the penumbral projeetion of the crop in eastern South America between latitudes 28[grados] and 31[grados] 48' S. It forms manioc's most poleward distribution in the world. Two sub-regions comprise the southern reach: a) the transitional area where that crop has a measure of economic significance, primarily as a field crop and is integrated into food habits; and b) the fringe area where the crop is mainly a garden crop and marginal in the agroecosystem or diet (Figure 2). The southern edge of the transitional area defines the normative boundary of manioc cultivation. More than 90 percent of the manioc cultivated and harvested in the reach zone comes from the transitional arca (IBGE, 1943; 1996; Argentina, 1939; 1968; Corrientes, 1969). Considerable fluctuation in manioc production in Southern Brazil and Argentina in the twentieth century has been mostly a response to the rise or decline in industrial uses, not changes in domestic consumption.
[FIGURA 2 OMITIR]
Though vast in extent, the fringe area in Brazil, Uruguay and Argentina has in any one year no more than 3,000 ha of land in fields or gardens devoted to manioc. Agronomists consider this space to be distinctly marginal for growin manioc and discourage it as an element of land use there (Rio Grande do Sul, 1975: 127). With the exception of Santa Vitoria do Palmar and Jaguarao, the southernmost tier of municipios forms Brazil's manioc fringe. It extends across the border into northwestern Uruguay south to about Tacuarembo and Salto. The Argentine fringe area includes southern Corrientes and the northern parts of Entre Rios, Santa Fe, Santiago del Estero, Salta and Jujuy Provinces. Manioc cultivation south of the normative boundary is diffuse and casual. Since manioc is not a crop on which they depend, growers there can afford to make individual decisions about growing it of not. Failure due to an early freeze of to using inappropriate cultivars can strike manioc from next year's planting list. Winter desiccation of unprotected planting material can be the excuse for not growing it again. The simple desire to plant a smaller garden than before can remove manioc from the local landscape. These decisions do not respond to an economic imperative, but nevertheless can set the outer boundary of its cultivation.
Here and with different crops in other places a kind of folk wisdom emerges at crop borders about what is worthwhile to grow in given places that comes from the planting experiences of generations of farmers and gardeners. A decision to plant a particular crop rests on familiarity as much as utility. When a crop is mapped, placement of the outer limit of its cultivation will vary depending on how that boundary is conceptualized: relative importance vs. non-importance as one criterion or sheer presence vs. absence as another. Since individual decisions in the fringe area create idiosyncratic and ephemeral distribution patterns, the absence/presence differential must be rejected as having no substantive geographical significance.
Wherever they fall, boundaries of cultivation for any crop are not coextensive with limits of its utilization. Manioc is shipped, marketed and eaten beyond the outer confines of its production. In cities such as Salto (Uruguay); Salta (Argentina); Uruguaiana (RGS) and Rio Grande (RGS), fresh manioc root arrives as a seasonal vegetable beginning in March. Farther beyond its zone of cultivation, the per capita demand for manioc is both low and specialized.
Several environmental factors correlate with the southern reach of manioc cultivation. Rainfall is not among them, although manioc is often viewed as a plant of high moisture requirements. Certainly areas of high precipitation often have high manioc production; most of Misiones, the leading manioc-producing province in Argentina, has more than 1500 mm of rainfall. The sharp rainfall gradient westward from the Paraguay-Parana riverline to the Andean front also corresponds to a decrease in production: Corrientes receives 1268 mm; Roque Saenz Pena 990 mm; and Salta 671 mm. However, rainfall must be discounted as determinative in manioc boundaries. Farmers can choose cultivars adapted to low moisture requirements or direct irrigation water to the household garden. Occasional droughts in normally humid Northeast Argentina place stress on manioc plants by decreasing photosynthesis and reducing root production. However, these weather occurrences are normally too episodic to make a farmer of gardener change his or her behavior about growing this crop.
Most of the reach zone but also large areas beyond it to the southeast is hot in summer and cool of mild in winter with rainfall distributed throughout the year. However, within this region, summarized as Cfa ("humid subtropical") in the Koeppen classification, important differences characterize the latitudinal spread of temperatures between April and September (Mota Agendes, 1986; Rudloff, 1981 ; Werenstedt, 1972), July, the coldest month almost everywhere, is a key indicator of the winter differences. In eastern Rio Grande do Sul, the winter cold intensifies 3[grados]C in 450 km: Porto Alegre has a July average of 14.3[grados] C, Pelotas 11.9[grados] C and, beyond the manioc area, Santa Vitoria do Palmar, 11.3[grados] C. (5) In the Parana Valley, the July average decreases 2.8[grados]C in 450 km: 15.8[grados] C at Posadas, and 15.7[grados] C at Corrientes in the transitional area to 14[grados] C at Goya and 13[grados]C at Esquina, both in the fringe zone. Just beyond the absolute limit of the crop is Santa Fe with 12.3[grados] C and well beyond it is Rosario at 10.2[grados] C. Farther west, Tucuman and Santiago del Estero both have a July average of 12.8[grados] C, but both lie outside the fringe zone.
Low seasonal temperatures complicate manioc cultivation (Westphalen and Maluf, 1981). Yet limitations set by winter cold is a vast oversimplification in understanding manioc distribution. If rapidly-maturing cultivars are used, manioc cultivation can overcome thermal control. By the onset of low temperatures in April, usable roots can be harvested. Tomato, capsicum pepper, maize and phaseolus bean bear an agronomic analogy to manioc. All four are New World crops of tropical origin that expanded into middle latitudes up to ca. 47[grados] latitude when plant breeding turned them into short-cycle annuals. Genetic change of various kinds --genetic drift, artificial selection, and plant breeding-- transformed these crops to be able to complete their reproductive processes within the frost-free period of the growing season. Manioc variation includes cultivars which develop usable roots in a growing season of ca. 180 days or fewer during which the daily mean temperature does not fall below 15[grados] C.
However, these minimum requirements of temperature and growing season do not necessarily correspond to actual manioc boundaries. The geographic reach of manioc reflects instead a daylength imperative. Experimental studies conducted from Cariada (Lowe, Mahon and Hunt, 1976) to Australia (Keating, Wilson and Evenson, 1985) and Brazil (Carvalho and Ezeta, 1983) have shown that photoperiod is an important factor in manioc root development. Bolhuis (1966) found that manioc plants yielded a heavier and more voluminous root harvest when photoperiods were 10 and 12 hours long as compared to 14 and 16 hours long. Research by Mogilner, Orioli and Bletter (1967) and Portugues Arias and Mogilner (1967) corroborated observations that daylight periods of more than 12 hours inhibit root bulking. Cock (1978) clarified the relationship of light and growth by demonstrating that long daylight during the first three months after planting substantially reduce root size.
The accumulated experimental data points strongly to understanding the main hindrance to manioc in the mid-latitudes. The period of daylight lengthens until the summer solstice which, in the Southern Hemisphere, is reached near the end of the year. At that time, leaf and stein development of the manioc plant has provided the photosynthetic basis to activate growth of underground storage organs. However, if the days are long, stems continue to grow at the expense of the storage roots. Daylength of 14 hours may be a critical threshold in establishing the limit of a generally accepted satisfactory yield. On December 21, that daylength occurs at 29[grados] S; on that same day, latitude 17[grados] S has 13 hours of daylight and 41[grados] S has 15 hours. Roots harvested in the fringe zone are characteristically one half to one third the size of those produced in the tropical parts of Brazil. Ironically, the long days and high temperatures produce a lot of above-ground biomass which gives a false appearance of high yields to come. Definition of an acceptable harvest varies with the individual grower. This uneven reaction explains why the absolute boundary is not a solid phalanx, but a series of isolated manioc plantings here and there. Meager root harvest might be acceptable if the plant had compensatory value to growers in the fringe area. Manioc does not add nitrogen to the soil and its woody stems are not important as a fuel.
In the reach zone of southern South America, long periods of daylight can hinder manioc growth as much as cold weather which makes it difficult to separate their effects on manioc distribution. Weather events are commonly perceived as decisive in exercising control on production and survival (Westphalen and Maluf, 1981). An unexpected brutal freeze in early spring or late autumn can foreclose a harvest. The climatic effect is most apparent when long-cycle cultivars are planted in high latitudes and when they must cope, often unsuccessfully, with at least two months with average temperature below 15[grados] C.
Although soils do not set the southern limits of manioc, they influence its regional distribution. Soils well-drained if poor in nutrients are preferred. Manioc grows especially well in a rich medium, but is usually relegated to nutrient-poor sites. Commercially-oriented crops merit the more fertile substrates. Permanently wet soils, which curtail root development and encourage rot, offer the major pedological constraint on manioc cultivation. For that reason, very little manioc is found in the esteros of central Corrientes, marshy floodplain of the lower Parana Valley, poorly-drained sections of the Chaco and areas of clay soils. In low-lying ground, manioc can be grown if the water has drained off in time for planting or if raised fields are made for it. In either case, however, roots must be harvested before high soil humidity seeps in to rot the roots during the cooler months of the year. Floods, big and small, have destroyed standing mandiocales, as when huge tracts of territory in the Argentine Northeast were submerged in the early 1980s and late 1990s (Valenzuela de Mari, 2001). Insects and pathogens also can have a negative impact on manioc cultivation, especially since this plant rarely receives pesticides. Stemborer (Chilomina clarkei), an insect, and bacterial blight, a fungus, are sometimes troublesome in the reach zone. However, neither phytopathology nor pedology sets the lalitudinal manioc boundaries at a small scale.
Ultimately, manioc distribution is an expression of agronomic choice. A farmer's or gardener's decision, not a biophysical limit, accounts for its presence. As a human food, livestock feed or industrial product, manioc is useful, but nothing about this plant in the reach zone makes it necessary or irreplaceable. It is a choice conditioned by history, diet and land use (Schmidt, 1956). Brazil's particularly strong association with manioc has its metaphoric roots in a pre-contact horticultural tradition that virtually all the early European explorers and travelers mentioned. Like maize in Mexico or the potato in Peru, manioc has held and still holds an iconic role in Brazilian culture as an ancient and dependable staff of life. Recently analyzed genetic evidence of wild species of Manihot points to a domestication in Mato Grosso (Olsen and Schaal, 1999). Allem (2001) acknowledges that the wild ancestors of manioc carne from the wet-and-dry tropics, but offers a different hypothesis in favor of an Amazonian domestication. In either scenario, manioc deployed southward into the mid-latitudes only much later. Between 500 and 1000 C.E., migrating Tupi-Guarani people brought this and other plants with them as part of their subsistence base (Figure 3). Knowledge and use of manioc spread to the Caingang in the Ge language group which turned them from hunting and gathering to swidden agriculture. Use to make alcohol was plausibly an important motive for its early spread. Two traditional uses for manioc known in northern Brazil, making a sauce and consuming the boiled leaves, were apparently not transferred to the South (Lancaster et al., 1981; Normanha, 1982). Manioc had more competition from maize in southern Brazil than in the North where the former plant has been and still is several times more important as a caloric source than the latter.
Europeans carne in the sixteenth century with livestock which the Guarani rapidly embraced (Service, 1951:248-9). The high productivity of manioc enabled the Guarani to feed these roots to both themselves and their newly acquired domestic animals. In the early seventeenth century, manioc cultivation intensified when Jesuit missionaries enticed previously dispersed Guarani people into 30 theocratically-based settlement clusters. Inhabitants of these mission towns spread over eastern Paraguay, northeastern Argentina, western Rio Grande do Sul, and northern Uruguay grew manioc as a food staple. Four towns in the Uruguay River drainage, Santo Tome, y Sao Borja, La Cruz and Yapeyu, were in the fringe zone where livestock grazing was the main activity and where conditions for growing the plant were less than ideal. Nevertheless, manioc and maize prevailed as the dietary foundation of the Guarani missions in spite of the adoption of many other aspects of European civilization (Cardiel, 1989:64). In 1767, the colonial governments expelled the Jesuits and the Indians in them gradually dispersed, but in that century and a half of agronomic attention, manioc surely underwent selective pressures toward survival in marginal environments.
In Brazil, knowledge of manioc acquired originally from indigenous people of several tribes was integrated into the agricultural inventory and dietary habits of groups who came there from beyond. Commerce in manioc products took on new importance when coastal plantations in southern Brazil produced farinha as the main onboard provision on transatlantic slave ships. Manioc sustained the European settlers who went to southern Brazil early in the nineteenth century (Hormeyer, 1986). Crops brought with them from the old countries did not adapt well to either the subtropical climate of to the swidden mode of farming that made animal-pulled plows impractical. Justas their cohorts in North America adopted maize as their staple, immigrants to rural southern Brazil turned to manioc. Though not balanced nutritionally, manioc served as a basic energy source for people doing hard labor. When converted into flour, 100 grams yield 354 calories. The Portuguese names given to most manioc cultivars in Brazil suggests the crop's cultural integration. Dependence on manioc as a feature of Brazilian diet was also apparent where the crop could not be produced. In the eighteenth century, shiploads of manioc flour were sent from Santos to its outpost of Colonia do Sacramento (now: Colonia del Sacramento) on the Rio de la Plata where its cultivation was considered impossible (Porto, 1954:400).
In Uruguay, by contrast, manioc has a shallow history. All five tribal groups, of which the Charrua were the most numerous and widespread, followed a nomadic hunting tradition. The European settlers who displaced them practiced ranching as their primary land use. The farming that emerged focused mainly on wheat-growing. Brazilian influence led Uruguayans to import manioc flour, which they called farina to distinguish it from harina which is wheat flour. Two campaigns of manioc cultivation in Uruguay, one in the 1870s and the other in the 1940s, were not sustained over the long term (Berro, 1914:150: Christophersen, 1950:50; Paiva, 1952). Freezing temperatures reportedly reduced yields, which may have been avoided if short-cycle cultivars bad been planted. Today manioc is of no commercial significance as a crop in Uruguay. A few scattered plantings occur southward from the Brazilian border, but its production is so modest that it does not enter into the agricultural census.
In Argentina, manioc is an important crop and food in Misiones, Formosa, Chaco and northern Corrientes. This region combines the best environment in the country for growing the plant and the strongest Guarani historical influence. The Guarani connection is apparent in the names for many older manioc cultivars (Bravo, 1950:5). Several much-loved foods in Argentina have Guarani origins. Chipa is concocted with homemade manioc starch to which oil, milk, egg, salt and cheese are added and then baked in a primitive oven. Manioc starch is also used to make mbeyu, a popular kind of pancake. Popi is manioc peeled and dried in the sun. Fresh boiled manioc is a bread substitute of a basic vegetable ingredient in soups and stews. Unlike Brazil, most manioc foods in Argentina are prepared from sweet cultivars. Historically, bitter varieties were also grown (Vazquez de Espinosa, 1942:688; Hernandez, 1888:69-70).
Manioc is a cultural identity marker to people in the Guarani tradition when they move to the big urban centers of the Pampa. Chipa is the most emblematic dish, even though it is now moving toward popular acceptance as a snack food somewhat in the same way as tacos have in North America. In metropolitan Buenos Aires and in Rosario, migrants from the Northeast and Paraguay are the ones who buy manioc brought by wholesalers from the north and sold in neighborhood markets (Stroppa, 1990).
The cultural core of the Guarani tradition is Paraguay, where the Indian language continues to dominate the mestizo peasantry. Manioc is central as a crop as a food. Paraguay has the highest per capita production (700 kg/year) and consumption (110 kg/year) of manioc in the entire Western Hemisphere (Carter, 1986). The great majority of farmers in eastern Paraguay grow it as part of an intercropping scheme with maize, beans and peanuts. Manioc is the dietary staple of the peasant household. It is also an important livestock feed for pigs and chickens. If nearby cities are easily accessible, harvested roots can be marketed as a cash crop. Paraguay is an important source of landrace diversity. Whereas Argentina has an estimated 24 such varieties, Paraguay has 192 (Bonierbale, 1997:12). Some manioc landraces that had their origin in Paraguay spread successfully to Argentina. Today, however, most cultivars grown in Argentina come from scientific plant-breeding programs.
Northern Argentina includes many people who have no Guarani roots but who nevertheless are influenced by those who do. Especially in Misiones, Europeans came as agricultural settlers as late as the 1950s. Ethnic villages and towns and their surrounding fields carved out of the forest still have a pioneer aspect (Eidt, 1971). As in southern Brazil, manioc fit into the colono agroccosystem as a dependable source of food and livestock feed. This crop could be counted on to produce as settlers cleared the land and made the difficult transition to a viable household economy. The latosolic "tierra colorada" soils that cover more than 80 percent of Misiones produce good manioc harvests. The German-Argentines in Eldorado and Montecarlo became as enthusiastic manioc growers as were the German-Brazilians in Gravatai and Estrela. Some farmers in both places later expanded production to an industrial scale. In Misiones, small entrepreneurs established starch factories and that province is where most commercial manioc processing in Argentina is still centered. Rio Grande do Sul once had about 130 industrial processing installations for farinha and starch. In Brazil, however, manioc processing has been very diffusely spread over the country, for the crop can be grown more cheaply in Minas Gerais and the Northeast than in the South.
Competing Land Use
Manioc as a land use is displaced progressively southward not only by biophysical limitations. The grasslands that have covered most of southern Rio Grande do Sul, northern Uruguay and northeast Argentina have long been grazed by livestock raised on holdings mostly in excess of 1000 ha. Less than five percent of the land is in cultivation; most of that is held by tenant farmers who grow unirrigated wheat or, in more recent decades, irrigated rice. Estancias also maintain maize, beans and manioc plots to complement their dominant nutritional focus on meat. If peasant farmers had at some point turned the grassland into a densely settled agricultural area, manioc would have had a larger place in the domestic economy.
Reflections on Manioc Boundaries
Boundaries and Perception
Defining a crop's boundary requires consideration of scale and intent. At a small scale, a cartographic line conveys a high level of generalization; if that line is transferred to a meso-scale it would no longer be accurate. Cock's (1985:16) strong assertion that manioc is "... never grown as a crop further from the equator than 30[grados] N or 30[grados] S" is a reasonable generalization on a map of the world. Other manioc scientists have used this as their shorthand for this crop's distribution (Balagapolan, 1988:7; Bonierbale, et al., 1997: 1). Pimental's (1948) remark that manioc is 'cultivated everywhere in Brazil' is a reasonably useful statement. However, the southeastern corner of Rio Grande do Sul vitiates that assertion. Monolithic statements about latitude or national territory are not meant for scrutiny. But when applied to a larger scale map, the resolution level changes and greater precision has to take over.
Aside from scale per se, the statistical mapping unit chosen also determines boundary placement. On Carter's (1985:22) map of manioc in South America, one dot represented 1000 ha under cultivation. A cartographic line drawn from that decision falls about 200 km farther north than the earlier defined normative limit. Pfeifer (1967) provided another southern limit of manioc in Rio Grande do Sul without, however, explaining his criteria.
Boundaries through Time
Aboriginal migrations extended manioc cultivation southward and westward. Between A.D.1300 and 1400, Guarani agriculturalists descended the parallel-flowing Uruguay and Parana Rivers to their deltaic confluence on the Rio de la Plata (Figure 3). To create their own subsistence base in a zone of non-agricultural people, the Guarani had to take planting material with them. Precisely how far to the south manioc was part of that pre-Conquest agricultural advance remains a matter of conjecture. Some authors eliminate manioc as a historic crop in the Guarani enclave in the Parana Delta for a priori climatic reasons (Acosta y Lata, 1979:7; Ibarra Grasso, 1967:317). Soils there were also wet. Archaeology does not corroborate its pre-Conquest presence there, nor is there unequivocal documentary evidence of it that far south in the early historic period. Two sixteenth-century explorers mentioned manioc as a crop and as a food provision only when they reached northern Corrientes (Schmidel, 1903; Nunez Cabeza de Vaca, 1984). This pattern suggests that the normative boundary of manioc between the two rivers was substantially the same 400 years ago as it is today.
[FIGURA 3 OMITIR]
A Guarani connection also accounts for the presence of manioc between the Parana/Paraguay Rivers and the Andean front south of 17[grados] S (Metraux, 1928:66; Storni, 1944). Ancestors of the Guarani-speaking Chiriguano carried sweet manioc in their fifteenth-century migration to present-day eastern Bolivia. Although primarily maize farmers, they also grew and used sweet manioc which distinguished them from their non-Guarani neighbors. Far to the north extensive pre-Columbian earthworks built in the Llanos de Mojos area of northeastern Bolivia provided an ingeniously managed micro-environment for growing rootcrops in flood-prone swampy terrain (Denevan, 1967). Whether manioc had spread southward from there remains unclear. Rosen (I 957) speculated that ridged fields of apparent pre-Columbian origin in the Lerma valley around the city of Salta (1226 m above sea level) may have been designed for manioc cultivation. However, no clue in the historic of present farming of diet of this area supports such an idea. Yet, farther south, experiments have demonstrated the feasibility of manioc production near Tucuman (27[grados]S) (Folquer, 1982).
For northwestern Argentina, Cushner (1980:89) recorded manioc among the crops grown in the seventeenth century by African slaves on the Jesuit estates near Cordoba (31[grados] 24' S). Manioc's presence there may have reflected its slave association that started when Africans were fed hardtack and farinha on their long transatlantic journey. Once in Brazil, slaves by preference kept manioc as their major food. The civil authorities favored slave-grown mandioca as an efficient energy source. Moreover, work regime on estates required a productive staple that did not need a lot of cultivational attention. In 1688, King Peter I institutionalized that connection when he required each slave to plant of have planted for them 500 manioc stems. Slaves taken beyond Brazil to the Rio de la Plata were able to grow the plant only when they were transferred to estates farther north in Argentina. However manioc distribution is not necessarily a legacy of the provision ground for the African slave. The nineteenth-century record of manioc in northern Salta Province was more likely a result of the earlier Chiriguano diffusion (Mantegazza, 1949:320).
Manioc in Rio Grande do Sul has had a relatively stable distribution pattern over the past two centuries. Azara (1809:146), whose observations were in the early eighteenth century, placed the normative limit of its cultivation close to what it is today, i.e. latitude 29[grados] S. Auguste de St. Hilaire (1946:60), traveling northward on the Brazilian side of the Uruguay Valley in the 1840s, first noticed its appearance as a crop between Sao Borja and Sao Nicolau. Near the Atlantic side of Rio Grande do Sul, Dreys (1961:80) found manioc, sugar cane, coffee and orange trees growing at the latitude of Porto Alegre (30[grados] 03' S). At Camaqua (30[grados] 50' S), coffee had dropped out and the other plants had become uncommon. At the city of Rio Grande (32[grados] 45' S), all four plants had disappeared from the surrounding agricultural landscape. In the same decade, Saint-Hilaire (1946:53) traveling that road observed manioc plantings as far south as Porto Alegre.
Change in manioc cultivation corroborate the important role of photoperiod when two sets of manioc statistics, one for 1940 and the other for 1990, are compared for southern Rio Grande do Sul (IBGE, 1943; 19937. Manioc plantings in the southern tier of municipios along the Uruguayan border went from nothing to 210 hectares in that half-century period. If one, however, takes the 11 municipios located all or mostly south of 31[grados] 30' S latitude, no manioc plantings are recorded for either date. Climate differences are not persuasive in explaining this latitudinal difference.
Manioc's past or present distributions cannot be used to make useful predictions about the future. Biotechnology could radically change the constitution and geography of this plant within a short time period. When gene structures are understood, biochemical pathways modified and transgenetic technology employed, development of new manioc cultivars will greatly increase (Puonti-Kaerlas, 2001). Breeding of clones that do not respond to differences in photoperiod ("day neutral"), especially if combined with cold resistance and helped by global warming, could permit manioc dispersal into the middle latitudes of all continents. The potato (Solanum tuberosum) is a major historic example of genetic change from a short-day plant of 12 hours of light in its homeland in the Peruvian Andes into one tolerant of days with as much as 20 hours of light in northern Europe. Two centuries of selection for long summer days were required before the potato became a European field crop in the mid-eighteenth century. Advances in preserving the fresh root could also dramatically change trade in manioc. Paraffin coating of the roots, a process which delays deterioration for about two weeks, has made it economically viable to ship fresh manioc from Costa Rica to the United States. Its future cultivation in places where it has not been a crop is likely to come from the plant's potential as livestock feed and as an alternative source of industrial starch than for its use as human food.
Manioc Boundaries Elsewhere
Three other manioc borderlands in the world offer comparative perspectives with southern South America of its relative acceptance or sheer failure. In North America, both east and west, sustained cultivation of this plant has remained far south of its potential limit. Its cultural-historical absence on the Florida peninsula is especially puzzling. No archaeological evidence yet confirms that manioc had passed to Florida from the Caribbean where Columbus discovered its use everywhere he went. Nor did Florida Indians grow the plant after Spaniards arrived from the Caribbean presumably with manioc cuttings on board. Spaniards had earlier learned to make the flatbread casabe on Hispaniola.
The Seminole, who came into the Florida peninsula from the north in the eighteenth century, did not adopt manioc. However well adapted manioc was to growing in the tropical wet and dry climate of South Florida, the Seminole instead made starch flora wild-growing cycads (Zamia). In the nineteenth century, Florida entrepreneurs made industrial starch from manioc, but when com starch became cheaper, these plantings disappeared. Some manioc was sporadically grown as far north as the Gulf coastal plain of Mississippi as a livestock feed (Tracy, 1903). In the early twentieth century Florida extension agents promoted manioc for home gardens but with minimal success. A commercial production of the fresh root later emerged in Dade County to supply the population of Caribbean origin living in South Florida. Except for tapioca, manioc as a food still had strong ethnic associations in the United States at the turn of the twentieth century.
West of 95[grados] W in Mexico, manioc also failed to get established in places where it could have grown. Guacamote, as the plant is called in Mexico, has traditionally been a strong part of the agricultural inventory only south of 20[grados] N. In Sauer's (1969:127) view, its failure to spread northward into other warm parts of Mexico and the American Southwest is based on a deep-seated preference for seed agriculture that blocked serious acceptance of vegetatively reproduced crops.
Subtropical Africa offers another comparative perspective on manioc distribution. Between 20 and 30[grados] S. latitude, only Mozambique has important manioc production (Romanoff and Lynam, 1992:31). The Portuguese, who occupied Mozambique beginning in 1507 and governed most of it for more than three centuries, introduced manioc cuttings from Brazil. By showing Africans how to process the root to make it sale to eat, manioc became an indispensable part of subsistence farming. Today this one plant supplies an astonishing 42 percent of Mozambique's total calorie intake (CIAT, 1993). By contrast, rural folk in similar latitudes in southern Zimbabwe, Botswana, Namibia and South Africa have long depended on maize as their staple food and in much of that area manioc is unknown. At least some of the sharp difference in production and consumption of staples in southern Africa can be attributed to divergent colonial influences. British colonialists in southern Africa denigrated manioc as an inferior food, whereas the Portuguese valued it as a crop and imparted to Africans in Mozambique the skills to deal with manioc's variable toxicity and perishability. Behind the failure of manioc to successfully diffuse into areas where its cultivation might be expected may lie stories inscribed in the folk memory and oral tradition of individual tragedies based on ignorance about its baneful character.
Another example of manioc failure lies at on the islands and mainland at the margins of the European continent. There. long-day length best explains why manioc did not get a foothold in the mild climates of the Iberian realm. Easily transported manioc stein cuttings were surely introduced, perhaps repeatedly, to the Andalusian coast (36[grados] 44' Nat Malaga), the Canary Islands (28[grados] 07' Nat Las Palmas) and Madeira (32[grados] 41' Nat Funchal). However, none of these places has a historical record of successful cultivation of this plant. Madeira is a particularly interesting failure in view of the many reasons why manioc might have found a place there. It had numerous early sea connections with Brazil with the arrival of people who knew how to process it. The island had an intermediary role in the African slave trade for which it was a shipboard provision. Madeira has a mild climate near the coast with no month falling below 16[grados] C at Funchal. The island has had a proven productivity of other tropical crops including sugar cane, banana and sweet potato (Ipomoea). A dense population would have benefited from growing such an efficient source of carbohydrates as manioc. Most likely, manioc was planted in Madeira over a period of years, but without a satisfactory harvest of roots until, finally, those attempts at cultivation were abandoned and the crop was forgotten.
Climate has wrongly received the most attention as the key controlling factor in manioc's generally stable normative boundary. Much of that assumption lies in this plant's origin in the low latitudes and its optimum growth where the mean annual temperature exceeds 20[grados] C. Manioc suggests tropicality in a way that few other root crops do. Nevertheless, thermal thresholds do not set the present poleward boundaries of its cultivation. If that were the main consideration, short-cycle manioc could grow more than 500 kilometers beyond the present normative boundary. Instead, long days during the growing season inhibit root enlargement and the meager yields make it futile to cultivate much beyond its present limits on the basis of the cultivars presently known.
In the end, however, it is human decisions, not biophysical determinants, that account for the presence of manioc cultivation in subtropical South America. Two cultures with historically derived affinities for manioc have carried the plant into extra-tropical latitudes up to 31[grados] S. Both the Guarani and Brazilian traditions have valued manioc as food for man and beast. Although now syncretized with European elements, Guarani culture is a widely-diffused transnational force of indigenous origin which goes back more than a millennium in South American culture history. Brazilian culture is an amalgamation of diverse peoples into a national culture that crystallized about three centuries ago. It has asserted itself in almost every corner of Brazil that from time to time has spilled over into adjoining countries. Rural people in both those traditions know how to grow manioc and are experts in turning the raw root into articles of consumption in accord with their own culinary emphasis. It is not simply that cultures have affinities for familiar foods and reject those with which they have no experience. Though manioc is useful and easy to grow, processing is the key to its dietary integration. That is the main reason why in subtropical North America and most of southern Africa, this crop is not important in agroecosystems or diets. Phasing out of manioc cultivation in the South American fringe area has as much to do with competing land uses as with any other factor.
The study of crop borders and boundaries requires two kinds of convergence: physical with culture and time with space. Understanding their larger meaning involves bringing together, on one hand, biophysical processes and physiological tolerance limits and on the other, a range of human factors. In addition, the spatial contexts of agriculture, migration and settlement benefit from juxtaposing them in the past with the present. Those twin perspectives open the realization that agricultural boundaries are not a straightforward causal relationship with just one kind of controlling factor. The crop plant is a classic manifestation of a nature/culture gestalt whose possibilities reflect human modifications as much as physiological tolerance limits. As such, agricultural boundaries are not immutable. Migration of people change crop distributions, but behind that are genetic changes in crop plants themselves that permit altering borders and boundaries.
* Acknowledgements: Primary support for the field research that went into this paper came from a 1992-93 Fulbright award under the American Republics Research Program for Brazil. Uruguay and Argentina as well as a travel grant from the Research Program of the Association of American Geographers. Mary Scott Killgore Gade, recipient of a Fulbright award for study and research in Brazil in 1963-64, has provided thoughtful commentary on this manuscript and made the maps for it.
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Daniel W. Gade, Professor Emeritus of Geography University of Vermont. Telephone: 802-862-4751. Mailing address: 30 Harrington Terrace, Burlington, Vermont 05401 USA. E-mail: email@example.com
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