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fechar este livroRoots and Tubers for the 21st Century - Trends, Projections, and Policy Options. 2020 Vision for Food, Agriculture, and the Environment. Discussion Paper 31 (IFPRI, 2000, 72 p.)
Ver o documento(introduction...)
Ver o documentoForeword
Ver o documentoAcknowledgments
Ver o documento1. Introduction
Ver o documento2. Trends in the Use of Roots and Tubers
Ver o documento3. Trends in the Supply of Roots and Tubers
Ver o documento4. Baseline Projections of Production and Use
Ver o documento5. High Demand and Production Growth Scenario
Ver o documento6. Roots, Tubers, and the Environment
Ver o documento7. Conclusions and Recommendations
Ver o documentoAppendix: Supplementary Tables
Ver o documentoReferences

6. Roots, Tubers, and the Environment

Prospects for continued increases in supply and demand of R&T in developing countries have raised concerns about the impact of their output and use on the environment (see for example Bardhan Roy et al. 1999; Crissman, Antle, and Capalbo 1998; Goletti, Rich, and Wheatley 1999; Howeler 1996). Cultivation of some R&T can help slow soil erosion (see, for example, Orno 1991) and new technologies may systematically increase the level of genetic diversity under cultivation (Upadhya et al. 1995). Technological progress, institutional innovations, and changes in policy can and should be geared toward sustaining the resource base while increasing supply and demand.

This chapter briefly examines the environmental problems and potential associated with R&T. Not intended as an exhaustive review of the literature, it identifies instead a cross-section of issues, technologies under development, and associated policies that can help ensure that increased R&T production and use are environmentally sustainable. It should be noted that many of these problems or potential opportunities are by no means exclusive to R&T.


Improper use of pesticides is a major environmental concern in potato cultivation. Pesticide use is far less frequent and less potent with the other R&T. The vast majority of resource-poor farmers who cultivate cassava, sweetpotato, and yam have limited access to these products or cannot justify their use given other demands on their limited cash resources.

The most widespread and intensive use of pesticides in developing countries is for controlling late blight potato disease caused by phytophora infestans. Farmers in some countries spray their potato fields up to 15 times during a single growing season of 4 to 6 months in order to combat this disease (Hijmans, Forbes, and Walker 1999). Pesticide sales to potato producers in developing countries exceeded an estimated US$150 million in 1991 (Oerke et al. 1995, 459). Pesticides can also constitute a formidable health risk to farm families and farm workers engaged in potato production (Antle et al. 1998).

With the emergence of new, more virulent strains of phytophora, the fear now is that late blight and other pests and diseases will develop resistance to the current array of pesticides. Consequently, even heavier applications of chemicals may end up providing even less protection against plant damage, resulting in greater loss of food (Erselius et al. 1999) and potentially greater harm to human life (see, for example, Cole et al. 1999).16

16 The estimated value of the loss of production in developing countries in 1997 due to late blight was US$2.5 billion (CIP 1998, 16-17).

Pesticides are also used against other potato diseases and pests, such as insects. In spite of the extremely high cost and potentially harmful consequences of many of these chemicals, users continue to apply them because the risk and value of crop losses are so high.

Concerns with environmental and health impacts, combined with a growing appreciation of the damage different pests and pathogens can do to R&T, have led to the development and diffusion of an array of alternative technologies. These include disease-resistant varieties (Landeo et al. 1997), pheromone traps (Alvarez et al. 1996), targeted use of natural predators, and integrated crop management techniques that combine reduced applications of pesticides with improved cultivars and natural barriers to pest infestation. Increased production and use of potatoes may well boost the total cost of pest damage and the potential for adverse environmental effects from improper use of pesticides, but it will also increase the rewards associated with more environmentally friendly agricultural and postharvest practices.

Moreover, as Lee and Espinoza (1998) note in their case study of Colombia and Ecuador, changes in government policy, including greater market determination of exchange rates, liberalized trading regimes, elimination of government-administered pricing systems for imports such as pesticides, decrease in agricultural credit subsidies, and other domestic sectoral reforms can help discourage inefficient use of pesticides. Policies that facilitate farmer education and training programs as well as increase governments' ability to establish, monitor, and enforce appropriate regulations regarding proper pesticide use are also needed.


Excessive, deficient, or incorrectly proportioned doses of chemical fertilizer represent various forms of environmental risk. For example, too much fertilizer may result in residues contaminating local water supplies, including ponds otherwise available for fish farming. Conversely, too little fertilizer can result in low yields, declining soil fertility, and, eventually, soil exhaustion. The nonavailability or high price of fertilizer is more of a problem in Sub-Saharan Africa than in Asia or Latin America (Scott 1988a; Tardif-Douglin 1991). African farmers on average use less than a tenth of the fertilizer per hectare that Asian farmers use.

Inefficient use of fertilizer has been identified in diagnostic studies of potato production in a number of countries, including Bangladesh (Scott 1988a), Mexico (Biarnand Duchenne 1995), and Pakistan (Iqbal et al. 1995), and documented in farm surveys for cassava in Thailand (Howeler 1996). Improperly balanced fertilizer applications are of special concern in the case of cassava because so much of area planted is already produced on highly acid and infertile soils (Howeler, Oates, and Costa Allem 1999). The environmental and economic costs of nitrogen fertilizer use on R&T in developing countries have only recently become the focus of attention for researchers (Bowen et al. 1999). But based largely on an analysis and extrapolation of recent trends in nitrogen use in developed countries, Frink, Waggoner, and Ausubel (1999) suggest that farmers in developing countries, for example, China, are gradually ensuring that fertilizer applications conform to the proper proportions of nitrogen, phosphorus, and potassium.


Soil disturbance is a problem common to all R&T production (TAC 1997b). Regular working of the soil can degrade soils by decreasing soil carbon levels and fostering water and wind erosion. The effects can become accentuated as fallow periods decline and cropping intensity increases.

The degree of potential soil degradation is higher on hillside or highland fields where severe slopes can intensify the erosive effects of rainfall (or irrigation) and wind. Because some R&T are frequently cultivated on such fields - and cassava is grown on more marginal soils to begin with - the soil erosion associated with these crops can be substantial, though the association is not inevitable (see, for example, Howeler 1996; Howeler, Oates, and Costa Allem 1999). Although potato production in hilly areas can exacerbate erosion problems, some mid-elevation and highland cultivation of potatoes, particularly in Asia, is carried out in terraced fields otherwise used for irrigated rice. The latter form of potato cultivation causes less erosion. The case of sweetpotato is more complex, particularly for those varieties that produce abundant, rapidly growing vines (L-Velarde et al. 1997). This foliage can provide a quick crop cover over fragile fields and thereby naturally slow, if not reduce, soil erosion (Orno 1991).

As population increases in the countryside, and as the demand for food on and off the farm expands accordingly, cultivation of some R&T can also infringe on forests or high altitude natural grasslands, such as the paramos in the Andes. Expanded cassava production in northeast Thailand resulted in serious deforestation (Howeler, Oates, and Costa Allem 1999). A combination of better technology to increase net returns on existing farmland and policies that discourage cultivation of food crops in national parks, forests, and other preserves can prevent R&T-related degradation in these areas (see Duffy 1999).

Results of the COSCA surveys carried out in Cd'Ivoire, Democratic Republic of Congo, Ghana, Nigeria, Tanzania, and Uganda indicate that in Sub-Saharan Africa cassava production is replacing fallow land, and that cassava producers are cultivating their plots more intensively, that is with shorter fallows (Spencer and Associates 1997). The danger is that when the fallow period becomes too short, rapid soil degradation may result. One possible solution is to integrate small-scale livestock production and cassava cultivation more closely, so that cassava foliage serves as livestock feed and livestock manure provides organic matter to help sustain soil fertility (Christiaesen, Tollens, and Ezedinma 1995). Another possibility involves returning the leaves and stems to the soil (Howeler, Oates, and Costa Allem 1999). Furthermore, good agronomic practices such as closer plant spacing, reduced tillage, and use of contoured grass hedgerows can be very effective in reducing erosion and possibly increasing cassava yield and total income (Howeler, Oates, and Costa Allem 1999). The set of best practices is highly site-specific, requiring both the identification of appropriate, improved procedures through farmer participation and government initiatives such as land titles, educational programs, and credit schemes that provide incentives for adoption.

Potato cultivation in input-intensive crop rotation systems, like those involving irrigated rice in South Asia, has come under closer scrutiny because it extracts considerable nutrients from the soil. But preliminary research results suggest that the problem - from the farmer's perspective - may not be as acute as originally thought (Bardhan Roy et al. 1999). At least some farmers appear to grow potatoes in these systems in part because potato production halts continuous flooding and allows farmers to interrupt continuous rice production, which is associated with nutrient depletion, absence of soil aeration, and soil compaction (Pingali 1998).

Water and Air Pollution

The spread of pesticide or fertilizer residues into water supplies through irrigation systems or field run-off has attracted growing attention in recent years (see, for example, Ducrot, Hutson, and Wagenet 1998). Not only does this form of water pollution damage plants, insects, and livestock, it also poses a threat to the drinking water supply of farm households. The trade-off between food production, pesticides, and human health is most acute in the case of potato production, which relies on chemicals more than any other R&T (Antle et al. 1998).

Water pollution is not restricted to production, but also includes postharvest activities. Recent research on cassava processing in Vietnam highlights the adverse impact that a rapid increase in small-scale processing of cassava roots into starch has on local water supplies (Goletti, Rich, and Wheatley 1999; Howeler, Oates, and Costa Allem 1999). In the absence of proper treatment facilities, the water used in starch processing contaminates local water supplies. Similar pollution problems have also been noted in processing the Andean root crop, canna, into starch in Vietnam (Hermann, Quynh, and Peters 1999). With the expansion of potato processing in developing countries (Scott 1994a; Scott, Basay, and Maldonado 1997) and the construction of large-scale processing facilities to satisfy increasing demand and capture economies of scale, concerns have emerged about plant effluents. These problems mirror those associated with large-scale potato processing in some developed countries (New York Times 1994).

The sheer volume of water required to cultivate potatoes under desert conditions has also emerged as an issue, particularly in areas such as the newly reclaimed land in Egypt, where production and processing of potatoes are drawing on groundwater from newly dug wells (Chilver, El-Bedewy, and Rizk 1997). The possible medium- to long-term implications for local water supplies remain unclear.

Roots and tubers have also attracted attention of late for their potential role in the development of urban and peri-urban agriculture (see, for example, Brochier et al. 1992; Nweke et al. 1994). Given the increasing pressure on urban water systems in developing countries and the practice of using a wide variety of water sources to cultivate and process R&T in urban and peri-urban settings (see, for example, Villamayor 1991), the implications for local water supplies and human health merit closer monitoring (Howeler, Oates, and Costa Allem 1999).

Finally, some traditional cassava-processing techniques in West Africa can involve prolonged exposure to inhalation of smoke. Studies have shown that this can be hazardous to women's and infants' health. New, improved processing techniques for cassava have gone a considerable way toward reducing the time required to produce processed cassava products and hence toward decreasing environmental and human health problems (Jeon and Halos 1992).


A number of studies covering developed and developing countries have shown that as potato production becomes more technical, commercial, and oriented towards processing, producers have tended to reduce the number of varieties grown (Brush, Taylor, and Bellon 1992; Walker 1994). Similar concerns about the loss of genetic diversity in farmers' fields have been expressed about cassava (Howeler, Oates, and Costa Allem 1999), sweetpotato (Prain and Campilan 1999), and yam. The risk in the Andean region in particular - the center of origin for the potato and for several other R&T - is that more native varieties could go out of cultivation, only to be maintained in gene banks or lost forever (Alvarez and Repo 1999). One production initiative that not only enables small, resource-poor farmers to produce more food, but also increases the level of genetic diversity is botanical seed or true potato seed. With this technique, each seed is a genetically different entity (Upadhya et al. 1995). Hence, greater use of true potato seed would increase the number of different entities under cultivation.

The aroids such as taro, and the Andean roots and tubers such as canna or ulluco, present an even more formidable challenge. These crops have only recently attracted the attention of the global scientific community (NRC 1989). They are typically grown on a limited scale (Hermann and Heller 1997) and are often produced in heretofore isolated localities that can be threatened by rapid exposure to the full force of market penetration. Small, resource-poor growers of canna and ulluco may lack access to improved production and postharvest technology, credit to facilitate adoption, and related initiatives such as government-supported market promotion schemes, leaving them ill-equipped to compete with other food commodities produced on much larger farms and strictly for the market. As a result, these Andean R&T face the risk of extinction.

Increases in productivity will be a key requirement for improving the competitiveness of R&T in the decades ahead. One essential aspect of that effort will be the accelerated movement of germplasm across borders and between continents. For example, quicker transfer of germplasm native to Latin America to Sub-Saharan Africa would help raise cassava yields in the latter region (Spencer and Associates 1997). Concerns regarding protection of farmer's rights and national germplasm collections (see, for example, Schneider and Yaku 1996) can and must be addressed to ensure continued rapid transfer of materials between countries and regions.


The advent of genetically modified plants has become reality in the case of potato (see, for example, Qaim 1999) and sweetpotato (see, for example, Cipriani et al. 1999; Newell, Lowe, and Merryweather 1995; Prakash, Egnin, and Jaynes 1998). Although these innovations offer tremendous promise for both R&T production (reduced application of pesticides, for example) and use (reduction in the level of trypsin inhibitor in sweet-potato for feed, for example), they raise a whole array of new issues, ranging from unanticipated effects on the environment to the distribution of economic benefits from such advances. These questions potentially stretch across the entire food system, from preproduction, or seed stage, to final use. The range of concerns includes property rights for specific postharvest traits (for example, starch properties for cassava, sweetpotato, yam, or Andean roots and tubers), specific processing techniques, and as yet unknown uses of some parts of particular R&T plants. The limited knowledge and capabilities in most developing countries regarding the regulation, accelerated development, and subsequent introduction of these new technologies suggest that, as with cereals (Morris and Byerlee 1998), the response to this challenge will require a combination of new technologies, policies, and institutional strengthening, with a critical role for the international agricultural research centers (IARCs). Efforts are already underway in this direction at the international agricultural research system level with the formation of the Committee on Inter-Centre Root and Tuber Crops Research (CICRTCR) in the CGIAR. This committee is formulating plans for intercenter synergy in, among other things, the area of biotechnology (Scott et al. 2000). The plans include collaborative efforts to access laboratory facilities in developed countries, and thereby reduce the cost of developing biotechnology for developing countries, as well as studies of and methodologies for risk assessment of related technological innovations.

In summary, production and use of R&T in developing countries have drawn attention to the potential benefits and raised a series of concerns regarding their impact on the environment and human health. The available evidence indicates that the incidence of potential environmental effects varies from crop to crop. Pesticides and fertilizer use, for example, are much more important in the case of potatoes and problems of soil erosion more acute in the case of cassava. While the environmental problems discussed merit greater attention in the future, there are also clear signs that new technology, institutional innovations, and better policies can not only meet the challenge but also more effectively exploit the potential of R&T and thus help sustain the natural resource base.