Chapter 11: Pressures on the Environment from Agriculture
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11.2 Pressures on land and water resources
11.3 Global change issues
Chapter 4 sketched out the growth prospects and the main underlying parameters for the crop and livestock sectors in the developing countries. These prospects imply further intensification of land and water use. More mineral fertilizers and, to a lesser extent, pesticides will be used in the future. The progressive introduction of more environment-friendly technologies can only moderately attenuate growth in pesticide use in the next 20 years, but will not reverse past trends for growing use (see below). The projected growth path may be challenged therefore on a number of grounds concerning its environmental impacts and sustainability. Two related issues stand out in this regard.
First, what are the technological options for putting agriculture on to a more ecologically sound pathway while at the same time not only achieving the projected output, but also laying the foundation for sustainable agricultural development in the longer term? Second, given the inevitability of some tradeoffs between the environment and development in the medium-term future, what other actions are required to minimize them and ensure progress towards the objective of sustainable agriculture and rural development? These issues were at the heart of the debate at the 1992 UN Conference on Environment and Development (UNCED) and at the more technical meetings leading up to it, notably the 1991 FAO/Netherlands Conference on Agriculture and the Environment.
The first issue on technology is dealt with in Chapter 12, while Chapter 13 examines the wider, and in the main complementary, policy and institutional actions that are needed at the national and international levels to avoid or minimize the environment and development trade-offs. Examples of such actions are those for resource use planning, infrastructural development, farmer support services, and the wider ones affecting overall development and international economic relations. Several of these issues have been discussed in previous chapters. It remains for this chapter, which deals primarily with the developing countries, to describe and where possible quantify, the agricultural pressures on the environment that are implicit or explicit in the projections of the probable growth paths of the crop and livestock sectors.
11.2 Pressures on land and water resources
Competition for land and water
Competition for land between sectors and production systems is projected to intensify. It is expressed most accurately in the expansion of the use of land for arable and tree crops, shifting cultivation and grazing of livestock and its conservation under forest. Then there is the competition between crop and livestock production and, on a much smaller scale, between crop production or mangrove swamp preservation and aquaculture; and, as noted in Chapter 5, there will be further pressures on the forest for timber and fuelwood extraction. Finally, increasing population and economic growth will contribute to further diversion of land to human settlements and infrastructure.
Forest land loss to agriculture is primarily a tropical rather than a temperate zone problem (see Chapter 5). In the former, deforestation rates are currently about 15.4 million hectares a year, of which a large part is thought to result from extension of grazing and cultivation, particularly shifting cultivation, a considerable proportion of which will eventually revert to bush and then tree fallow. In the temperate zone, shifting cultivation is no longer a significant feature of agricultural production systems and in many countries net afforestation, either naturally or through plantations, is taking place. For example, China has a considerable programme of afforestation (People's Republic of China, 1992).
It is possible that the rate of deforestation would slow down for a number of reasons. First, the lagged effect of recent policy improvements: for example, those to remove incentives and tax distortions favouring deforestation or to strengthen the controls on logging practices. Second, the increasing scarcity of forest land in the right locations suitable for arable cultivation. Third, the projected slower growth of the population dependent on agriculture in the developing countries. Fourth, technological improvements which meet agricultural demands through land intensification rather than land expansion. Fifth, the adoption and implementation of sustainable agriculture and rural development policies and programmes. And sixth, policy changes in some financing institutions which are adopting more rigorous environmental impact assessments of investment projects.
These reasons are not, however, going to be sufficient to reduce the pressure altogether. Even if current rates of deforestation are considerably reduced, significant areas of tropical forest are likely to be converted to some form of agricultural use during the next 20 years or so. As noted in Chapter 4, some 90 million ha of additional land may come under crop production by year 2010 in the developing countries, excluding China. This is a small part of the 1.8 billion ha of land with crop production potential not used now for agriculture. However, it is estimated that at least 45 percent of the latter land overlaps with forest and the real overlap is probably much larger.
This continued pressure highlights two priority actions which are considered in Chapters 12 and 13: greater emphasis for agricultural research on sustainable alternatives to shifting cultivation; and a more holistic strategy for tropical forest conservation such as that sought by the FAO Tropical Forests Action Programme, since current forestry policies have tended to treat the deforestation problem as a forestry problem in isolation from a better understanding of the reasons for agricultural intensification and as a consequence have commonly failed. In addition, emphasis on wider rural development and agrarian reform could contribute to the slowing down of migration into marginal, environmentally fragile areas.
Crop production in dryland areas (land class 'dry semi-arid' in Table 4.4) is projected to expand by 6 million ha, a relatively small figure. However, much of this land is currently rangeland and its conversion carries the risk of either increasing grazing pressure on the remaining pastures or displacing livestock on to even more marginal land, which must be managed carefully if degradation is to be avoided.
The competition of aquaculture for land may not be very significant quantitatively, because the areas involved are generally quite small. It can, however, be highly important qualitatively, because in some countries the land being developed is relatively unique mangrove swamp, with potentially valuable biogenetic resources and an ongoing role as a breeding ground for coastal fisheries. No projections have been made of the total area at risk, but specific studies for key localities suggest that major losses could continue during the next two decades unless greater protective measures are taken.
Finally, moving on to the competition between agriculture and human settlements, including urban/industrial and infrastructural development, there are a number of unknowns that make it difficult to be emphatic on the magnitude of the pressure, yet there are clear grounds for adopting the precautionary principle, which is embodied in the Rio Declaration.
Between 1990 and 2010, the population of the developing countries is projected to increase by about 1.8 billion, but there is great uncertainty about how much land these people will occupy. Economic growth, industrialization and continuing urbanization will further increase pressures for expansion of land under human settlements. The tentative and very speculative projections presented in Chapter 4 place the additional land to be occupied by human settlements in the period to 2010 in developing countries (excluding China) at about 34 million ha, of which nearly 20 million ha would be land with agricultural potential (Table 4.3). This is only a small fraction of the 1.8 billion ha of land with agricultural potential.
Thus, for the developing countries as a whole, land loss to human settlement appears not to be a substantial threat - a modest improvement in the productivity of the existing land or a small addition from the land not yet used for agriculture could compensate for the loss. But the aggregate picture is misleading (Norse et al., 1992): first, because some countries have little or no additional land; second, much of the urbanization tends to be in areas with high quality soils, while the land not in agricultural use tends to have poorer quality soils; third, the population of the developing countries will continue to grow well into the second half of the twenty-first century, causing the possible loss of further substantial areas, which once built on would be lost for ever. The situation in coastal areas of many small island countries is particularly critical because of the pressure on land from tourism. And of course the problem does not end here, because expansion of human settlements is not the only factor causing land loss. Degradation, for example, is causing both land loss and reduced productivity over a far wider area (see below). Long-term global warming and climate change also could threaten as much as one-half of the high quality land resources of some countries through sea level rise or deterioration in agroecological conditions, e.g. in Bangladesh or the Gambia. These facts are put forward as justification for the above conclusion that the precautionary principle should be applied so as to minimize the loss of land to human settlement, and this notwithstanding the contrary possibility that some developing countries will be able to follow the pattern now exhibited by many developed countries, namely the reduction in arable area as a consequence of successful intensification. The zoning and other land use planning policies required are discussed in Chapter 13.
The combined effect of population and economic growth will exert even greater pressures on freshwater supplies than they will on land (Falkenmark and Widstrand, 1992). Chapter 4 indicated that technological growth would generally continue to make it possible to increase agricultural production with relatively modest expansion of the land in agricultural use. This, however, has not been the experience to date with water consumption, and major improvements in water use efficiency are unlikely in the medium term. Though technological progress has raised water use efficiency in a few areas, it has been insufficient to compensate for income growth and wasteful consumption patterns which collectively can cause a manifold increase in per capita water demand for non-agricultural uses (Table 11.1). The future need not be like the past, but technological improvements and changes in consumption patterns seldom take less than 15 years to have an appreciable effect, and generally the time lag is much longer.
These facts have serious implications for the next two decades and beyond. Africa and Asia already show a worsening shortage in per capita freshwater availability, although much of Latin America is well endowed (Table 11.2). Many countries are already closer to their water supply limits than to their land limits, and the need to increase the agricultural production will accentuate pressures on the water resources. Three aspects are of particular importance.
Table 11.1 Sectoral water withdrawals by country income groups
|Annual withdrawals percaput (m3)||Withdrawals by sector|
Source: Reproduced by permission from World Bank (1992a: 100), based on data from the World Resources Institute.
First, food supplies in the developing countries are already heavily dependent on irrigated cereals production, which accounts for about one half of the total production of cereals. This dependence is projected to grow somewhat, in spite of the high cost of irrigation in some countries and the pressures to remove the subsidies (hidden or open) on existing irrigation, which will become increasingly difficult to justify on economic grounds.
Second, the growing water demand for irrigation and the rising industrial and domestic demand will increase competition for water and could push up its price beyond a level that is profitable for staple food production in some areas. Agriculture is the dominant water user, accounting for nearly 70 percent of total consumption of managed water resources, compared with about 21 percent and 6 percent for industrial and domestic use respectively. The latter users are commonly in the situation where they can only expand their consumption of water by 'taking" it away from agriculture, and can generally afford to pay more for it than agriculture. Third, overextraction of groundwater is a growing problem in many areas. It is most acute in the Near East, where it is leading to salt-water intrusions that ultimately make the water unsuitable for crop production. But it is also a problem in large areas of South Asia, where food security is heavily dependent on irrigation. Over pumping in these areas is causing water levels to fall beyond the reach of shallow tubewells with the risk that irrigation may eventually become too expensive or physically impractical (see Box 11.1). Finally, the supply problem will be intensified by degradation of existing irrigation systems to the point that they have to go out of use, and deterioration of water quality (see below).
Degradation of land and water resources
The effects of existing degradation, notably erosion, nutrient mining, salinization of soils and contamination of water, are included implicitly in the production analyses of this study because the base year yields and fertilizer response ratios reflect the productivity effects of such damage. Less tangible problems, like desertification and forest degradation, are not included.
Box 11.1 Groundwater mining
Much of the successful expansion of irrigation in recent decades has come from the exploitation of groundwater using tubewells. They have the advantage of small scale, low cost and rapid construction without the loss of fertile land and the destruction of human settlements commonly associated with large-scale, gravity fed schemes based on reservoirs. The expansion has been very rapid. In India alone, the number of tubewells jumped from nearly 90000 in 1950 to over 12 million in 1990. Behind this success, however, is the neglect of the fact that agricultural development based on groundwater is unsustainable, when it uses "fossil" water or when extraction rates exceed rates of recharge.
The rapid expansion of tubewell irrigation has put extreme pressures on what is commonly a static resource because natural rates of recharge are low. Moreover the problem has been intensified by pressures that are generally some distance from the site of extraction, largely through deforestation in upland watersheds, or overgrazing and other forms of land degradation that accelerate runoff and reduce rainfall infiltration. Consequently, water tables are dropping and causing a wide range of environmental, economic and social problems. Saline intrusions are becoming a problem in many coastal regions. Over-pumping has led to increased investment or operating costs as falling water tables have necessitated deeper wells and greater energy consumption for pumping. In some instances poor farmers without the capital to deepen their wells have had to revert to rainfed production. In others the necessary adjustments have been too late and the land has been decertified, as in some places in India.
The magnitude of the current extent and intensity of degradation has recently been estimated using a standardized methodology-the Global Assessment of Soil Degradation (GLASOD) - and is more defensible than earlier calculations that pooled the results of diverse national and regional assessments without common definitions and methodologies (ISRIC/UNEP, 1991). Soil erosion is by far the most widespread cause of degradation, with water erosion being the principal agent (Table 11.3). Of greater consequence still are the estimates of the intensity of degradation. Nearly I billion ha of arable land in developing countries are estimated to be so degraded that productivity is being moderately or severely affected. Some 9 million ha worldwide, of which 5 million ha are in Africa, have had their original biotic functions fully destroyed and reached the point where rehabilitation is probably uneconomic.
Table 11.2 Per caput water availability by region, 1950 2000 ('000 m3)
Source: from FAO (1993d), based on Ayibotele (1992).
Table 11.3 Soil degradation by type and cause (classified as moderately to excessively affected) (million ha)
|Regions||Water erosion||Wind erosion||Chemical degradation||Physical degradation||Total (million ha)|
|North and Central America||90||37||7||5||139|
|Mismanagement of arable land||24||16||58||80||339|
Source: Adapted from ISRIC/UNEP (1991).
More recent information suggests that the estimates of the extent of land degradation and its effects on productivity as reported in GLASOD have been exaggerated in a number of cases. At the same time, however, the effects of land degradation are often masked by the compensating effects of improvements in agricultural technology or increasing applications of plant nutrients so that yields may have been increasing even on degrading land. Also in some cases, farmers and rural communities in some areas of Africa and Asia have demonstrated that land which GLASOD classifies as unrestorable can in fact be rehabilitated. Thus, for example, farmers in Kenya (see Chapter 12) and China have rehabilitated formerly abandoned or heavily degraded land at modest cost given appropriate incentives and technologies, though the conventional approaches assumed by GLASOD would probably have been uneconomic.
The production projections assume some changes in national policies and farm practices to correct part of the soil/water degradation, though the full benefits of such changes will not be felt in the short term. Thus some degradation is assumed to continue. However, projections of future degradation and its consequences, particularly its impact on productivity, are very difficult to make as discussed below.
There is widespread evidence of erosion resulting in losses greatly in excess of 50 tonnes of soil per hectare per year, losses that may be five or more times the natural rate of soil formation. The impact, however, of such losses OD crop yields or production has not been well established in physical terms though there have been many attempts to do so. The relationship between erosion and productivity loss is more complex than previously thought, as is that between man-made and natural erosion. Similarly, the experimental techniques once used to quantify these losses are less effective than previously thought. The relationship between soil erosion and yield loss is not linear, i.e. it is not directly proportional to the thickness of the layer lost, nor to the type of particles lost. Moreover, the impact on soil structure, particularly the impact on the size of the air spaces, can be more important than that on its chemical composition. Mitchell and Ingco (1993) and Crosson (1992) report that a number of studies on the relation between land degradation and losses in crop yields conclude that such losses are probably of minor importance, being in the order of 2 to 4 percent over very long periods (up to 100 years). All these studies, however, refer to the generally deep, fertile soils in North America. Their conclusions cannot be simply transferred to other regions, mainly because tropical soils and biological processes in them can be very different from those in the temperate zone soils. Where soil fertility is mainly concentrated in the surface layers, soil erosion can lead to greater yield losses than those estimated for the temperate zones.
It is also possible that yield loss in one area may be compensated by gains further down the slope, valley or plain, where the soil is eventually deposited. Though here again the issues are not straightforward: first, because deposition may also have negative external consequences, e.g. where it silts up reservoirs and irrigation canals and reduces their effective life (Table 11.4); second, because man has commonly been blamed for much of the silt load of rivers, whereas it is now considered that a substantial proportion results from upward and ongoing movements in the earth's crust. In China, for example, whereas the severe erosion of the loess plateau was once attributed largely to man's activities, and is still presented in these terms by some observers, it is now thought that over 60 percent of the erosion is due to such movements.
Soil nutrient mining
This is an issue brought into prominence by the ongoing debate on environmental accounting. The shortening of fallows and prolonged crop harvesting without adequate technological responses to replace the soil nutrients taken out by crops with organic or mineral fertilizer inputs, leguminous crops, nitrogen-fixing algae and so on (see Chapter 12), is lowering the nutrient status of soils and the actual or potential crop yields. It consequently threatens the sustainability of agricultural production. Part of the problem is often masked by the gains from unbalanced fertilizer use, which although it raises yields, also introduces an additional economic cost because the lack of balance lowers the technical efficiency of the mix of fertilizer nutrients (Twyford, 1988).
Table 11.4 Siltation of selected Indian reservoirs
|Reservoir||Assumed rate (acre-feet p.a.)||Observed rate (acre-feet p.a.)||Expected life as % of designed life|
Source: Data from Central Water Commissioner, Ministry of Water Resources, Government of India.
The situation is serious in many countries but most acute in sub-Saharan Africa, both for major nutrients like nitrogen and phosphate, and for micronutrients like boron and manganese. In the mid-1980s all countries in the region were estimated to be suffering from nutrient mining to a greater or lesser degree (Smaling, 1993), with the most serious problems occurring in semi-arid areas where livestock manure is in short supply and the use of mineral fertilizers is seldom economic. The projected situation shows some improvement but the time horizon to 2010 is too close to remove the main gaps in technology and infrastructure. These constraints are examined in Chapters 12 and 13 respectively. In particular there is the need for better and less costly integrated plant nutrient systems and improved transport and marketing systems to lower relative mineral fertilizer prices, and provide incentives for more sustainable agricultural practices.
Salinization of soils
This is primarily a problem of irrigated areas, but also occurs in hot dry zones where strong evaporation brings salts to the surface. In irrigated areas it is usually the consequence of bad design causing poor drainage, and/or inadequate maintenance and inefficient management leading to excessive application rates, and seepage from water courses. The end result is waterlogging, salinization, depressed crop yields and eventually, if corrective action is not taken, loss of land for agriculture. This leads to physical pressures on the finite resource base if land is permanently lost, which according to some estimates may vary in the range 0.2-1.5 million ha per year worldwide, while some 10 to 15 percent of irrigated land is to some extent degraded through waterlogging and salinization.
The production projections of this study assume a net increase in irrigation of 23 million ha in the developing countries, excluding China (Table 4.5). They also assume that appropriate measures, described in the next two chapters, will be taken so as to prevent further losses of existing irrigated land through salinization. There is some validity for such an assumption in that there is now greater emphasis on improved water management and drainage, but the required investments and institutional changes will take a number of years to mobilize. As noted in Chapter 4, gross investment in irrigation would need to be much above that implied by the net addition of 23 million ha, in order to account for the rehabilitation or substitution of irrigated land subject to degradation.
This can be broadly defined as land degradation in dry land areas. Much of the attention has been on Sudano-Sahelian Africa where the deserts were once reported to be steadily advancing, though such reports are now challenged (see below). It is not, however, just an African problem. All the major continents face desertification problems and the area of cropland and rangeland prone to desertification is estimated at 30 percent of the world's land surface.
A major shift in scientific thinking on this topic has occurred in recent years, with a growing consensus for the view that the area affected by desertification has been greatly overestimated (see, for example, Nelson, 1988; Warren and Agnew, 1988; Bie, 1990). FAO has placed particular emphasis on the weakness of the methodology used to produce some of the more extreme estimates. It is now recognized that drylands are much more resilient to drought and to man's abuse than previously thought.
Although man's role in desertification is still not well understood, there is little doubt that soil nutrient mining and the overcultivation of fragile soils does lead to dryland degradation and desertification. The projections of Chapter 4 point to increasing pressures of this type. Mitigation of these pressures will be dependent on improvements in farm practices, such as soil moisture conservation, and the development through research of leguminous live mulches and other techniques (see Chapter 12).
The future water supply is threatened both by the quantitative constraints examined above, and qualitative problems arising within agriculture which are a threat to crop yields and to human, livestock and wildlife health. The principal threats of agricultural origin are the following: rising salt concentrations in irrigated areas; fertilizer and pesticide contamination of surface and groundwater; and discharges of organic effluents from intensive livestock units and fish farms. All of them are projected to increase, because of the long length of time required to achieve appropriate corrective actions.
The intensification of irrigation could raise the degree of water reuse, and hence the build-up of salt concentrations, with risks to crop yields and to the sustainability of irrigation if corrective actions are not taken. Fortunately the main irrigated cereals, rice and wheat, are relatively tolerant to low or moderate salinity, but are subject to yield losses of about 10 percent at high salinity levels.
Greater applications of organic and mineral fertilizers are essential to prevent soil nutrient mining and raise crop yields, but in many developing countries application will remain below that likely to cause major pollution problems. However, in some areas with either very high application rates (for example the Punjab) or thin sandy rock strata above aquifers (as in parts of Sri Lanka), the risks could be significant if corrective measures are not taken. Per hectare application rates of mineral fertilizer in some countries of Near East/ North Africa and South Asia are projected to exceed 100 kg of nitrogen, so that by 2010 heavy rates will have been applied for 20 to 30 years or more. This is the time span over which the developed countries started to face severe groundwater nitrate problems, underlining the importance of adjusting application rates to the rate of uptake by plants. Restrictions on the use of agricultural chemicals and on the disposal of wastes from agroprocessing to protect water quality for increasing human consumption, will necessarily impose costs on consumers.
Intensive dairying, pig and poultry units are projected to account for an increasing proportion of total livestock output, and so their effluents will also grow. Many developed countries have introduced measures regulating the storage and disposal of such effluents. Livestock concentrations are strictly regulated in the areas of permeable sandy soils in the Netherlands, for example. The situation in the developing countries is likely to worsen before similar measures begin to be taken there.
The production projections of this study imply three changes that, in the light of the past approaches to pest control, could pose serious threats to the environment. First, the further reduction in the length of fallow periods may not only endanger soil fertility as noted above, but in the absence of suitable corrective actions, could lead to more serious and more frequent weed, insect and disease attacks because the causal agents are able to survive in greater numbers from one cropping season to the next. Second, the increase in the area of land carrying two or even three crops a year could have similar effects as the reduction in fallow periods. Finally, the rise in the demand for vegetables, and to a lesser extent fruit, could lead to greater pollution and health risks from excessive use of insecticides. These crops tend to receive excessive applications of insecticides and often too close to harvest, either as an insurance against the risk of loosing a high-value crop or in order to improve their cosmetic appearance and hence their price. Such excessive application rates can pose numerous risks to the people applying them, to consumers, to natural predators of pests and to drinking water supplies.
It is difficult to project the future rates of pesticide use in any detail. It is assumed, however, that a combination of greater emphasis on integrated pest management (IPM) and biological control methods in general, and concerns about public health risks and ecosystem protection, will continue the present trend for a slowing down in the overall growth rate of chemical pesticide use, and a reduction in both the rates of application and the toxicity of insecticides and pesticides in general. These positive trends are evident, for example, in Egypt which has banned the use of a number of toxic pesticides, and Indonesia, where the successful introduction of integrated pest management on rice has brought widespread benefits (see Chapter 12).
Consequently, it is a reasonable assumption that the future growth rate of pesticide use will be lower than that of the past two decades, and that there will be a reduction in the environmental risks per unit of pesticide use. Thus, while the concerns expressed by certain groups are important, and there are no reasons for complacency, there are no grounds for arguments based on linear extrapolations of past mistakes.
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