4. POTENTIAL ENVIRONMENTAL IMPACTS OF THE SUPPLY OF CONCENTRATE FEED COMMODITIES

4.1. Components and features of potential environmental impacts

4.1.1. Types of potential impact

The potential environmental impacts of the supply of concentrate feeds include impacts of the various stages of crop production, trade and processing of feeds. Potential impacts of crop production, and the expansion of production, include effects on land-use (including deforestation, change in amenity value of land, change of habitats and impacts on biodiversity); direct effects of cropping on soils (soil erosion and fertility), water (use of water resources and impacts on run-off and drainage waters), and air (air quality and greenhouse gas production); and indirect effects of the production and supply of inputs to agriculture (mechanisation, fuels, fertilizers, pesticides, etc).

Potential impacts of trade and processing of commodities include direct effects (mainly on air and water) due to transport, storage and processing (eg wastes and effluents), and indirect effects of input supplies as above.

The utilization of concentrates for feeding livestock clearly creates a further range of potential environmental impacts, particularly the impacts of large numbers and concentrations of livestock in intensive enterprises. These impacts are discussed in other reports in this series. However, the utilization of feed concentrates does potentially have some wider positive environmental impacts which should be noted. These include the impacts of the greater efficiency of overall feed use which concentrate feeding may promote, such as allowing better use of poor quality waste and roughage feeds (straws, stovers, crop processing wastes), some of which might other wise be wasted, and reducing methane outputs per unit of product from ruminant animals. Greater efficiency allows the production of more consumable livestock product from fewer animals, which may in some circumstances allow reduced pressures on other resources (such as grazing lands or other feed resources, eg trees), or increased production and income from livestock products (see Cheeke 1994).

4.1.2. Special features of potential impacts of feed concentrate supply

Two special features of the supply of feed concentrates are notable in determining the potential environmental impacts of livestock production systems. These are that:

Many feed commodities are joint or by-products of crop production enterprises; environmental impacts are thus not solely attributable to the demand for feed concentrates (eg food cereal brans, oilmeals, cotton seed cake, molasses). Production methods and impacts will generally be determined by demand for primary products.

Environmental impacts of the demand for concentrates are often remote from the livestock production enterprises generating that demand (especially for intensive livestock enterprises), and usually not under the same project or enterprise management. Thus, crops providing feeds may be produced in different farming systems, geographic locations, agro-ecological zones, or in different countries and continents in some cases. Feed crops in these circumstnces are thus produced as cash crops in response to local market conditions and there is no necessary link between specific livestock production systems and the types, intensities or locations of crop production, or the environmental impacts of that production. Tracing the chain of cause and effect in environmental impacts is complex in such cases.

Additional general features to be noted are that:

Environmental impacts may be both positive and negative; the outcome in specific cases will depend on a complex of factors affecting crop production including the basic land resources available, production systems, technologies and inputs adopted, prevailing socio-economic and regulatory environments and many other factors (as outlined in Section 4.1.3. below)

All types of land-use have potential environmental impacts; what is of concern in assessing the impacts of alternative uses are the relative or net impacts and trade-offs of losses and gains.

Thus the impacts of increased demand for concentrate feeds may be the small net impacts of a slightly changed cropping system (eg where opportunities for expansion of cropped areas are limited), or the net impacts (gains and losses) of changed land-use where new cropland is opened up.

4.1.3. Factors affecting potential environmental impacts of supply of concentrate feed

The environmental impacts actually caused by the supply of particular feed commodities depend on a range of factors determining the production environment, including:

The nature of the natural resource base and climate
Prevailing cropping systems and intensity
Specific features of the crop grown
Available technologies and inputs
Socio-economic conditions, and
The environmental policy and regulatory framework

Natural resource base The impacts of cropping are related to the nature of land resources cropped (topography, soil type, land capability), previous land-use (cropping systems, vegetation types, habitats), the availability of water resources (for irrigation), and climate (determining agro-ecological zones and crop suitability). An important factor affecting potential environmental impacts is the extent and intensity of cultivation of marginal croplands (ie land with some features which limit crop yield and which may be more susceptible to damage by inappropriate cultivation); expansion of crop outputs in some countries will entail increased use of these marginal croplands.

Cropping systems and intensity Cropping systems vary from slash and burn or fallow rotation systems through varying degrees of intensification to highly intensive multiple cropping systems under irrigated conditions or the high-input/output monocrop annual cropping systems of the temperate developed regions. Feed commodities tend to be produced in the more intensive systems, though by-product feeds such as cereal brans and oilcakes can be produced in less intensive systems. The nature and degree of environmental impacts of cropping vary considerably between these systems. Key elements of changes in cropping systems that will influence the types of environmental impacts incurred are increases in cropping intensity (increased frequency of cropping) and attempts to increase unit area yields (by increased inputs or improved crop husbandry).

Crops grown Crops differ in specific features that may affect environmental impacts. Perennial crops such as some oil crops (oil palm, coconut) may have lesser impacts than some annual crops. Crops typically grown in more fragile environments may generate greater impacts than others (eg cotton, sorghum and millets grown in semi-arid areas prone to soil erosion). Crops requiring higher levels of inputs may lead to greater impacts if not well managed (such as cotton, maize and temperate high yielding cereals).

Available technologies and inputs Environmental impacts depend critically on the technologies, inputs and crop management practices adopted. Management systems vary from exploitative low-input systems to closely managed systems with appropriate cultivation (eg minimum tillage), integrated pest management (IPM) and targetted fertilizer inputs. Technologies are available for many different environments to conserve soils, soil fertility and organic matter, soil moisture and water resources, and to minimise the use of, or impacts of, inorganic fertilizers and pesticides. The adoption of these technologies is dependant on a wide variety of socio-economic factors.

Socio-economic conditions Socio-economic factors such as the relative availability of land, labour and capital, access to input supplies, technology information, extension and markets, and relative market prices of different crops and livestock products, and many other factors strongly influence the types of cropping systems and technologies adopted, crops grown and likely environmental impacts in different localities. These factors are in turn influenced by the complex of macro-economic, policy, international relations and trade conditions that set the framework and incentive/disincentive structures in which farmers make production decisions. Incentives and disincentives determined by socio-economic policy provide an important potential tool for encouraging an appropriate combination of environmental practices together with national and local production, consumption and economic objectives (though there are few circumstances yet in which the effects of such policy instruments are sufficiently well described or understood to be applied more widely).

Environmental policy and regulatory framework Land-use, cropping practices and potential environmental impacts may also be influenced by environmental policies and regulations. In some cases traditional indigenous regulations still exist to protect certain environmental features, though increasingly overtaken by population pressures and replaced by state and international policy and law. Many developed countries now have regulations controlling land-use and agronomic practices in some ways, including protection of habitat reserves, forests and wetlands, protection of landscape features, restriction of cultivable areas at risk of damage (eg erosion), enforcement of soil conservation measures, control of water use, control of the types and methods of use of pesticides and other inputs, restriction of pesticide residues, limitation of soil nutrient effluents in water courses, control of crop residue disposal methods (eg straw burning), and others. Improved understanding of cause and effect in environmental impacts, and the growing interests of wider sectors of societies will lead to further development of such measures, while monitoring, enabling policies and enforcement methods are also under development to encourage compliance. Developing countries are increasingly enacting similar regulations.

It is clear from the above considerations that the environmental impacts of production of a particular crop, or the likely impacts of changes in cropping, vary between locations depending on specific prevailing circumstances. Environmental impacts are thus site specific. Environmental monitoring practices and project or policy planning guidlines will clearly also need to reflect these circumstances, as outlined in Chapter 5. A critical problem is that identification and development of monitoring methods for indirect indicators of environmental impacts (eg relative prices of food and feed crops or of feed commodities and livestock products) may also need to be site specific. Monitoring methods will be more generally applicable if based on the common basic components of the environment (ie land/soils, water, air and biodiversity).

4.2. Relative importance of feed production and trade in the context of all cropping and food trade

The following sections aim to outline the relative importance of the production and trade in feed concentrates as proportions of total crop production and trade, as an illustration of the potential scale of significance of any environmental impacts of feed concentrate supply. First the scale of feed commodity production is placed in the context of overall crop production and current land-use, on global and regional bases, and for major individual producing countries. Secondly the scale of international trade in feeds is examined in the context of both 'production-for-trade' and of total trade in commodities.

4.2.1. Areas cropped for feeds as a proportion of all arable land

Table 26 illustrates the proportions of total arable land cropped to provide concentrate feeds in 1990/92 (derived from the areas cropped under each commodity group, as shown in Appendix 5 Tables 4 to 7, adjusted by the proportions of commodity production used for concentrate feeds as shown in Appendix 5 Table xx). At the global level, an annual average of 15% of total arable land was cropped for coarse grains destined for concentrate feeds in 1990/92. A further 5%, 10% and 1% was cultivated for feed wheat, oilseeds and roots and tubers respectively. An overall global total of 31% of arable land was thus cultivated for feeds, or 21% if it is assumed that all oilseeds would have been cultivated for oil in any case.

Table 26 Areas cropped with coarse grains, wheat, oilseeds and roots and tubers used for livestock feed as percent of total cropped areas by world regions in 1990/92

Source: Analysis of USDA PS&D data for coarse grains, wheat and oilseeds and FAO Agrostat data for roots and tubers

1. Total arable land under annual crops, as defined by FAO (from FAO SOFA database)

2. Derived from areas cropped and proportions used for feed as shown in Appendix 5

3. World regions as defined in Appendix 1

4. Percent of total arable area cropped to coarse grains, wheat and roots and tubers used for livestock feed (NB excluding oilseeds which would be grown in any case for oil)

At the regional level, proportions of arable land cultivated for feeds were highest for developed regions, particularly in EE and CIS (31%) and in WE (28%) but were generally lower for developing regions, particularly in SSA (0.3%) and S Asia (2.4%).

These data suggest crudely that the environmental impacts of feed commodity production amount to about 21% of the global total impact of cropping (assuming that the impacts of production for feed are similar to those of production for other purposes). While this is a significant proportion, it will clearly be more important to focus attention on cropping for non-feed production in order to monitor and control any environmental impacts of cropping. Other implications of the table are that the priority focus among feed-crops is likely to be coarse grains, which comprise three quarters of the global area cropped for feeds, and that wheat production for feed is of significance only in developed regions (5-11% of total cropped areas).

The significance of feed crops as sources of potential environmental impacts is greater in some individual countries. Table 27 shows the proportions of total arable areas devoted to feed crops (coarse grains plus wheat, and oilseeds) in major producing and exporting countries. For coarse grains and wheat, major developed producing countries such as the EC-12 and Canada have up to 25 and 28% of cropland in grains for feeds. In most other countries, proportions of land cropped in feed grains is less than 20%. Oilseeds occupy up to 32% of arable land in Argentina and 24% in Brazil; probably more than 90% of this production is processed for oil (either domestically or in importing countries) and provides oilmeals for livestock feeds; most of this production would probably be grown for oil if there was no demand for oilmeal feeds.

Table 27 Proportions of total arable land devoted to coarse grain, wheat and oilseed crops for concentrate feeds in selected countries

Source: USDA PS&D data on areas cropped and proportions of production used for feed (coarse grains and wheat); FAO SOFA data on total arable land under annual crops

1. Estimated from total areas cropped with maize, barley, oats, sorghum, millet and wheat, multiplied by proportions of crop used for animal feed domestically (NB this may underestimate feed crop areas for countries exporting to feed consumers.

2. Total areas cropped with all oilseeds

4.2.2. The potential significance of trade in concentrate feed commodities

Table 28 shows gross exports of commodities which may be used as feeds (coarse grains, wheat, oilseeds and meals, and roots and tubers) as proportions of total production and consumption of these commodities at the global level (derived from regional data tabulated in Appendices 5 and 6). Annual global gross exports of coarse grains, wheat, oilseeds, oilmeals and roots and tubers (for all food, feed and industrial uses) in 1990/92 comprised a relatively small proportion of production, generally less than one fifth except for oilmeals. Gross exports for feed use only were even less significant, ranging from 2 to 8% of total production (again except for oilmeals). As a proportion of total feed consumption, however, trade was more significant, comprising 15% of the global total.

Thus, the majority of feeds produced are consumed within regions or countries of production (except for certain major exporting countries - see below). Production of feed commodities for international trade comprises only a very small proportion of total commodity production and any environmental impacts generated by this production are relatively insignificant compared to potential impacts of total feed crop production as outlined in Section 4.2.1. above (though note that even total feed production is a relatively small proportion of total crop production). Any environmental impacts of the international trade itself (eg through transport) may also be small compared to any impacts of production. There will of course be additional transport of commodities for in-country marketing.

Table 28 Global total trade in feed commodities in 1990/92

Feed-use estimated on basis of USDA PS&D data (see Table 27)

1. See Appendices 5 and 6 for regional data and definitions

2. Production of oilmeals refers to production of residues after crushing

3. Amounts traded as percentage of total amount of commodity used as feed (see Table 4, Section 2.4.1.)

Trade is clearly more important for certain regions and countries than the global averages indicate. Countries with significant quantities of exports, and which export relatively high proportions of their production, are summarised in Table 29 below. These countries may be expected to be most at risk of environmental impacts of the demand for feed concentrates, and would be priority targets for any monitoring or case study of impacts of trade. (Note, however, that the figures in Table 29 refer to exports for all uses; data are not available to distinguish the end-use of exports from individual countries)

The amount of international trade in crop commodities conducted for feed uses is not distinguished in international databases. The best assumption may be that the proportions of international trade conducted for feed-use are the same as the proportions of overall consumption of each commodity for feed, as indicated in Table 25 Section 3.2.4. Thus, at the global level, international trade for feed purposes may be estimated to represent 66% of total trade of coarse grains (by weight). Equivalent figures for wheat, oilseeds, oilmeals and roots and tubers are estimated as 21%, 11%, 94% and 26% respectively of total trade in each commodity. In terms of proportions of the total international trade in all concentrate feeds, coarse grains comprised 46%, and wheat, oilseeds, oilmeals, and roots and tubers 17%, 3%, 27% and 7% respectively in 1990/92 (see Table 28 above). Coarse grains and oilmeals thus constitute the bulk of this trade. Any environmental impacts of transport and storage will be mainly due to these commodities.

Table 29 Summary list of major exporting countries ranked by annual quantities of commodities exported in 1990/92

Sources: USDA PS&D data, see Tables 19 to 23

1. Ranked by quantities of annual gross export in 1990/92; including countries with net exports at least 1% of world total trade; note quantities exported may be for food, feed and other uses

2. Production of oilmeals refers to product of crushing for oil (may be partly derived from imported oilseeds).

4.3. Environmental impacts of feed concentrate commodity supply

4.3.1. Impacts of crop production

Crop production potentially impacts on various components of the environment, including, land resources, landscape, soils, water, air, biodiversity and human health. Table 30 outlines some of these impacts. Impacts on land resources for example, may include changes in land-use (forests, grasslands, croplands and habitats), changes in the use of marginal croplands, and changes in use of water resources. Impacts on soils include aspects of soil erosion, fertility and other soil conditions. Following sections review the nature of the main impacts listed in Table 30.

Table 30 Potential impacts of crop production on components of the environment

4.3.2. Changes in land-use and land resources

Cropland use, cropped areas, cropping intensity and yield Increased crop production may be derived from expansion of cropped areas and/or intensification of production through increased cropping intensity or increased use of inputs to raise crop yields. Increased cropping intensity results from more frequent cropping, either through increased double cropping (eg. under irrigation) or reduced fallow periods in less intensive systems. Projected increases in overall crop production in developing countries to 2010 are estimated by FAO (1993) to be derived from increases of 12% in agricultural land in use, 8% in cropping intensity (from 79 to 85%) and 37% in average yields. These changes in cropland-use or cropping systems have different consequences for impacts on the environment.

The relative importance of these changes differs somewhat between world regions, depending mainly on the availability of additional land with agricultural potential. Recent trends in developed and developing world regions are reviewed in Section 3.2.1 and Appendix 5. Table 31 shows the current utilization of land with agricultural potential (as defined by FAO 1993) in developing countries. Regions with capacity for expansion of crop areas include SS Africa, Latin America, and to a lesser extent E Asia. In S Asia and N Africa/W Asia most land with potential (and not reserved for other uses) is already used. In these regions intensification and yield increase must be the main sources of increased production. Maize, sorghum and millet are expected to show relatively greater increases in area of production since they are predominantly produced in areas with available land (SS Africa and L America), while rice and wheat will be under pressure to intensify production. Increases in sorghum and millet area may involve marginal land in semi-arid areas.

Table 31 Proportion of land with potential for agriculture already in production in developing countries in 1989/90

Source: FAO 1993; excluding China

1. Land classes as defined by FAO:

AT1 Dry semi-arid, AT2 Moist semi-arid, AT3 Sub-humid
AT4 Humid, AT5 Marginal moist semi-arid, sub-humid and humid
AT6 Naturally flooded land, AT7 Marginal naturally flooded land

2. Note that land with potential includes marginal land with some limitations to cropping.

* no, or very limited areas

Increased agricultural land use will result in increased utilization of marginal croplands (classes AT1, AT5 and AT7 in Table 31). As defined by FAO 1993, these are areas with soil, land-form or climatic constraints which limit crop yields to 20-40% of potential. In general these are least used at present (except for dry semi-arid areas where practices such as water conservation and terracing result in high proportions of land used). Marginal croplands will, however, show the most rapid increases in utilization from 1989/90 to 2010 (+15 to 20% compared to the average +12% across all land classes) as the availability of more suitable land is reduced (FAO 1993). Given the constraints on marginal land (such as slope, soil types, soil fertility etc), greater risks of land degradation may accompany this increased utilization.

Reduced grazing and forest land Increases in the areas of land used for crop production occur at the expense of other forms of land-use, mainly grazing and forests, potentially placing greater pressures on these resources and also causing changes in habitats and loss of biodiversity. However, the extent of this change needs to be put in the context of overall land-use. Land with potential for crop production (including marginal land) represents some 40% of total land in developing countries; by 2010 less than one third of this land will be cultivated (12% of total land) and increases in cropland (for all purposes) are predicted to amount to 12% of currently cropped areas (FAO 1993), say 1.5% of total land. Thus, while changes in land-use may be more significant in some countries and locations, overall reductions in grazing and forested areas will be relatively small.

Nevertheless, cropland development has been a significant component of the loss of forests, comprising up to 60% of deforestation in developing countries in recent years (World Bank 1992). Tropical forest loss currently amounts to about 0.8% per year (FAO 1983, World Resources Institute 1994), though temperate forest area is stable or expanding. (In developed countries some land is currently reverting from cropland to grazing, forest and recreational land-use). There has recently been little net change in overall grazing land availability in developing countries, though grazing land loss has been a significant component of increased pressures on grazing livestock in some areas (eg dryland areas of India). Cropland development on the most favourable niche land resources has also had significant impacts on grazing systems in some semi-arid and arid rangeland areas.

4.3.3. Impacts on soil, water and air

Soil erosion and land degradation All cultivation results in some soil loss, and depletion of soil organic matter and fertility. Excessive losses result in land degradation and abandonment which currently amounts to about 6-7 million ha per year (0.5% of the global cultivated area, El-Swaify 1991). The main causes of these losses are soil erosion and salinization in irrigated areas (the latter amounting to 1-1.5 million ha per year, FAO 1989). The risks and rates of soil erosion depend on slope, climate and soil type (including particle size, organic matter content, infiltration rates and water holding capacity). Apart from abandonment of land, soil erosion causes progressive loss of yields on most soils, requiring expensive correction and supplementation of nutrient status. In addition, off-farm impacts of lost soil through siltation and contamination of water supplies can be very high depending on the value of hydro-power and water resources affected. In the USA these losses have been estimated at over 2-3 times the direct on-farm costs (Faeth and Westra 1993). Rates of soil erosion appear to be increasing due to more intensive cultivation and mechanisation (Harris 1990). Mechanised land clearing can result in high initial rates of soil loss (eg. Thomas and Middleton 1994, in Nigeria).

Soil conservation measures can be very effective in reducing soil erosion. In the USA, practices such as contour ploughing, and more recently 'no-till' or 'minimum tillage' systems have been developed for soils at risk, together with incentives to reduce cultivation of some soils. In developing countries, low cost practices such as mulching, contour cultivation and use of grass contour bunds can reduce erosion by 40-98% and increase crop yields 6-188% (World Bank 1992, review of 200 studies). Lines of stones along contours on slight slopes in the Sahel have increased yields by 10% in average years and 50% in dry years (World Bank 1992). Suitable methods thus exist to limit soil loss, and are increasingly being applied. Greater efforts will be required to introduce conservation measures as new land is cropped, to avoid initial high rates of soil loss.

Apart from impacts on crop yields, soil erosion has significant off-site effects due to siltation, damage to downstream water storage and irrigation systems, and effects on lowland and esturine habitats.

Soil fertility Cropping inevitably depletes soil nutrients and organic matter. Continued depletion eventually results in low yields, reduced water holding capacity, and structural changes leading to greater erosion risks. Reduced yields may lead to additional clearance of new land. Nutrients and organic matter may be supplied by crop residues, composts, animal manure and crop rotations with legumes, but these sources must be supplemented with increasing use of inorganic fertilisers in order to maintain soil fertility.

Increased use of inorganic fertiliser carries the risks of losses of nutrients to the environment, particularly of nitrates and phosphates leached to groundwater or in run-off to surface water. Nitrates and phosphates contribute to eutrophication of waters (AFRC 1993), while nitrates may constitute a health hazard to humans and animals in drinking water. Cultivation of soils also results in mineralisation of some of the nitrogen held in organic matter which may then be lost as nitrates, ammonia and nitrous oxide. The latter is a potent greenhouse gas. Similarly carbon dioxide is released as organic matter is depleted.

Water Increased crop production will have impacts on both the availability and quality of water. Increases in irrigation are likely to grow to 17% of total cropland by 2010, though at a declining rate as water availability constrains development (FAO 1993). Water consumption for agriculture is currently predicted to expand by 18% between 1990-2000 (World Resources Institute 1994). Water availability and utilization for irrigation varies around the world. Asia currently uses about 54% of its stable supplies; India and China use 80% (FAO 1993). SS Africa currently uses less than 5% of its stable supplies, though these are mainly in the river basins of Central Africa. Most of North, East and Southern Africa are water deficit areas. In many areas, water utilization rates are not sustainable due to low recharge, such as around the Aral sea in Russia, in the Western USA and parts of N Africa and the M East. Depletion of water resources affects surrounding and downstream habitats and users in many locations.

Inappropriate management of irrigation has led to waterlogging and salinization of much irrigated land. Suarez (1992) estimated that up to 50% of the global irrigated area may be affected to some degree. Great potential exists to improve the efficiency of water use to reduce losses and salinization, and to increase crop yields.

Water quality is affected by contamination with soil nutrients (as described above), as well as by pesticide residues which may enter both surface and groundwater sources. Nutrient contamination causes eutrophication of both fresh and coastal waters, leading to development of algal blooms and mats, and associated toxins. Rotting algae on beaches cause noxious odours and in reservoirs can interfere with water filtration processes. The collapse of algal blooms causes anoxic conditions leading to the death of fish and other aquatic species. Maximum levels of 50 mg/l of nitrate and 5000 ug/l of phosphates are now set for drinking water in the EU, though higher levels may occur in drainage water which is subsequently diluted.

Of the pesticides, persistent herbicides such as triazine used in maize cultivation are the most important potential pollutants of water; some of these chemicals have now been banned in a number of European countries in view of the potential hazards to humans and other life (Cartwright et al 1991). In the EU, limits of 0.1 ug/l of any one chemical and 0.5 ug/l of all chemicals have been imposed.

Air Environmental impacts of cropping on air quality are derived from the direct impacts of land clearance (vegetation clearance and burning), and cultivation (loss of organic matter, production of methane, use of pesticides), but also from the indirect effects of the use of fossil fuels and other resources to support the mechanisation and supply of inputs to agriculture.

Forest land clearence is reckoned to be a significant source of long-term addition to global atmospheric carbon dioxide, thereby contributing to greenhouse gas production (CO2 emissions from other biomass burning, for example in crop residue disposal for cropland preparation, is recycled relatively rapidly into renewed plant growth and does not contribute to long-term atmospheric levels). Long-term organic matter reduction in soils will contribute only small amounts of atmospheric carbon dioxide (though has important effects on soils, Pieri 1993). Globally, deforestation contributed about 13% of anthropogenic carbon dioxide emissions in 1991 (this total including fossil fuel burning and other industrial sources, World Resources Institute 1994), mainly derived from S America, Asia and Africa with 6.1%, 3.5% and 2.5% respectively of global emissions.

Methane production from agriculture derives mainly from wet rice cultivation, contributing an estimated 29% of global anthropogenic emissions in 1991 (as defined by World Resources Institute 1994), almost entirely from Asia (27% of global emissions). None of this production is primarily for livestock feed purposes (though rice bran is an important byproduct feed in Asia).

Other more local impacts of cropping on air quality may occur, including pollution effects of land preparation and residue burning, and of pesticide residues. These have prompted controls in some developed countries.

4.3.4. Impacts on landscape and biodiversity

Landscape Changes in land-use, in the intensity of cropping, and in crop production methods (eg large scale mechanisation) can lead to changes in the type of landscape and the mosaic of land-use, vegetation types and habitats present in the environment. Such changes impact on biodiversity by altering and destroying habitats (eg forests, grasslands, hedgerows, wetlands) and affecting the numbers and mixes of biological species present. These changes can also affect the aesthetic and amenity value of the landscape which may have cultural and historical importance. Such impacts are becoming more recognised in richer developed countries and are increasingly included in land-use planning and environmental regulation.

Biodiversity Impacts on biodiversity include habitat loss and alteration due to land-use change, but also impacts of crop production practices such as pesticide-use on non-target organisms (including invertebrates, birds, animals and plants) and effects on genetic diversity of crop types grown (loss of traditional varieties and interactions with pests and diseases). Impacts on local non-target organisms can be dramatic with complete elimination of many species, including some beneficial predator species. The latter has led to the failure of pest control programmes in some cases, and hence the adoption of integrated pest management methods (IPM). A range of new approaches to pest management now exist with more limited use of chemicals in response to need, the use of resistant varieties, attractant trap technologies, biological control and anti-feedant compounds to protect crops (AFRC 1993).

Specific impacts of crop production on biodiversity, distinct from other human activities, have not been estimated. Habitat loss (due to land-use change) is considered the biggest current threat to biodiversity (World Resources Institute 1994).

4.3.5. Impacts on human health

Impacts of crop production on human health are due mainly to pollution of drinking water by nitrates and to the use of pesticides. Some disease problems are associated with the development of irrigation, such as water-borne diseases like schistosomiasis, malaria and diarrhoeal diseases (FAO 1987, von Braun 1992).

Excessive levels of nitrates in water may cause a health risk in humans, including the 'blue baby' syndrome, though the risk is low. Postulated links to cancer have not been proven (Hodge and Dunn 1992).

Pesticides may cause ill-health through contact during application, or through contamination of food. In developed countries, ill-health and deaths from exposure to chemicals during application are now rare due to control of dangerous chemicals, the provision of training and protective clothing, and regulations governing storage and disposal. These are generally lacking in developing countries where estimated poisonings range from 2 to 3.7 million per year, with about 220,000 deaths (ESCAP 1983, von Braun 1992).

Food contamination by pesticides is also now rare in developed countries, though it does occur. Maximum Residue Levels have now been established by the WHO for most chemicals in food and feedstuffs. These are monitored by regular testing in developed countries but testing methods are complex and expensive and not routinely applied in developing countries. Impacts of contamination on human health in developing countries are not documented (von Braun 1992).

4.3.6. Impacts due to the use of energy, fertilizers and pesticides in agriculture

Energy Concern has been expressed over the potential environmental impacts of the energy consumption needed to produce concentrate feeds. Energy consumption in agriculture is comprised of the direct consumption of energy on farms (for field crop operations, threshing, transport, irrigation and others) and the indirect consumption required to produce inputs for agriculture (machinery, fertilizers, pesticides). Total consumption by agriculture varies considerably between countries depending on the mix of crop and livestock production systems, and the availability and costs of land, labour, capital and energy (ranging from 0.18 GJ/ha in Australia to 5.0, 19.5, 55.1 and 74.0 GJ/ha in USA, UK, Japan and The Netherlands respectively, and 4.8 to 24.0 GJ/ha in Pakistan and China, see Stout 1990). Consumption is generally higher per ha of cropland (though not necessarily per unit of yield) in developed than in developing countries (as input levels increase to raise outputs and to substitute for land and human labour, see Table 32 below).

Energy consumption by agriculture to the farm gate is generally a relatively low proportion of total national energy consumption (ranging from 2-3% in developed to 5-6% in developing countries, Stout 1990). (Energy consumption for food transport, processing and preparation may amount to a further 2-3 % in developed and 15-20% of total energy consumption in developing countries, Stout 1990). Given that crop production consumes only part of the energy devoted to agriculture (say two thirds), and that crop production for feeds (coarse grains, wheat and roots and tubers) constitutes only 21% of global cropland use, energy consumption for the production of livestock feeds may thus be crudely estimated at less than 0.4% of total energy consumption.

Table 32 Energy inputs to crop production under different production systems

1. Chancellor 1978, in Sout 1990 - use of 'commercial' fossil fuel energy resources only; traditional maize production subsistence system in Mexico.

2. Myers 1983, in Stout 1990 - wheat production in Tunisia at two levels of mechanisation, other inputs and yields (low and intermediate)

3. Bonny 1993 - high input wheat production in in France 1990, not counting human labour inputs

4. Pimentel 1991 - high input maize in USA 1990

5. Other energy requirements including drying and irrigation

Energy requirements for the different inputs to cropping are summarised for some examples in Table 32. (Note that the examples are not all directly comparable, being derived from different sources with differing definitions). In high input systems, indirect energy requirements for machinery, fertilizers and pesticides account for 11-12%, 35-57% and 6-10% respectively of total energy requirements. The majority of fertilizer inputs are due to nitrogen fertilizer manufacture.

Energy inputs for feed crops in UK (not shown in Table 32) have been estimated at 18.9 and 15.7 GJ/ha (4.9 and 4.4 GJ/t) for wheat and barley (Leach 1976). Inputs for maize production were also estimated for six developing countries by Leach, ranging from 0.96 to 4.06 GJ/ha due to lower mechanisation and fertilizer inputs. Estimates for developing regions over the period 1980-2000 (overall crops) are shown in Table 33 (after FAO 1979).

Table 33 Estimated use of energy for agriculture in developing countries 1980 to 2000

Source: FAO 1979

Energy consumption per ha of cropland is predicted to more than treble in most developing regions over the period 1988 to 2000, though generally remaining under a third of the levels in developed regions. Increased energy use will be mainly due to mechanisation and fertilizers.

Energy sources for agriculture include both commercial sources (fossil fuels, nuclear power and electricity), and traditional sources (renewable biomass, including fuel wood, crop wastes and animal dung, and animal draught power and human labour). In developed countries, traditional energy sources have been almost completely replaced, while in many developing countries they still constitute over 50% of total energy supplies (and over 90% in poorer countries) (see Stout 1990, World Resources Institute 1994). The various sources of energy exert differing impacts on the environment; the effects of changes in energy consumption for agriculture will have a series of complex implications for environments, with both negative and positive consequences (such as reduced draught animal grazing with increased mechanisation, increased manure availability for cropping with increased household fuel supplies, improved crop and land husbandry in higher input cropping systems with fertilizers) in addition to potential greenhouse gas effects.

Fertilizers Application rates of fertilizers over the period 1975/77 to 1990/92 are reviewed in Table 34 (illustrating total nutrient applications). Rates are generally highest in developed regions, particularly in W Europe, but have increased rapidly in developing regions in recent years while stabilising or declining in developed regions. Very high rates of application are now used in some E Asian countries with high intensity land-use (eg Japan and Korea with 402 and 440 kg/ha cropland respectively in 1989/91, World Resources Institute). Consumption has more than doubled in many developing countries in Asia over the last 10 years (eg 33 to 73kg/ha in India and 144 to 284 kg/ha in China). Consumption remains especially low in SS Africa and has not increased notably in recent years compared to other developing regions.

Table 34 Use of fertilizers by regions of the world 1975/77 to 1990/92

Source: FAO SOFA database; fertilizer accounted as weights of nutrients supplied including nitrogen, phosphate (P2O5) and potash (K2O) supplied; average annual consumption calculated over three year periods, 1975-77, 1985-87 and 1990-92

Environmental impacts of fertilizer application are mainly the effects of nutrient leaching and run-off to contaminate water ways and aquatic ecosystems, including eutrophication. However, these effects are not always found, depending on soil types, crop nutrient demands and husbandry factors such as timing of applications. Provision of fertilizer nutrients also has beneficial impacts on correction and maintenance of soil fertility and other soil conditions when well managed.

Other environmental impacts include the energy costs and impacts of fertilizer production, estimated at 20-70% of the total energy costs of agriculture depending on production systems. At a crude average of 50% of total energy use, fertilizer production may be estimated to constitute 1-1.5% of global energy consumption, with some 21% only of this devoted to production of crops solely for feed.

Pesticides Pesticide use has grown over the last 40 years as part of the green revolution first in the developed countries and latterly in the developing. Developed countries still consume most pesticides; in 1993 N America consumed 30%, W Europe 24%, E Europe 4%, E Asia (chiefly Japan and China) 27%, Latin America 10% and the rest of the world 5% (BAA 1993). In the same year, pesticide use comprised 46% herbicides, 30% insecticides, 19% fungicides and 5% others. Average application rates over all pesticides are not generally available (or meaningful in view of differences in pesticide types and active ingredient contents); FAO data for 1989 reviewed by World Resources Institute 1994 suggest rates of 3.1 kg/ha in Germany, and 11.8, 4.9 and 1.4 kg/ha in developed countries of Belgium, Hungary and Poland respectively and 6.4, 3.6, 1.5, 1.6 and 0.4 kg/ha in Egypt, Colombia, Zimbabwe, Thailand and Cameroon. Other estimates suggest application rates of about 2.3, 10 and 0.5 kg/ha in USA, Japan and India (Pesticide News 1994). Rates of application have recently stabilised or declined in developed countries but are still increasing rapidly in developing countries.

The crops receiving the highest applications of pesticides include rice (14% of the total in 1993), cotton (11%), maize (11%), soyabean (8%) and cereals (especially wheat, 14%) (BAA 1994). Though all of these crops provide concentrate feeds, only maize includes substantial areas grown solely for feeds. Direct benefits of pesticide use have been estimated to be in the range of US$ 3-5 per dollar invested

Environmental impacts of pesticides include impacts on non-target organisms, both beneficial insects (such as bees and pest predators) and soil organisms, damage to water ecosystems and contamination of water resources (eg by atrazine herbicide), and feed chain accumulation effects in mammals, birds and man, apart from other impacts on human health as outlined in Section 4.3.5. above. Estimation of environmental impacts and costs is complex, requiring detailed field research; estimates of annual costs in the USA have ranged from US$ 2.2-8.0 billion, with additional costs of US$1.2 billion for groundwater monitoring (Pimentel et al 1993)

4.4. Environmental impacts of feed commodity production and mitigation measures (some examples).

The following sections describe the environmental impacts of the production of some of the major feed commodities, and approaches to reduction and mitigation of some of these effects.

The crops providing the bulk of concentrate feeds for livestock include maize, barley, and wheat cereals and soyabean, cotton seed, rapeseed and sunflower oilseeds. Sorghum and groundnut are of lesser global importance but may be significant locally. Cassava and sweet potato are mainly grown for food; only a small proportion of global production is for livestock feed, though there is potential for this to be increased.

4.4.1. Wheat and barley production in Northern Europe

Cereal cropping in N Europe is dominated by wheat and barley, much of which is grown for livestock feed. In the UK in 1992 wheat and barley accounted for 42% and 26% of cropped area respectively, with 43% and 62% respectively utilized for feed. Much of the rest of the barley was used for brewing and distilling, with residues fed to livestock (MAFF 1993).

Environmental impacts of wheat and barley production have included the expansion of cropping into formerly uncropped areas, such as former upland grazing lands and lowland permanent grasslands and marshlands, as well as removal of hedgerows and small woodlands. An estimated reduction of 25% of hedgerows and 87% of farmland trees occurred in the 25 years to the mid 1980s (Bowers and Cheshire 1984). Intensification of cropping has resulted in increased use of pesticides (including herbicides, insecticides, fungicides, molluscicides and plant growth regulators), with impacts on both pests and non-target wildlife, and on human health. Increased use of fertilisers has resulted in nutrient loss and contamination of ground and surface water through leaching and run-off.

Impacts on wildlife have included reductions in several bird species. Thus, in UK grey partridge numbers declined from 25 to 5 pairs/km2 from 1952 to the mid 1980s (Sotherton 1992) due to reductions in insect food supply caused by removal of insect weed habitats in hedgerows and headlands. Raptor species were severely depleted by the use of pesticides, while hedge nesting species were reduced by loss of habitat as well as of food (Bowers and Cheshire 1984).

The extent of the impacts of pesticide use have recently been examined in longterm trials of different application strategies. The Boxworth Project in UK tested standard practice of full insurance spraying against spraying in relation to thresholds of monitored weed, pest and disease problems or integrated programmes using resistant varieties and more specific pesticides (HMSO 1992). The greatest impact of pesticide use was on invertebrates, with virtually complete elimination under full insurance spraying, including many potentially beneficial non-target species. Under less intensive spraying regimes more beneficial species survived and longterm impacts on birds and small mammals may be reduced (Ciligi et al 1993).

Similar observations have been made in other European countries (El Titti 1992). Various approaches to reduced pesticide application are now under development, including Integrated Farming Systems (IFS, El Titti 1992), Less Intensive Farming and the Environment (LIFE, AFRC 1992) and IPM methods. Reduced chemical and fertilizer usage, and minimum tillage practices in these systems result in reduced environmental impacts and greater financial gross margins through lowered costs, though yields may also be slightly reduced. Policy interventions to limit input use and environmental impacts are increasingly being adopted in European agriculture. These include the set-aside programme in EU, and policies in other countries to tax fertilisers and pesticides, and to control pesticide residues and nitrate losses from agricultural land, as well as programmes to preserve habitats and landscapes (OECD 1993).

4.4.2. Maize production in the USA

Maize production in the USA has developed through three main phases of, firstly, area expansion (from 1900 to 1930), followed by yield increase through hybrid breeding (1930-mid 1950s), and yield increases through intensification of inputs to the mid-1980s. Improved maize yields require careful control of weeds and insect pests, and modern varieties respond to high levels of fertilizer application. Recently environmental and cost pressures have encouraged the development of lower, more efficient, input systems with maintained yields (Byerlee and Lopez-Pereira, 1994). As in Europe, these sources of increased production have had different environmental consequences. Of particular concern in the USA have been the effects on soil erosion and the impacts of fertilizers and pesticides on the environment.

Between 1933 and 1937, the combined effects of drought and cultivation of marginal soils resulted in severe wind erosion damage to about 3 million ha. Soil conservation activities have resulted in reduced rates of erosion but soil loss is still a problem for both agricultural and off-site effects (siltation and erosion) (Soule et al 1990). Conservation tillage, including contour cultivation and minimum tillage methods are now adopted over about 30% of the rainfed maize area, but only recently in irrigated areas. Under 1985 legislation, highly erodible land has been identified and incentives provided to take it out of production, though studies by Faeth and Westra (1993) suggest that the USA agricultural support system still does not provide sufficient incentives to resource-conserving production systems.

Maize accounts for 53% of pesticide usage in the USA. The major impacts of pesticide use are in losses of non-target invertebrates, crop losses, effects on domestic livestock, fisheries losses, water contamination and public health effects. Persistent herbicides such as atrazine are particular problems in maize, and have been leached to groundwater at above the 3 ppb Health Advisory Level in some instances (eg. Spalding et al 1989).

Nitrate and phosphate contamination of surface and groundwater are of concern in intensive arable areas. Leaching is greatest on shallow soils with a high water table, while surface run-off is greatest in areas prone to soil erosion. Much of the problem is due to over-application of fertilizers (eg. Schepers et al 1991).

Much research effort is now devoted to the development of low input cropping systems, such as the Low Input/Sustainable Agriculture (LISA) programme (O'Connell 1992). Under these programmes, alternative pesticide and fertilizer application strategies may be combined with pest attractant and biological control methods, crop rotations and resistant varieties as appropriate.

Additional research programmes are underway, for example to develop herbicide resistant maize so that non-persistent herbicides can be used in the crop (Hayenga et al 1992), and to develop models to define herbicide application strategies that limit groundwater contamination (Hoag and Hornsby 1992). Similarly, modelling of irrigation and drainage systems has demonstrated coincidental agricultural and environmental benefits of improved irrigation management and reduced leaching losses.(Miller et al 1993). Modelling of different crop production strategies and nutrient losses has shown that combinations of methods are available which can satisfy both agricultural and environmental objectives (Foltz et al 1991).

4.4.3. Soya bean production in Brazil, Asia and Africa

Soya bean production is less dependant on inputs than is maize. As a legume it fixes nitrogen so requires less nitrogen fertilizer, though it does need phosphates. Soya bean is sensitive to weeds in the early stages of establishment, so herbicides are routinely used in large scale production. Utilization of insecticides and fungicides is less than for maize. The risks of soil erosion are moderately high until the crop canopy has developed. Overall, however, the environmental impacts of soya bean cultivation are less than for maize.

Brazil is the second largest producer of soya bean after the USA and production has increased rapidly since the 1960s. Much of the crop is grown under similar systems to those of the USA. Most of the increased production up to 1989 has come from increased area planted (90%), and only 10% from yield improvement. Increase of crop areas occurred mainly in Parana and Rio Grande do Sol states, under large scale production. Production of some staple food crops declined (Soskin 1988). Input utilization is lower than in the USA, but not so carefully targeted or controlled. Recent increases in yield suggest some intensification of production.

Environmental impacts have included changes in land-use, including clearing of forest. Environmental impacts of production, through application of pesticides and fertilizers have probably also occurred but these are not documented.

Expansion of soya bean production has also occurred in India, mainly under rainfed conditions in Madhya Pradesh. The increase has been due to increased area of crop, generally through replacement of other crops rather than development of new land. Yields are low at 1t/ha, partly because of low inputs, though potential exists for rapid increase (Tiwari and Bhatnagar 1992). Introduction of the crop has increased farm incomes, bringing socio-economic benefits and no reported negative environmental impacts (Rao 1992).

Scope exists to introduce soya bean to the wheat-rice rotation crop areas of northern India. Throughout much of this area, and in Pakistan and Nepal, wheat and rice yields are not as high as expected; the introduction of a legume could have beneficial effects on productivity and reduce input requirements (Sidhu and Sidhu 1991). Similarly in Indonesia, soya bean has proved a profitable crop for adoption in intensive cropping systems by small-holder farmers on Java (Randot and Lancon 1992).

In Africa, soya bean production has been increasing in Nigeria, Cote d'Ivoire, Ghana, Zambia and Zimbabwe. In Nigeria, the crop has fitted well in some farming systems, requiring less labour and fertilizer than other crops. It has been grown inter-cropped with sorghum, which it benefits by providing nitrogen and suppressing weeds.

4.4.4. Cassava production in Thailand

Cassava is produced mainly for direct food consumption and some starch and alcohol production. Feed-use comprises some 5% of production. Production for feed is concentrated in SE and E Asia, particularly Thailand, China and Indonesia. Cassava can be grown in a wide range of soils and climates. It is well adapted to acidic, low fertility soils and can be grown with little land preparation or inputs. However, under these conditions, the crop can deplete soil fertility and cause soil erosion. The crop is often grown inter-cropped, or sparsely planted in fallows without land preparation. In general, the environmental impacts of production are less than for cereals.

A rapid increase in production in Thailand occurred through opening-up of new lands in the north-east following road construction into the area in the 1970s. In Thailand the crop is grown as a sole crop on hillsides too steep for rice and not suitable for other crops. Longterm production without fertilizers resulted in depletion of soil nutrients, particularly potassium, though this could be fully restored by fertilizer application (Howeler 1991).

Soil erosion under cassava is generally less than under other crops. Since the crop is in place for about 18 months, exposure and cultivation of soil is reduced compared to annual crops. Howeler (1991) reported soil losses of 6.3 t/ha under cassava compared to 44 t/ha under beans using the same land preparation method. Soils losses can be reduced by minimum tillage, mulching and fertilizer application to ensure rapid canopy development, though few farmers yet adopt these methods (Harper and El-Swaify 1988).

Cassava does not require high levels of other inputs. It is sensitive to weed competition in early stages of growth. Under sole cropping systems herbicides are used, while under mixed cropping hand weeding is more usual. The crop is generally thought of as tolerant of pests and diseases so pesticides are not usually applied. In Africa, cassava mealy bug and cassava green mite are serious problems, but biological control methods have reduced the need for pesticides, with environmental benefits (Moreno 1992).

The production of cassava in NE Thailand has generally been financially beneficial to the estimated 2.5 million people who take part in its production (Smit 1988).

4.4.5. Barley production in the Middle East

Barley production for feed has increased dramatically in the Middle East over the last 30 years. In Syria, the area of production increased from 750,000 ha in 1961/63 to 2.9 million ha by 1988/89. Similar expansion has occurred in Jordan and Iraq. The main reason for expansion has been the huge increase in demand for sheep meat with rising incomes from oil revenues, and support to rural shepherding populations through subsidisation of barley prices. In Syria, the sheep flock increased from 3.1 million to 13.3 million over the same period (Cooper and Bailey 1991).

Both the expansion of sheep numbers and barley cropped areas have had environmental implications. Increased barley cultivation has resulted in expansion into more marginal croplands, with the result of more variable and lower yields. Environmental impacts are not well documented but are thought to include increased soil loss through erosion and depletion of soil fertility and organic matter. The sustainability of cropping in some areas is in doubt, though research results from the region suggest that improved cropping systems and husbandry could stabilise yields and reduce the threat to fragile lands (Cooper and Bailey 1991).

4.5. Summary of environmental impacts of production of feed crop commodities

The assessment of environmental impacts of production of feed crops is limited by three main factors. First, there is a general lack of data or case study material describing the specific environmental impacts of many of the crops. Secondly, the impacts actually engendered vary depending on the context of production of the particular crop, including soil and climate conditions, current intensity of land-use and occurrence of land-use changes, crop mixtures and rotations, and the production technologies and inputs employed. Thirdly many impacts occur outside the production systems in which they are created, as off-site, downstream or external impacts; these are frequently difficult to trace and measure. No general quantitative assessment of the environmnetal impacts of feed crop production is thus possible, and no attribution to farming or livestock production system zones.

An additional difficulty concerns the apportioning of impacts to feed crop production. Many crops serve multiple purposes, with variable proportions utilized as feed in different circumstances.

An attempt is made below to summarise some of the major types and sources of environmental impacts due to changes in cropping patterns and to individual crops contributing most to concentrate feed supplies. Changes in land-use, cropped areas, cropping intensity and crop yields potentially exert different kinds of pressures on the environment, both positive and negative. These are summarised in Table 35. Thus, increases in cropped areas are associated with changes in land-use as well as exposing new (including some marginal) lands to cultivation and consequent soil loss. Increased cropping intensity results in reduced fallows in some circumstances, or more frequent and intensive cultivation of soils, or use of irrigation water. Increased crop yields usually imply increased application of inputs, with risks of pollution and implications of greater energy demands in agriculture.

The occurrence and effects of these impacts varies between particular locations. Negative impacts do not always occur, depending on the management of crop production and soils.

Table 35 Potential environmental implications of different sources of increased crop production

Under good land management, and for most crops, improvement or maintenance in soil conditions may be achieved. In different circumstances, the prospect of increased outputs, or the lack of alternatives, may result in investment in practices such as terracing or other soil conservation measures, water harvesting, storage and drainage, and in farm forestation, crop rotation, tillage or fertilization practices that enhance resources and the farming environment.

Individual crops exert somewhat different impacts on the environment. Table 36 indicates the likely relative contributions of individual crops to the major sources of environmental impact on soils and water under current typical production practices. Thus, environmental impacts may be derived from erosion and soil nutrient losses due to cropping practices, leaching and run-off, including the losses from usually practiced fertilizer regimes. Crops differ in their demands for and use of soil moisture and water resources; soil moisture depletion may be a factor in predisposing soils to nutrient loss and degradation by erosion. Crops also differ in their relative demands on soil nutrients, and therefore the likely depletion of soil fertility.

Table 36 Relative contribution to sources of environmental impacts on soils and water of different crops providing livestock feed

1. +, ++ and +++ indicating low, moderate or high potential impact

The cereal crops in general have the potential to cause greater environmental impacts than other crops, particularly maize. Potential impacts of maize are due to heavy fertilizer and pesticide use, and high water demand. Potential impacts are generally lowest for the legume crops, soya bean and the pulses. Comparative erosion risks are marginally greater from maize, sorghum and soya bean, in part because of the kinds of soils and climates they may be grown in and because of the patterns of establishment of their plant canopies, and usual cultivation practices. Risks of pollution due to nitrate and phosphate loss are greatest from maize and wheat, while risks of soil nutrient depletion are greatest in cassava and sweet potato.

Additional references

Stout B A (1990) Handbook of Energy for World Agriculture. Elsevier Applied Science, London and New York

Pimentel D (1991) Energy Inputs in Production Agriculture. In R M Peart (Ed) Analysis of Agricultural Energy Systems: Energy in World Agriculture. Elsevier, Amsterdam

Bonny S (1993) Is agriculture using more and more energy? A French case study. Agricultural Systems, 43, 51-66

BAA (1994) The Agrochemical Industry; The World Market in 1993. BAA Annual Review and Handbook 1994, British Agrochemicals Association, UK

Cheeke P R (1993) Impacts of Livestock Production on Society, Diet/Health and the Environment. Interstate Publishers Inc, Danville, Illinois.

World Resources Institute (1994) World Resources 1994-95. The World Resources Institute, Oxford University Press, New York and Oxford.

Pieri C (1993) Soil Fertility Management for Intensive Agriculture in the Humid Tropics. In J P Srivastava and H Alderman (Eds) Agriculture and Environmental Challenges. Proceedings of the Thirteenth Agriculture Sector Symposium. The World Bank, Washington