Environmental Science & Policy 8 (2005) 439–451 www.elsevier.com/locate/envsciNutrient flows in international trade: Ecology and policy issues Ulrike Grote *, Eric Craswell 1, Paul Vlek Center for Development Research (ZEF), University of Bonn, Walter-Flex Str. 3, 53113 Bonn, Germany Available online 2 September 2005Abstract Impacts of increasing population pressure on food demand and land resources has sparked interest in nutrient balances and flows at a range of scales. West Asia/North Africa, China, and sub-Saharan Africa are net importers of NPK in agricultural commodities. These imported nutrients do not, however, redress the widely recognized declines in fertility in sub-Saharan African soils, because the nutrients imported are commonly concentrated in the cities, creating waste disposal problems rather than alleviating deficiencies in rural soils. Countries with a net loss of NPK in agricultural commodities are the major food exporting countries—the United States, Australia, and some Latin American countries. In the case of the United States, exports of NPK will increase from 3.1 Tg in 1997 to 4.8 Tg in 2020. The results suggest that between 1997 and 2020, total international net flows of NPK in traded agricultural commodities will double to 8.8 million tonnes. Against this background, the paper analyses the impact of different policy measures on nutrient flows and balances. This includes not only the effects of agricultural trade liberalization and the reduction of subsidies, but also the more direct environmental policies like nutrient accounting schemes, eco-labeling, and nutrient trading. It finally stresses the need for environmental costs to be factored into the debate on nutrient management and advocates more inter-disciplinary research on these important problems. # 2005 Elsevier Ltd. All rights reserved. Keywords: Nutrient flows; International trade; Nutrient trading permits; Nutrient accounting schemes; Environmental degradation1. Introduction Human-induced changes to the cycling of nutrients in terrestrial ecosystems significantly affect the sustainability of food production, the state of the natural resource base, and the health of the environment. Agricultural expansion and intensification to meet the needs of the expanding population have amplified human dominance of the Earth’s ecosystems to the point where between one-third and onehalf of the land surface has been transformed (Vitousek et al., 1997). Moreover, Smil (2001) credits the synthesis of ammonia through the Haber–Bosch process as the most important technical invention of the 20th century—without fertilizer nitrogen the earth could not sustain 6 billion people. The changes wrought by humans in nutrient cycling and budgets are complex and vary widely in magnitude across * Corresponding author. E-mail address: [email protected] (U. Grote). 1 Present address: Global Water System Project, Walter-Flex Str. 3, 53113 Bonn, Germany. 1462-9011/$ – see front matter # 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envsci.2005.05.001the globe. Vlek et al. (1997) estimate that 230 million tonnes2 (230 Tg) of plant nutrients are removed yearly from agricultural soils, whereas global fertilizer consumption of N, P2O5 and K2O is 130 Tg. In the case of nitrogen the fertilizer supplements are augmented by an estimated 90 Tg from biological fixation. Although developing countries now consume half the global fertilizer production, much is used on cereal crops grown on the irrigated lands of Asia or on cash crops. Large rainfed areas producing food crops in the tropics, particularly in sub-Saharan Africa, receive little or no fertilizer. Low inputs and limited re-cycling of nutrients by poor smallholders in these areas lead to negative nutrient balances that render continued crop production unsustainable (Stoorvogel and Smaling, 1990). This exploitation of native soil fertility is coupled to a 2 This paper utilises SI units as follows: Mg = 1000 kg (1 metric tonne); Gg = 1,000,000 kg (1000 tonne); Tg = 1,000,000,000 kg (or 1 million tonne). Unless specified as the oxide forms P2O5 or K2O, amounts of P and K are converted to, and expressed as uncombined elements; the exceptions are where quoted papers expressed combined NPK data in oxide forms that could not be converted to elemental forms.440U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451decline in soil organic matter that contributes carbon dioxide to climate change. The negative nutrient balances in agricultural lands due to inadequate use of external inputs, and the inequitable distribution of nutrients between and within countries, may be exacerbated by the transport of nutrients in harvested products. At the global scale, Miwa (1992) showed that international trade in food commodities led to significant negative balances in exporting countries and accumulations in importing countries. Japanese scientists recognized the importance of this problem in their own country, which as a major food and feed grain importer, faces serious nutrient disposal problems due to pollution and eutrophication. Miwa (1992) emphasized that each country should consider the effects on its ecosystems of nutrient imports. He pointed to the increasing demand for livestock products in developing countries and the expansion of feed grain use. Livestock production lies at the heart of environmental concerns because, as indicated by data for nitrogen, the average efficiency of nutrient conversion from feed to animal products is only 10%, although on efficient dairy farms the range is 15–25% (van der Hoek, 1998). The environmental impacts of inter- and intra-national nutrient flows are commonly concentrated in the burgeoning cities. For example, Faerge et al. (2001) estimated that 20,000 Mg of nutrients were annually imported in food into Bangkok, and that large amounts of nutrients were lost, mainly to the waterways. Coping with high concentrations of nutrients in the environment is a major problem facing urban administrations, and the problems are likely to get worse with the continued trend to urbanization. Similar problems occur in intensive animal production systems. Nutrients can be re-cycled through the application of wastes to crops and forages but, in spite of the obvious benefits, the extent of re-cycling is limited in most cities. Income growth and expanded demand for animal products in developing countries will increase inter- and intra-national trade in animal feed, aggravating the mining of rural soils and the environmental problems in animal production areas. Environmental impacts on waterways of nutrient outflows from agricultural lands are widespread. In marginal areas, erosion of upper-catchment soil by water (and in some cases by wind) enriches surface waters with nutrients. Sediment is deposited and enriches lowland areas. However, annual net ocean outflows of sediments in Asia are as high as 7500 Tg, representing a major loss of nutrients to the countries concerned (Milliman and Meade, 1983). Global net outflows of dissolved inorganic nitrogen to the oceans have been estimated at 18,291 Tg (Seitzinger and Kroeze, 1998). These flows of nutrients are in turn affected by human diversions of surface water, such as dams that collect silt and reduce flows to natural wetlands. Other environmentally important human-induced perturbations of nutrient cycles include impacts on fluxes of nitrousoxide that contribute to the greenhouse effect and ozone depletion and the accumulation in groundwater of nitrates and other nutrients that affect human health. Nitrogen has been more extensively studied than the other macronutrients, phosphorus and potassium, possibly because human impacts on the global nitrogen cycle extend to industrial perturbations, and atmospheric as well as terrestrial and aquatic phases (Galloway and Cowling, 2002). The above overview indicates that a substantial, though fragmented knowledge base is developing on the agricultural, ecological, and environmental aspects of alterations to nutrient flows and balances at different scales. The information and data vary in accuracy and are derived from a dispersed group of studies by authors from a wide range of disciplinary interests, including ecologists, soil scientists, and agricultural scientists. In contrast, the economic impacts and implications of these perturbations to nutrient cycling have been relatively neglected. One of the exceptions in the area of nutrient balances is the work of Drechsel and Gyiele (1999) who developed a framework for the economic assessment of soil nutrient depletion. Their data show that the cost of replacing nutrients lost from arable land in countries of sub-Saharan Africa ranges from <1% to as high as 25% of the national agricultural gross domestic product. Related to the population engaged in agriculture, every farm member contributes about US$ 32 to the annual nutrient deficit. Related to the annual and permanent cropland in subSaharan Africa, the average costs are about US$ 20/ha and per year. At the other end of the scale, combating environmental pollution from imported nutrients in urban areas is a major multi-billion dollar industry in both developing and developed countries. This paper focuses on two inter-related aspects of nutrient flows. We present estimates of nutrient flows in internationally traded agricultural commodities in 1997 and IFPRI projections to 2020, and discuss the associated equity issues and environmental consequences. We then consider the implications of current and possible agricultural, trade and environmental policies for nutrient flows and balances associated with international trade.2. Nutrient flows in agricultural trade 2.1. Methods We followed the study of Miwa (1992) who utilized FAO data on food production and trade in the period 1979–1981, calculating nutrient flows using average nutrient contents of the commodities. In the IFPRI IMPACT study ‘‘Global Food Projections to 2020’’ by Rosegrant et al. (2001), future nutrient flows in traded agricultural commodities, using FAO data from 1997 as a baseline, have been projected. The IMPACT projections of supply and demand for major agricultural commodities are integrated with price and subsidy information to derive net trade by commodity forU. Grote et al. / Environmental Science & Policy 8 (2005) 439–451each country. The data include neither non-food commodities such as wool and cotton, nor industrial commodities such as rubber. IFPRI provided data for the commodities listed in Appendix I. This appendix also shows the nitrogen, phosphorus and potassium contents of the commodities; the data were taken from a variety of sources, as also listed, and these can be considered as average values. Appropriate corrections were made for the moisture content where analytical data were on a dry weight basis. Note that nutrient data are expressed in elemental rather than oxide forms; the use of P and K oxide data is normally restricted to use with fertilizer statistics. In order to make the data equivalent, fertilizer data used for comparisons with nutrient flows in net trade were converted from oxide to elemental contents. The countries and regional groupings in the IFPRI data used in the present study can be seen at Rosegrant et al. (2001). The presentation of the nutrient data and manipulations of the data also requires some comment. In trade data, an export is normally expressed as a positive and imports as negative. However, in the case of nutrient balances, the export becomes a negative and an import gain to the country. The signs on the IFPRI data converted to nutrient flows were therefore changed to reflect the ecological implications. Additionally, the IFPRI data on net trade are presented as individual or groups of like commodities (e.g. roots and tubers) because quantities of commodities such as eggs and wheat are not additive. In the case of nutrients, the weights of N, P and K in different commodities are additive, and amounts of the different nutrients can also be summed. We were therefore able to aggregate the nutrient data and summarize them as shown in Appendix II, which also shows441fertilizer consumption data on NPK expressed as the elemental forms so that comparisons can be made with the nutrient trade data. 2.2. Results on nutrient flows in agricultural trade The 2020 study by Rosegrant et al. (2001) provides a wealth of insights into major changes between 1997 and 2020 in the supply and demand for major food commodities in countries from developed and developing regions. Under their baseline scenario, economic growth, rising incomes and rapid urbanization in developing countries are driving fundamental changes in the global structure of food demand. As incomes rise, direct consumption of maize and coarse grain will shift to wheat and rice, while the higher demand for meat will increase the demand for feed grain. Agricultural trade will increase, with wheat leading the cereals and poultry the livestock commodities. West Asia/ North Africa (WANA), China and sub-Saharan Africa will increase imports, whereas the United States, Latin America and Southeast Asia will increase the value of their net exports. For a detailed analysis of the IMPACT data, readers are referred to the IFPRI publication (Rosegrant et al., 2001). Aggregated data on net flows of NPK in trade vary widely across regions and countries (Fig. 1). Note that this aggregation of the data does not provide insights into intra-regional trade. The countries and regions showing major gains of NPK through imports of traded commodities are WANA and China. Both show major increases between 1997 and 2020, and this is especially true in China, which will increase NPK imported in agricultural commoditiesFig. 1. Relative flows of N, P, K in net agricultural trade 1997 and 2020 (IMPACT model).442U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451from 0.6 to 2.2 Tg. These imports will probably go to the cities where, as noted above, major nutrient excesses are causing serious water pollution. Other countries and regions with moderate levels of NPK in imports are EC15, Japan, Southeast Asia and sub-Saharan Africa. From a balance in 1997, South Asia is predicted to become a net importer of NPK in food (0.6 Tg). The NPK imported in food into subSaharan Africa is predicted to increase significantly between 1997 and 2020, as is the case with other developing regions such as Southeast Asia. Fig. 1 also shows that the United States, Australia, Latin America, and ‘other developed regions’ (includes Canada), which represent the major food exporting countries, also show the largest net loss of NPK in agricultural commodity trade. In the case of the United States, the exports of NPK will increase from 3.1 Tg in 1997 to 4.8 Tg in 2020. This represents a major flow of nutrients in terms of the potential perturbation of nutrient cycles in natural ecosystems. The most significant increase in NPK outflows is Latin America, which loses 0.65 Tg in 1997 increasing to 1.95 Tg in 2020. Eastern Europe is predicted to increase exports of nutrients to 0.2 Tg, from a low level of import (0.15 Tg) in 1997. The net trade in NPK in the former Soviet Union is generally close to zero in both years. Putting the data on nutrient flows in traded agricultural commodities into perspective requires a basis for comparison. Some researchers such as Miwa (1992) have expressed country data as kg/ha of agricultural land. This comparison indicates the potential to recycle nutrients by spreadinglivestock and urban wastes. However, this approach may be misleading since the practicality of spreading nutrients imported into cities across distant arable areas is questionable. Furthermore, areas importing feed for livestock may be distant from the bulk of arable land, making the spreading of nutrients across all cropping land impractical. An alternative basis for comparison is the fertilizer consumption in the importing or exporting country concerned. This comparison does not take account of the fact that traded commodities contain non-fertilizer derived nutrients such as nitrogen from biological fixation; fixed N is especially important in traded legumes such as soybean. Nevertheless, as shown in Fig. 2, the data on NPK in net trade in 1997 were calculated as a percentage of fertilizer consumption in the corresponding country or region. Data on projected fertilizer consumption in 2020 were not available. The comparisons with fertilizer consumption in Fig. 2 provide useful insights into the relative importance of the nutrient trade flows. The largest exporter of nutrients, the United States, exported in 1997 only the equivalent of 18% of its fertilizer consumption. Nevertheless, the large amounts of nutrients involved do present challenges to US policymakers in the areas of subsidies, trade and environmental protection. The largest importer of nutrients in absolute terms is China, but the amounts of NPK represent only 2% of fertilizer consumption in 1997. Clearly domestic NPK consumption in China dwarfs the NPK imports in food. On the other hand, the concentration of importedFig. 2. Net flows of N, P, K in trade in 1997 expressed as a percentage of fertilizer consumption.U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451nutrients in the cities may still be a cause of concern since environmental problems are already serious, as noted in the discussion above. Japanese imports of the equivalent of 88 to 101% of fertilizer consumption point to the familiar problem of nutrient overload, as discussed above. Although the aggregated data presented for the EC15 do not reveal it, the Netherlands, Belgium and other small countries that import large amounts of animal feeds have the same environmental problems. In 1997, sub-Saharan Africa imported the equivalent of 26% of fertilizer consumption. At first sight this result may appear to be a positive trend, since the major problem in subSaharan Africa is nutrient depletion in rural areas due to low rates of fertilizer use. However, the data presented are averages across and within countries. If the nutrients imported in food end up as wastes in the major cities, the rural lands will not benefit. The result does highlight the potential for nutrient re-cycling in peri-urban and urban agriculture. Another key issue is that while the fertilizer data include nutrients applied to plantation crops, the trade data exclude plantation and industrial crops. Vlek (1993) estimated that in 1987 the export of N, P2O5 and K2O in agricultural commodities, mainly cotton, tobacco, sugar, coffee, cocoa and tea, was 296 tonnes . In WANA the import of NPK in food is equivalent to 26% of fertilizer con sumption. On the debit side, exports of nutrients from Latin America were 7% of fertilizer use in 1997. Interpretation of these data indicate an exaggerated effect when the exports of soybean contain biologically fixed rather than fertilizer N. Latin American countries will need to increase fertilizer use to avert soil fertility decline. Similar comments apply to Australia, which is exporting large amounts of NPK in relation to fertilizer consumption. In Australia’s case the biologically fixed nitrogen comes from pasture legumes443grown in rotation with cereal crops. Nevertheless, the significant increases in exports to 2020 also point to the need to maintain soil fertility by replacing exported nutrients. The separation of the nutrients N, P and K in the net trade data is shown in Fig. 3. The results show the proportional dominance of N in the nutrient movements. Potassium transfers are nevertheless significant and may contribute opportunities for eventual re-cycling of this important nutrient, given its high cost of mining and transportation. Nitrogen is the most dynamic nutrient and after transformation can move in the atmosphere as well as aquatic systems. Nitrogen has been the most studied nutrient and is the subject of regular international conferences (see Galloway and Cowling, 2002). The amounts of N involved in transfers through trade are significant ecologically, especially when our 2020 projections are considered. Most importantly, as has been stressed before, the concentration of NPK imported in food into cities presents the greatest challenge. The total net global flows of N, P and K estimated in the present study are 4.8 Tg in 1997 and 8.8 Tg in 2020. As Miwa (1992) points out, each country must consider the consequences of nutrient flows in food trade to its own ecosystem. For example, since livestock industries based on imported feeds create such massive nutrient disposal problems, the possibility of importing livestock products directly presents a solution. Government policies will determine such outcomes; the next section of this paper considers policy questions in detail. Further trends in international nutrient trade result from livestock production. Demand for livestock products is growing fast, especially in many developing countries. In Europe, about 60% of the total cereals available are used as animal feed, while worldwide this is 30%. Massive trade inFig. 3. Net flows of N, P, K in traded agricultural commodities in 1997 and 2020 (IMPACT model).444U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451feedstuffs involves transport from other continents to Europe, then conversion to meat and animal wastes in highly concentrated areas, with high emission rates to air and groundwater, where there is easy access by ship, train or roads for export of meat and milk to other countries (van Egmond et al., 2002). The return of nutrients to land-based systems via manure frequently causes problems due to high water content and high transport cost. While it is difficult to generalize, transport beyond 15 km is often uneconomical. In addition, mineral fertilizers, frequently a cheaper and more readily available source of nutrients, reduce demand for nutrients from manure even further, turning the latter into ‘‘waste’’. Surveys in Brittany have shown that, while the manure nitrogen would suffice, farmers bought an additional 80– 100 kg of nitrogen/ha per year in inorganic fertilizer. At the farm level, the type of management defines the environmental burden of this waste. At the regional level, the nutrient surpluses result from feed imports. With low levels of feed imports, such as prevailing in Denmark, almost all manure can be used on the farm. With large feed imports, such as in the Netherlands, regional imbalances emerge and transport costs become a critical issue.3. Policy recommendations 3.1. Agricultural trade liberalization and nutrient allocation Nutrient movements between nutrient deficit and surplus countries have been caused in part by agricultural policy distortions influencing agricultural trade patterns. In many developed countries, which count mostly as nutrient surplus countries, agricultural subsidies have boosted agricultural production to a large extent, while taxation has imposed constraints on agricultural production in many nutrient deficit developing countries. Overproduction of food and other agricultural products has led to environmental degradation from nutrient surpluses and artificially high exports in most developed countries. The United States, Europe and Japan spend a total of US$ 350 billion each year in agricultural subsidies. It is estimated that these farm subsidies cost poor countries about US$ 50 billion a year in lost agricultural exports. This is equal to the total aid provided by developed countries to developing countries (Kristof, July 6, 2002). As a result, developing countries have been unable to increase their investments in agriculture, including nutrient inputs. Due to their limited access to developed country markets, their returns have been decreased and based on cheap imports from developed countries their internal markets have also been distorted. Members of the World Trade Organization (WTO) acknowledged the need to further correct the prevailing restrictions and distortions in agricultural world markets byliberalizing agricultural trade. This is expected to have a major impact on production patterns and thus nutrient allocation world-wide. 3.1.1. Cutting domestic support in developed countries In Western Europe, a decrease and decoupling of agricultural subsidies is expected to avoid further massive surplus production and financial burdens in the context of the Common Agricultural Policy (CAP) in the future. Consequently, the intensity of production will decrease, and the growth in fertilizer use is expected to lag behind other regions of the world with a positive effect on the nutrient balance; this trend will be augmented by the increasing emphasis on organic agriculture (FAO, 2000). In the United States, however, subsidies will rise further under the newly launched US$ 180 billion farm bill. In contrast, in Australia and New Zealand, the agricultural sector was liberalized and all forms of subsidies were cut already in the late 1980s. Thus, the market encouraged the farmers to diversify according to their comparative advantage, not to produce according to the receipt of financial support by the government. The effects of subsidy removal can be shown in the example of New Zealand. In 1984, nearly 40% of the average sheep and beef farmer’s gross income came from government subsidies. In 1985, almost all subsidies were removed. About 15 years later, the agricultural sector in New Zealand has grown and is more dynamic than ever. The removal of farm subsidies has proven to be a catalyst for productivity gains. The diversification of land use has been beneficial for the farmers, and the farming of marginal land has declined. Overall, it has been found that the subsidies restricted innovation, diversification and productivity by corrupting market signals and new ideas. Instead, they lead to the wasteful use of resources negatively impacting on the environment (Frontier Centre for Public Policy, 2002). Since many of these environmental problems are associated with nutrient surplus, a major improvement in the management of nutrients is expected to result from liberalizing agricultural trade by cutting subsidies and reducing other kinds of policy distortions. In addition, as pointed out by Wonder (1995), input subsidies often mostly benefit those least in need, including large-scale farms and those with higher incomes. They also tend to distort the input mix used for farming through their encouragement of decisions based on support rather than commercial or production criteria. Runge (1996) concludes in his paper on subsidies in the agricultural sector that the elimination of most forms of subsidies in agriculture would produce a double benefit. This double benefit arises from an increasing economic efficiency and also from the reduced indirect negative environmental impacts of artificially expanded production. 3.1.2. Domestic support in developing countries In a survey of 38 developing countries, FAO found that 68% of them used fertilizer subsidies (FAO and IFA, 1999). InU. Grote et al. / Environmental Science & Policy 8 (2005) 439–451India, for example, the Government introduced subsidies for inputs like fertilizer, power, irrigation and credit to farmers in the late 1960s to foster agricultural growth. While these subsidies have been critical in getting the ‘Green Revolution’ started, the subsidies are now imposing high costs not only on the environment, but also on the fiscal budget. It has been found that the fertilizer subsidy, which keeps the price of nitrogen low leads to: (i) nutrient imbalances lowering the yield; (ii) declining quality of ground water; (iii) the inefficient use and waste of fiscal resources (World Bank, 2001). In Bangladesh, fertilizer subsidies were phased out as part of the overall market liberalization. In China, subsidies were removed by simultaneously increasing producer prices in compensation (FAO and IFA, 1999). Many other developing countries, especially landlocked and food-deficit countries in Africa, are characterized by allpervasive poverty, inadequate infrastructure, low fertilizer use and high fertilizer prices. Improving their opportunities to export to developed countries may increase their returns from agriculture, thus allowing them to invest more into their land by increasing their fertilizer input. In these cases, introducing a subsidy may actually help creating positive environmental externalities by giving incentives to the farmers to increase their fertilizer use to avoid soil fertility mining. Institutional constraints that often prevent the adoption of fertilizers in developing countries are generally related to a lack of access to markets leading to high transaction costs, or often also the existence of black markets (Tiessen, 1995). Efficient and appropriate organizations should be created to ensure that fertilizer reaches the farm on time, in adequate amounts, and at minimal cost. An improvement in the marketing of fertilizer is expected to increase their use in developing countries, thus avoiding further soil mining. One strategy to promote fertilizer use is to apply the ‘‘minipack’’ method in which small packets of 100 and 200 g of fertilizers are sold outside shops, in market places or outside churches (FAO and IFA, 1999). In general, the private sector should have the primary responsibility for marketing and distribution of fertilizer, while the government should develop and implement appropriate regulatory and quality control measures for efficient functioning of the fertilizer markets. In those areas where markets are underdeveloped, the Government may take the lead in developing markets and supporting infrastructure. Furthermore, poor land tenure security, especially in the rainfed mixed farming systems of the developing world, as well as poor access to credit provide a disincentive for investment in long-term soil fertility improvements (Bumb and Baanante, 1996). 3.1.3. Integrating different production systems Past trade policies in developing countries have also often limited the synergistic effect of crops and livestock in nutrient deficient situations. Imposing high import duties to protect domestic cereal production have pushed cropping445into marginal areas and upset the equilibrium between crops and livestock. In the former centrally planned economies, industrial systems have also benefited greatly from policy distortions, which in many cases have given these systems a competitive edge over land-based systems. Beef feedlot enterprises were based on heavily subsidized feed grain and on subsidized fuel and transport. In many developing countries, however, there are often no direct subsidies on feed and on energy. Since energy is a major direct and indirect cost item in industrial production systems, economy-wide policies such as subsidies tend to favor them over their land-based counterparts. For agriculture, there are good possibilities to optimize nitrogen efficiency by integrating livestock and crop production. The integration still represents a major avenue for intensification of food production. To varying extents, mixed farming systems allow the use of waste products of one enterprise (crop by-products, manure) as inputs to the other enterprise (as feed or fertilizer). Mixed farming is, in principle, beneficial for land quality in terms of maintaining soil fertility. In addition, the use of rotations including various crops and forage legumes replenishes soil nutrients, and reduces soil erosion as well as the risk of pests and diseases common in cereal monoculture (Thomas and Barton, 1995). Adding manure to the soil increases the nutrient retention capacity, improves the physical condition by increasing the water-holding capacity and improves soil structure stability. This is a crucial contribution because, in many systems, it is the only avenue available to farmers for improving soil organic matter. It is also substantial in economic terms. Approximately, 20 million tonnes or 22% of the total nitrogen fertilization of 94 million tonnes (FAO, 1997) and 11 million tonnes or 38% of phosphate is of animal origin, representing about US$ 1.5 billion worth of commercial fertilizer. Not only does animal manure replenish soil fertility but it helps to maintain or create a better climate for soil micro-flora and fauna. It is also the best way of using crop residues. As population pressure changes the crop/grazing land ratio, and if other sources are not available, soil fertility gaps widen. In input-intensive urban farming in nutrient deficit countries, the high load of nutrients can be washed into rivers or ground water, thus contributing to water eutrophication (Kyei-Baffour and Mensah, 1993). Nevertheless, some of these nutrients might re-enter the system by contributing to the nutrient requirements of irrigated crops. This is consistent with interviews held with some farmers who believe that water provides a detectable fertilizer benefit to their crops (Cornish et al., 1999). Thus to some extent the off-site costs of water eutrophication might be balanced by the fertilizer value of the water. Reductions of fertilizer use may also be achieved by shifting to a human diet with less animal protein. However, human diets are generally not the subject of policy446U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451formulation but can be influenced through strategies such as marketing and raising public awareness (van Egmond et al., 2002). 3.2. Control and command measures In OECD countries, nutrient excess situations are increasingly regulated, alleviating some of the environmental hazard. There are a number of measures, which set certain regulations for the use of chemical fertilizers, such as: requirement for fertilizer nutrient management plans; maximum application amounts; regulation of times of application in order to reduce leaching and volatilisation; and severely limited use of fertilizers in e.g. water extraction areas and nature protection areas. With respect to organic fertilizers, additional measures include: maximum numbers of animals/ha based on the amount of manure that can be safely applied per ha of land; holdings wishing to keep more than a given number of animals must obtain a license; and minimum capacity for manure storage facilities. In cases of non-compliance with these regulations, fines and other legal enforcement measures are applied to combat environmental degradation. However, it must be mentioned that there is ample evidence of lack of enforcement of environmental regulations and laws, especially in developing countries. As an example of a control and command measure, the European Union (EU) has introduced in 1991 the nitrates directive to combat water pollution from agriculture. The directive includes the obligation of member states to designate so-called nitrate vulnerable zones (NVZs). Nitrate concentrations in water in these zones are to be reduced to values below 50 mg/l. In addition to the codes of good agricultural practice, valid on a country-wide basis and often consisting of voluntary-based measures, specific action programs with mandatory measures have to be developed for the NVZs. These action programs include measures like: a proscribed period for fertilizer application; restrictions to applications on sloped soils and on soaked, frozen or snowcovered soils; limitations to applications near watercourses; and mandatory minimum capacity limits for manure storage and fertilization plans. Besides compulsory measures, also voluntary measures like frequent sampling and analysis of manure are promoted. An assessment of the directive has shown that farmers’ awareness about water pollution and the need to protect water has increased. Action programs are valuable tools to enforce measures that lead to a reduction of water pollution by agricultural activities. Regional projects show that significant improvements can be achieved e.g. in terms ofreduced fertilizer inputs while maintaining the economic potential of agriculture (Monteny, 2002). Another example for command and control measures can be found in Flanders, Belgium. There, the agricultural sector accounts for two-thirds of nitrogen losses to the environment. The nitrogen surplus amounted to 187 million kg N or 294 kg/ha, which equalled almost half of the inputs. Comparing OECD statistics, it can be seen that Flanders nitrogen balance is even higher than that of the Netherlands. To reduce the nitrogen surplus, a number of different measures have been applied: Initially, the manure policy was aimed at distributing the manure surplus equally across Flanders and at stopping the growth of livestock by a strict licensing policy. Soil-less livestock farms usually need to have contracts with feed producers. Later on, the policy switched to the use of individual target commitments by farmers. Command and control policies alone are often inefficient, and require supplementary market-oriented policies to enhance the effectiveness of environmental protection. Implementation of control measures at the farm level will only be successful and sustainable if the farmer can determine his or her economic interest to undertake such measures. Therefore, the economic benefits from such factors as implementation of erosion control measures to maintain soil fertility, capital costs associated with improved manure handling and distribution, etc. must be clearly seen to be offset by reduced energy consumption in minimum till situations, improvement in soil fertility by improved manure handling and erosion control, reduced fertilizer costs etc. In addition, it should be mentioned that the establishment of nutrient accounting systems combined with financial accounting systems has been suggested as an important audit system and as a policy instrument. Bookkeeping of inputs and outputs at the level of individual farms has been selected as a new solution to control nutrient use and to tax nutrient surpluses in agriculture. At the same time, nutrient accounting presents important management information (Breembroek et al., 1996). 3.3. Voluntary measures The adoption of diverse voluntary measures, practices and technologies has the ability of minimizing adverse environmental effects. In order to improve nitrogen efficiency, ‘Best Agricultural Practice’ has been promoted. Decreasing or optimizing the production and use of chemical fertilizer is an effective means of changing the amount of nitrogen in the system. However, a reduction of chemical fertilizer is only possible in an agricultural operation where organic manure can serve as an alternative. Next to codes of best practice, the promotion of the ‘‘polluter pays principle’’ (PPP) aims at internalizing environmental costs resulting from nutrient overflow at the farm level. A case study in Pennsylvania has, for example, shown that the net farm income without natural resource accounting amounted to US$ 80 compared to US$ 27 when theU. Grote et al. / Environmental Science & Policy 8 (2005) 439–451environmental costs had been factored in; so, there is a big gap between private and social cost accounting in the presence of environmental externalities (Runge, 1996; Faeth et al., 1991). Also eco-labeling might be a useful measure to show that no or less fertilizer and pesticides have been used, thus benefiting the environment. Eco-labeling is defined as a practice of providing information to consumers about a product, which is characterized by improved environmental performance and efficiency compared with similar products, and it has gained increasing popularity in recent years. It is considered as an attractive policy measure because of its voluntary nature and market-driven approach to achieve environmental goals. The idea is that growing concern of consumers for the environment encourages them to pay relatively higher prices for agricultural products, which have been produced in an environmentally friendly way. Producers have the incentive to pay more attention to the environmental effects of their production processes and to the quality of their final products. As an outcome, they receive higher prices, so-called price premiums, for their products. Most of the agricultural products, which are certified, are produced in systems based on organic farming or integrated pest management. However, eco-labeling also presents challenges and has raised concerns, especially in developing countries but also among many consumers in developed countries.3 3.4. New economic approaches New economic approaches involve full resource valuation and full cost pricing of resources. Often, a judicious mix of market-based instruments and standard setting is the most appropriate approach. It must be also considered that each country situation is different, and while the choice of instruments may be similar, their designs are very different (UNEP, 1999). In the following, economic analysis and nutrient trading permits are presented as new economic approaches towards a more efficient nutrient management. 3.4.1. Economic analysis An important issue in the preparation and choice of environmental policies is the evaluation of their costs imposed on all farm sizes. Some policy options are more beneficial to certain size operations than others. A comparison between the environmental or social benefits with the economic costs for different policy measures provides a basis for selecting the most appropriate and lowest cost policy options at the national level (Kjaer and Narrod, 2000). Economic analysis can provide a guide to the level of actions required to reduce nitrogen losses and environmental3 For a literature review on the role of eco-labeling in agriculture, see Grote (2002).447risks in a cost-effective manner, while also allowing consideration of relative costs of controls to various groups. Research on alternative policies for reducing nutrient loads to the Gulf of Mexico has been conducted (Doering et al., 2002). Comparisons were based on the evaluation of the social and economic costs and benefits of methods for reducing nutrient loads. Two basic approaches were taken: first, the amount of N reaching the surface waters in the Mississippi Basin was to be reduced; second, the N concentration already in the waters within the basin flowing to the Gulf was to be reduced. The analysis indicates that N losses from agriculture can be reduced in the 20% range through either nutrient restrictions or programs aimed at reducing N losses. A modest area of wetlands (1–2 million acres) can be restored in a cost-effective manner. The strategies combined would not greatly affect farm prices or consumer food costs. However, some farmers would have higher costs of following a program than others. For example, farmers on marginal soils or in drier areas may have limited flexibility in trying to meet N-reduction goals (Doering et al., 2002). It is not possible to know the full costs of the specific program be they wetlands restorations, N restrictions, or N loss reductions requiring incentives. Further it has been calculated based on a model4 that as N was restricted or N losses were controlled, production declined and agricultural prices increased. For example, a 20% fertilizer restriction resulted in a 6% increase in corn prices and a 2% increase in wheat prices. A 40% restriction resulted in a 28% increase in corn prices and a 13% increase in wheat prices. Management of agricultural N requires estimates of integrated budgets, which may be considered in relation to national agricultural soil surface areas. For effective management of N, reliable data and budgets are required for identifying relevant emission sources, and for helping policy makers to select possible options for control. Ideally agricultural budgets should be considered on a farm-by-farm basis, which provides detailed datasets to help increase the awareness of the farming community and identify inefficiencies. For international agreements, there is a strong need for comparable, reliable, up-to-date data provided on a continuous basis. Balance sheets are an important tool. When looking at regional or national solutions special relocation of functions (nature, agriculture) might provide the means to solve some local problems. 3.4.2. Nutrient trading permits Low-cost, innovative approaches are needed to effectively reduce pollution from non-point sources like agriculture and urban runoff. Emission trading is being proposed as a new instrument in environmental policy to 4 The US Mathematical Programming (USMP) model was developed by USDA’s Economic Research Service to analyze the effects of government commodity programs and environmental policies on the US agricultural sector and the environment.448U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451potentially solve nutrient discharge problems. Emission trading has been used to create markets in air or water pollution. In addition, trading is the leading option proposed to address the build-up of greenhouse gas emissions that could cause climate change. For trading, an overall level of permissible pollution is set. The permissible aggregate level of pollution is lower than the current level, so that an artificial scarcity is created and the permits acquire market value. The permits divide this level between producers based on norms agreed by policymakers. Producers who wish to expand their production, for example, need to reduce the pollution from their own production sites or buy permits from others. Thus, trading increases flexibility and reduces costs by allowing producers with new obligations the option of adapting their own facilities or financing comparable reductions by others. Sources with low treatment costs on the other hand may reduce their own effluents beyond legal requirements, generate a credit, and sell these credits to dischargers with higher treatment costs. This flexibility produces a less expensive outcome overall while achieving – and even going beyond – the mandated environmental target. The desired reduction in pollution occurs at least cost. However, there have been also cases where administrative and transaction costs increased, making trading difficult. Faeth (2000) compared different policy approaches to reduce phosphorus loads in specific watersheds in the US. He estimated that one variation utilizing trading, costs about US$ 2.90 per pound of phosphorus removed, compared to almost US$ 24 per pound for conventional point-source requirements. He therefore recommends trading among industrial and municipal point sources whenever new nutrient reduction requirements are put in place. EPA estimates that if background pollution from agriculture were reduced, the need for tertiary water treatment could be avoided—providing a net saving of US$ 15 billion in capital costs for tertiary treatment (cited by Faeth, 2000). Dekkers (2002) notes that the implementation of an emissions or pollutant trading scheme requires a number of difficult changes in people’s perceptions and attitudes. King and Kuch (2003) note that there are about 37 trading programs in the US but only a few actually traded nutrient credits. They find that institutional obstacles are significant but can be overcome. Instead, problems related to inadequate supply and demand are the primary obstacles, which are difficult to overcome. These include, for example, state and federal water and agricultural policies in terms of regulatory and/or subsidy programs which require and/or pay farmers to implement nutrient management practices. They further conclude that nutrient trading should only be promoted in areas with favorable supply and demand conditions. To make a tradable permit system feasible, it is necessary to base it on indicators easy to obtain. Perez and Britz (2003) suggest to calculate harmonized European emission coefficients. These would be based on the size of the animal herd and the fertilizer use at the farm level, multiplied by fixed factors and finally added up to totalemissions which would then need to be declared. The administrative burden accruing to farmers would be rather low since this information is also needed to calculate nutrient balances or when asking for direct income support. A new scientific approach – a concept of optimum nitrogen management for society – has been suggested as an alternative or complement to the critical load/critical level approach now widely used in Europe. This concept is based on the idea of an optimum but extends this concept to include all types of land use within society. With an optimum curve in place for each type of land use and each curve translated into emission ceilings, which do not exceed critical limits, various economic and regional sectors of society could negotiate and then adjust emissions accordingly in a cost-effective way for a more sustainable and equitable society. Finally, it should be mentioned in this context, that policies aimed at solving environmental problems associated with nutrient surplus (mostly nitrogen and phosphorus) must often be multinational in scale. To foster coordination at a higher level, very often information exchange needs to be increased. For example, the N input to the North Sea is subject to the North Sea action plan and the OSPAR convention. Reductions of up to 50% have been agreed on by Rhine and North Sea countries.4. Summary and conclusions The expansion and intensification of agricultural production to meet the needs of a burgeoning population has transformed vast areas of the land surface. These changes have perturbed nutrient cycles in the soil–water–plant– atmosphere continuum at a range of scales, from farm to global levels. The contrasts between the nutrient balance of agricultural soils in nutrient deficit and in nutrient surplus countries reflect the large disparities in wealth, farmer use of purchased nutrient inputs, and agricultural policies between less developed and industrialized countries, respectively. The consequential environmental and ecological impacts of nutrient flows within and between countries require more study. One particularly neglected area is the impact of the international movement of nutrients in traded agricultural commodities. This paper addresses some of these knowledge gaps by reviewing and presenting data on global nutrient movements, and by considering a wide range of government policies that impinge on nutrient availability and flows. Nutrient movements in traded agricultural commodities provide a unique international dimension to nutrient flows. We obtained net trade data for major food commodities for 1997 from FAO and for 2020 used projections from the International Food Policy Research Institute IMPACT model. Commodity trade data for different regions and countries were converted to weights of N, P, and K using average nutrient contents from the literature. The results show that international net flows of NPK vary widely acrossU. Grote et al. / Environmental Science & Policy 8 (2005) 439–451regions, but amount to 4.8 Tg in 1997 and are projected to increase to 8.8 Tg in 2020, representing a major humaninduced perturbation of global nutrient cycles. Major net importers of NPK in traded agricultural commodities are West Asia/North Africa and China. Despite a widely recognized problem of soil nutrient depletion, sub-Saharan Africa is a net importer of NPK in agricultural commodities (0.3 Tg in 1997 and 0.6 Tg in 2020). However, nutrients imported in food and feed commodities to sub-Saharan countries are commonly concentrated in the cities creating waste disposal problems rather than alleviating deficiencies in rural soils. Countries with a net loss of NPK in agricultural commodities are the major food exporting countries—the United States, Australia, and some countries of Latin America. In the case of the United States, exports of NPK will increase from 3.1 Tg in 1997 to 4.8 Tg in 2020. When these data were expressed as a percentage of fertilizer consumption in the United States, net exports in 1997 were the equivalent of only 18% of its fertilizer consumption. Equivalent data for China, the largest importer, show only 2% in 1997. On the other hand, because of its small land area, Japan will import in commodities the equivalent of 90– 100% of its fertilizer consumption, and because of the low current rates of fertilizer use, sub-Saharan Africa will import as much as 26% in 1997. A wide range of policy measures influence agricultural trade, nutrient flows and balances. Agricultural trade liberalization and the reduction of production subsidies were expected to reduce excessive nutrient use in nutrient surplus countries and make inputs more affordable to farmers in nutrient deficient countries. In an ideal world, this should result in a more efficient global allocation of natural resources and nutrients and reduced environmental costs, although some level of subsidy to developing country farmers may be justified to introduce them to fertilizer technologies. Policies that encourage diversified production systems should have similar effects by ensuring that animal wastes are not concentrated in areas with no opportunities to recycle nutrients on arable crops. Other measures include more direct environmental policies to regulate nutrient disposal, as exemplified by the recent nutrient accounting scheme in the Netherlands. Alternative voluntary approaches include the promotion of best agricultural practice or eco-labeling. For nutrient surplus countries, innovative policy options such as nutrient trading are being examined. For nutrient deficient countries, institutional strengthening and infrastructure development are valid approaches that entail credit schemes, extension, training, etc. Our study highlights the need for environmental costs to be factored into the debate on nutrient management. Such costs include moving and disposing of waste from millions of tonnes of nutrients in feed grains used for intensive livestock production. It costs governments billions of dollars to establish and control elaborate environmental regulations to avert water and atmospheric pollution, and it costs society449even more when these regulations fail. Because of the increased demand for meat as incomes rise in developing countries, meat-exporting industrialized countries will increase production to meet the demand, increasing the hot spots of nutrient pollution in those countries, and the costs will be passed on to their tax-payers. Knowledge of the scope and the long-term costs of these problems should prompt societies and politicians in these countries to support reductions in agricultural subsidies and opening up their markets. On the other hand, given a level playing field and a helping hand, developing countries could expand their livestock production in environmentally benign and profitable ways. The resulting economic development would reduce the need for handouts and probably help stem the out migration from developing countries. We advocate more inter-disciplinary research on these important problems, and solutions such as that proposed above. While hydrologists, soil scientists or engineers determine, what is technologically feasible and set maximum allowances, economists identify the relatively cost-effective options and their distributive effects. The results of the research should better inform the public whose perceptions and values play a major role in the final choice of the policy measures. Appendix A. IFPRI IMPACT commodities and nitrogen, phosphorus and potassium contents ProductsUnitsNutrient content NBeef Pork (pig meat) Sheep/goat Poultry Eggs (whole egg) (USA) Milk (whole milk) (cow) Wheat Maize Rice (grain and hulls) Other coarse grains Barley Millet/canary grains Oats Rye (cereal rye) Sorghum Potatoes (tubers) Sweet potatoes Cassava and other roots and tuberscassava Soybeans Meals Oilskg/tonnes kg/tonnes kg/tonnes kg/tonnes kg/tonnes kg/kL kg/tonnes kg/tonnes kg/tonneskg/tonnes kg/tonnes kg/tonnes25 24 23 24 16.8 5.3 21 11.7 9.2 15.6 18 17.8 14.2 12.5 15.3 3 2.4 2.6kg/tonnes kg/tonnes kg/tonnes17 32.1 0P 2.1 5.6 1.6 1.5 2.6 0.93 2.3 2.1 2.1 2.6 2.4 2.9 2.4 3.0 2.1 0.4 0.5 0.4 20 0.8 0K 3.5 2.2 2.4 2.7 1.2 1.6 3.2 2.4 2.6 3.6 3.8 3.5 3.6 4.1 3.0 4.4 3.7 2.9 16.4 6.8 0Sources of nutrient concentration data: Beef (N, P, K): Asian Livestock (2000); Sheep/goats, chicken: Souci et al. (1969); Pork (pig meat), Eggs, Milk, Wheat, Maize, Rice. Other course grains: Potatoes (tubers), Sweet potatoes, Cassava (N, P, K): NLWRWP (2001); Soybeans (For N and P): FAO (2002) Animal Feed Resources Information System, (For K): Stanton (1999); Meals (For N and P): FAO (2002) Animal Feed Resources Information System, (For K): Stanton (1999); Oils (N, P, K): USDA (2002).450U. Grote et al. / Environmental Science & Policy 8 (2005) 439–451Appendix B. NPK flows in net trade in 1997, also expressed as a percentage of NPK fertilizer consumption in 1997, and net trade flows of NPK in 2020 (Tg) Countries/regionsTotal NPK consumption (1997) (Tg)USA EC15 Japan Australia Other developed countries Eastern Europe Former USSR Latin America Sub-Saharan Africa West Asia/North Africa South Asia South East Asia China Rest of the world17.003 13.570 1.105 1.530 3.687 3.239 3.949 8.950 1.012 4.899 17.412 6.463 29.870 0.029Total NPK in net trade (1997) (Tg) 3.066 0.760 0.974 0.611 0.527 0.148 0.148 0.646 0.266 1.260 0.044 0.331 0.600 0.017References Asian Livestock, 2000. Buffalo meat: the most economical source of protein. Asian Livestock, FAO Regional Office, Bangkok Thailand, 24 (2), pp. 11–13. Breembroek, J.A., Koole, B., Poppe, K.J., Wossink, G.A.A., 1996. Environmental Farm Accounting: The Case of the Dutch Nutrients Accounting System, 51. Elsevier Science Ltd, Agricultural Systems, pp. 29–40. Bumb, B.L., Baanante, C.A., 1996.In: Policies to Promote Environmentally Sustainable Fertilizer Use and Supply to 2020, IFPRI, Washington, DC, 2020 Vision Brief 40, October 1996. Cornish, G.A., Mensah, E., Ghesquire, P., 1999. An Assessment of Surface Water Quality for Irrigation and its Implications for Human Health in the Peri-Urban Zone of Kumasi, Ghana. Report OD/TN 95 September 1999. HR Wallingford, UK. Dekkers, Chris, P.A., 2002. NOx Emission Trading in a European Context: Discussion of the Economic, Legal and Cultural Aspects. In: Optimizing Nitrogen Management in Food and Energy Production and Environmental Protection, Proceedings of the Second International Nitrogen Conference on Science and Policy. The Scientific World (2001), pp. 958–967. Doering, O.C., Ribaudo, M., Diaz-Hermelo, F., Heimlich, R., Hitzhusen, F., Howard, C., Kazmiericzak, R., Lee, J., Libby, L., Milon, W., Peters, M., Prato, A., 2002. Economic Analysis as a Basis for Large-Scale Nitrogen Control Decisions: Reducing Nitrogen Loads to the Gulf of Mexico. In: Optimizing Nitrogen Management in Food and Energy Production and Environmental Protection, Proceedings of the Second International Nitrogen Conference on Science and Policy. The Scientific World (2001), pp. 968–975. Drechsel, P., Gyiele, L.A., 1999. The Economic Assessment of Soil Nutrient Depletion. Analytical Issues for Framework Development. International Board for Soil Research and Management. Issues in Sustainable Land Management No.7. Bangkok. Faerge, J., Magid, J., Penning de Vries, F.W.T., 2001. Urban nutrient balance for Bangkok. Ecol. Model. 139, 63–74. Faeth, P., 2000. Fertile Ground—Nutrient Trading’s Potential to CostEffectively Improve Water Quality. World Resources Institute, Washington, DC. Faeth, P., Repetto, R., Kroll, K., Dai, Q., Helmers, G., 1991. Paying the Farm Bill: US Agricultural Policy and the Transition to Sustainable Agriculture. World Resources Institute, Washington, DC. FAO, 1997. Current World Fertilizer Situation and Outlook 1994/1995– 2000/2001. FAO/UNIDO/World Bank Working Group on Fertilizers, Rome.NPK in net trade as a % of 1997 NPK consumption (1997) (%) 18 6 88 40 14 2 4 7 26 26 0 5 2 58Total NPK in net trade (2020) (Tg) 4.757 0.662 1.116 0.859 0.856 0.244 0.116 1.951 0.628 2.086 0.607 0.771 2.152 0.032FAO and IFA, 1999. Fertilizer Strategies. Food and Agriculture Organization of the United Nations and International Fertilizer Industry Organization, revised version, Rome. FAO, 2000. Fertilizer Requirements in 2015 and 2030 (ftp://ftp.fao.org/agl/ agll/docs/barfinal.pdf; accessed on 08 January 2004). FAO, 2002. Animal Feed Resources Information System (http:// www.fao.org/DOCREP/003/W6928E/w6928e1k.htm; accessed 8 March 2000). Frontier Centre for Public Policy, 2002. Life after Subsidies. The New Zealand Farming Experience—16 Years Later. In: Frontier Backgrounder, Frontier Centre for Public Policy, February 2002. Galloway, James N., Cowling, Ellis B., 2002. Reactive nitrogen and the world: 200 years of change. Ambio 31, 64–72. Grote, U., 2002. Eco-labeling in the agricultural sector: an international perspective. In: European Council, Proceedings of the High-Level Pan European Conference on Agriculture and Biodiversity: Towards Sustainable Agriculture in Europe Integrating. King, D.M., Kuch, P.J., 2003. Will Nutrient Credit Trading Ever Work? An Assessment of Supply and Demand Problems and Institutional Obstacles. Environmental Law Institute, Washington, DC, 33 ELR, pp. 10352–10368. Kjaer, S., Narrod C., 2000. Economics and Policy Options (http://lead.virtualcentre.org/en/ele/awi_2000/6session/6paper.htm; accessed 12 August 2002). Kristof, N.D., Agricultural absurdity. International Herald Tribune (IHT), 6 July 2002. Kyei-Baffour, N., Mensah, E., 1993. Water Pollution potential by agrochemicals. A case study at Akumadan. In: Proceedings of the 19th WEDC Conference, September ’93, Accra, Ghana, pp. 301–302. Milliman, J.D., Meade, R.H., 1983. Worldwide delivery of river sediment to the oceans. J. Geol. 91, 751–762. Miwa, 1992.In: Global nutrient flow and degradation of soils and environment: Transactions 14th International Congress of Soil Science, vol. V, Kyoto, Japan, August 1990, pp. 271–276. Monteny, G.J., 2002. The EU Nitrates Directive: A European Approach to Combat Water pollution from Agriculture. In: Optimizing Nitrogen Management in Food and Energy Production and Environmental Protection, Proceedings of the Second International Nitrogen Conference on Science and Policy. The Scientific World (2001), pp. 927–935. National Land and Water Resources Audit Project, 2001. Nutrient Balance in Regional Farming Systems and Soil Nutrients Status. Australian National Heritage Trust (CD-ROM). Perez, I., Britz, W., 2003. Europaweite Reduktion des Ausstoßes klimarelevanter Emissionen durch handelsbare Emissionsrechte. Eine AnalyseU. Grote et al. / Environmental Science & Policy 8 (2005) 439–451 mit dem regionalisierten Agrarsektormodell CAPRI. Beitrag zur Gewisola-Tagung, Hohenheim, 29.09.-01.10.2003. Rosegrant, M.W., Paisner, M.S., Meijer, S., Witcover, J., 2001. 2020 Global Food Outlook: Trends, Alternatives and Choices. International Food Policy Research Institute, Washington, DC. Runge, F., 1996. Subsidies and Environment. Exploring the Linkages. OECD, Paris, pp. 139–162. Seitzinger, S.P., Kroeze, C., 1998. Global distribution of nitrous oxide productions and N inputs in freshwater and coastal marine ecosystems. Global Biogeochem.. Smil, V., 2001. Enriching the Earth: Fritz Haber. In: Carl Bosch and The Transformation of World Agriculture, The MIT Press, Cambridge, MA. Souci, S.W., Fachman, W., Kraut, H., 1969. Die Zusammensetzung der Lebensmittel: Naehrwert-Tabellen. Wissenschaftliche Verlagsgesellschaft, Stuttgart. Stanton, T.L., 1999. Feed composition for cattle and sheep. Colorado State University Cooperative Extension Livestock Series No.1.615. Stoorvogel, J.J., Smaling, E.M.A., 1990. Assessment of soil nutrient depletion in sub-Saharan Africa: 1983–2000. Report 28, The Winand Staring Center, Wageningen, The Netherlands. Thomas, D., Barton, D., 1995. Interactions between Livestock Production Systems and the Environment Impact Domain: Crop-Livestock Interactions. Working Document Livestock and the Environment: Finding a Balance, FAO/World Bank/USAID, Rome. Tiessen, H., 1995. Scope 54 – Phosphorus in the Global Environment – Transfers, Cycles and Management (http://www.icsu-scope.org/execsum/ scope54.htm; accessed 30 July 2002). UNEP, 1999. Global Environment Outlook GEO-2000. UNEP, Nairobi. USDA, 2002. National Agricultural Laboratory (http://www.nal.usda.gov/ fnic/cgi-bin/list_nut.pl; accessed 2 April 2002). van der Hoek, K.W., 1998. Nitrogen efficiency in global animal production. Environ. Pollut. 102, 127–132. van Egmond, K., Bresser, T., Bouwman, L., 2002. The European Nitrogen Case. Ambio vol. 31, No. 2, March, Royal Swedish Academy of Sciences, pp.72–78. Vitousek, P.M., Mooney, H.A., Lubehenco, J., Melillo, J.M., 1997. Human domination of earth’s ecosystems. Science 277, 494–499.451Vlek, P.L.G., 1993. Technologies for agriculture in the tropics. Strategies for sustaining agriculture in sub-Saharan Africa: The Fertilizer Technology Issue, 56. ASA Special Publication, Madison, WI, USA, pp. 265–278. Vlek, Paul, L.G., Ku¨hne, R.F., Denich, M., 1997. Nutrient resources for crop production in the tropics. Phil. Trans. R. Soc. Lond. B 352, 975–985. Wonder, B., 1995. Department of Primary Industries and Energy, Australia, Australia’s Approach to Agricultural Reform. Washington, DC, March 13. World Bank, Energy Sector Unit, 2001. India: power supply to agriculture. vol. 1, Summary Report No.22171-IN. Ulrike Grote studied agricultural economics at the University of Kiel. After receiving her Ph.D. from Kiel in 1994, she worked at the OECD in Paris and the Asian Development Bank in Manila. Since 1998, Ulrike Grote has worked at the Center for Development Research (ZEF) in Bonn. In December 2003, she finished her habilitation. Her research focuses on international agricultural trade, environmental and development economics. Eric Craswell specialized in soil microbiology and soil fertility at the University of Queensland and was awarded his Ph.D. in 1973. He worked on nitrogen cycling and the efficiency of fertilizers for cereal crops at centers in Queensland, Alabama, and the Philippines. After an extended period in research management in the field of land and water resources, he developed an interest in nutrient and water cycling at the global scale and serves as Executive Officer of the Global Water System project based at ZEF in Bonn. Paul Vlek is Professor at the University of Bonn and Executive Director of its Center for Development Research. He holds a Ph.D. in Soils and Agronomy. His research interests are sustainable development in the developing world, management of natural resources and ecosystems in a world subjected to global change. Specifically, he is concerned with water, soil degradation and nutrient cycles and means to optimize the allocation of these scarce resources to the benefit of communities and society as a whole.