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Presented at the 2000 IFA Regional Conference for Asia and the Pacific
4-7 December 2000, Yokohama, Japan
Impact of urbanization upon fertilizer usage
Revised version
Dr. A. Krauss - Director, International Potash Institute, IPI, POB 1609, CH-4001 Basel, Switzerland. Tel. +41 61 261 29 22; Fax +41 61 261 29 25; e-mail: ipi@ipipotash.org website: http://www.ipipotash.org
Contents
Summary
Urbanization can pose a major problem in developing countries. Not only does it force the planners to provide more, and more adequate, dwellings, water and power supply, traffic and transport opportunities, but also more food, at prices affordable for the low income class, and at the same time diverse and of high quality for the emerging middle/upper class. On the other hand, the remaining rural society, being confronted with the migration of the younger generation into towns, not only needs the means to maintain land productivity with a reduced labour force, but also has to feed more people not involved in agriculture. Some of these aspects are discussed in the following chapters:
- Urbanization challenges food production
- Urban centers accumulate nutrients
- Increasing demand for meat - implications for fertilizer use
- Change in crop spectrum towards vegetables and oilseed and its impact on nutrient management
- Focus on quality necessitates balanced fertilization
Urbanization challenges food production
Global population increases annually by almost 80 million people. Although the growth rate will decline, it is expected that the global population will hit the 8 billion mark within the next 20 years.
Half of the additional 2 billion people will grow up in Asia. FAO (1998) estimates that the current population of about 3.7 billion will increase to 4.6 billion in the next 2 decades and to almost 5.5 billion by the middle of this century.
At the same time, progressively more people leave the rural area searching for jobs and food. Urbanization in Asia, which is already as high as 80% in the developed countries, will further increase in developing countries like China from currently 36% to more than 50% by the year 2020 (figure 1).
| Figure 1: Demographic evolution of Asian Regions | |
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| FAOSTAT 1998 |
More people need more food. As an example, Argenti (2000) estimates that food requirement of urban centers like Isfahan, Iran will increase in the next 10 years by 7 million t to more than 20 million t, and Karachi, Pakistan by more than 20 million t to almost 64 million t of food. Assuming that 80% of the diet is based on cereals, the future food demand for Karachi would call for almost 1 million t N, 0.4 million t P2O5 and 0.25 million t K2O.
Low value subsistence crops like cereals and root crops make the major contribution to the total food requirement of low-income inhabitants of urban centers in developing countries (figure 2). But, with increasing income, the diet changes to include more animal protein, high quality vegetables and fruits. Urbanites in China for instance eat more meat (27 kg per capita) and less rice (68 kg) than their rural counterparts (17 kg meat and 103 kg cereals (Rozelle & Jikun Huang, 1999). The per capita supply with vegetables in the wealthy Asian countries like Japan at 94 kg is more than twice that in developing countries like Vietnam (45 kg) (FAO, 1998). Bangladesh intends to reduce the contribution of cereals to total calorie intake from currently 83% to 55% by 2020, and correspondingly to increase the share of meat, vegetables and fruits from currently 8% to 15% (Bhuiyan, 1998).
In due course the wealthy 'high-tech' society spends less time on food preparation and looks for packed and processed food. Furthermore, there is considerable public concern about nitrate in vegetables, growth hormones and antibiotics in meat products or the cases of BSE in Europe which increases the desire for safe food of 'bio' origin. The market share of bio-food although still rather small will grow. In 1997, the US market for organic products was $4 billion, up from $78 million in 1980; European consumers spend about $4.5 billion on organic products and Japan around $2 billion per year (Swezey & Broome, 2000). Sweden has set a goal of converting 20 percent of its farm acreage to organic farming by 2005 (IFA, 2000).
| Figure 2: Income and food type | |
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| after Kern, 2000 |
There is increased interest in functional food which may have a potential to lower body fat, cure gut maladies, provide gender- and age-related medical needs, improve skeletal strength, lower cholesterol or improve eyesight etc. (Kern, 2000). Ingredients such as lycopene in tomato, allicin in garlic or isoflavones in soybean are associated with prevention or treatment of cancer, diabetes, hypertension, and heart disease (Bruulsema, 2000). Rice has been genetically modified to synthesise and accumulate beta-carotene (provitamin A) or to contain 3 times as much iron as conventional rice, i.e. factors involved in controlling eyesight and anemia, respectively (Goto et al., 1999; Gura, 1999; Ye et al., 2000).
What are the consequences of the dynamic changes in food habit as affected by urbanization for fertilizer use and nutrient management?
1. Urban centers accumulate nutrients
Carrying food into towns transfers nutrients from the agricultural area into the urban centers (figure 3). The nutrient transfer increases with urbanization. On a world scale about 175 million t N + P2O5 + K2O are removed annually with harvested crops. Assuming a global rate of urbanization of 47.5%, this means that at least 83 million t NPK are transferred into towns. Another example: assuming that at least half of the total vegetable production of 402 million t in Asia is consumed in towns, this represents the transfer of about 1.8 million t N, 0.4 million t P2O5 and 0.6 million t K2O.
| Figure 3: Schematic view of nutrient cycles | |
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Usually, the nutrients excreted after digesting the food in towns are deposited in urban dumping sites. Health concerns, mixing with toxic and/or heavy metals are some of the reasons for farmers to hesitate to use sludge from urban sewage plants. However, agriculture in West Europe for instance is put under increasing pressure to accept and recycle urban sewage sludge because alternative disposals on dumping sites or in waste incineration plants have become quite expensive. Still, the administrative procedure is quite high because the mud and the soil after application have to be analyzed to control transfer of unwanted organic/inorganic substances to the arable land and into the food chain. As an incentive, the farmers in EU, who recycle urban sewage sludge, get subsidies to use the waste material, their soils are analyzed by the supplier and they get advice free of charge. Nutrient-wise sewage sludge is mostly a source of phosphorus and nitrogen and less of potassium. Estimates from EFMA (2000) show that about 2.6% of nitrogen, 3.5% of P2O5 and 1.1% of K2O used in EU agriculture derive from non-livestock urban waste.
Another source of nutrients from urban centers is organic waste from households, plant residues from home gardens, lawn cuttings, etc. In the form of compost, it is a good source of potassium in particular and of humus. However, the bulkiness, low nutrient content, possible contamination with heavy metals and transport costs militate against the use of urban compost on arable land. The main market is seen in landscaping but also home gardening provided the compost is free of toxic substances.
A third source of nutrients from biotic residues may derive in EU from meat and bone meal, which till now was a source of protein in animal feeding. With growing concern of using animal protein in beef production in context with the BSE crisis, EU will ban use of animal meal and the agriculture may also be forced to recycle this material, which would become an additional source of nutrients for crop production. In consequence of a possible ban of using meal and bone meal in animal feeding in EU, there would be a deficit of about 200,000 t protein (DLG, 2000). This corresponds to about 500,000 t soybean cake or the equivalent of 30,000 t N, 2,000 t P2O5 and 12,000 t K2O to be imported in addition.
2. Increasing demand for meat - its implication for fertilizer use
2 to 8 kg cereal grain is required to produce one kg meat. In addition to that, large quantities of feed concentrates are used in livestock husbandry.
Only a fraction of nutrients supplied with feed to livestock is removed in animal products sold from the farm. According to Bach et al. (1997), only 22% of N and P, and 4% of K are attached to animal products, the bulk of nutrients remain at the farm in form of animal excrements. Consequently, the share of organic manure in total nutrient input increases with livestock. On average in the European Union, EFMA calculates that about 30% of total N use, almost 50% of P2O5 and more than 60% of K2O derive from livestock. Furthermore, the nutrient balance tends to become more positive with increasing livestock intensity. Arable farms in Germany for instance have a farm gate nutrient balance almost in equilibrium, whereas typical livestock farms show a surplus of 166 kg N/ha, 48 kg/ha P2O5 and 82 kg/ha K2O (figure 4). Correspondingly, typical dairy farms in Belgium show a highly positive nutrient balance although use of mineral fertilizer decreases, because of increasing input of nutrients with feed concentrate (Michiels et al., 1997).
On the other hand, a falling livestock population as observed in East Europe, lack of affordable labor to apply organic manure in East Asia, or simply misuse of farmyard manure as fuel and building material as in India, Pakistan or Africa, decreases the availability of nutrients from livestock. At the same time, this increases the need to supplement the crops' nutrient demand with mineral fertilizers. In China for instance, the share of nutrients from organic manure fell from almost 100% in 1949 to currently about 30% (Asiafab, 2000).
| Figure 4: Nutrient balance as affected by the farming
system example Germany |
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| Bach et al, 1997 |
The international trade in livestock feed concentrate also implies a considerable transfer of nutrients. Taking only oilseed cake and seeds into account, it shows that the European Union imported in 1997 the equivalent of 574,000 t K2O, which adds to the potash balance in EU. Japan alone imported the equivalent of 142,000 t K2O with feed concentrate. Major 'suppliers' of potassium contained in oilseed cake and seeds were Brazil (335,000 t K2O), Argentina (211,000 t K2O) but also India with 73,000 t K2O. Interestingly, the 'export' of 211,000 t K2O with feed concentrate from Argentina is 7 times the amount of K2O that Argentina imports with potash fertilizers. In other words, Argentina is exporting a substantial amount of indigenous soil fertility.
3. Change in crop spectrum towards vegetables and oilseed and its impact on nutrient management
More vegetables and fruits in the diet as income increases and more oilseeds to feed beef cattle affect the cropping pattern and thus the nutrient management.
In China for instance, the area under vegetables increased in the last 30 years 4 times and the area with fruits even 8 times. In contrast, the area with oil crops increased slightly by 50%, whereas the area with cereals even decreased (figure 5).
| Figure 5: Crop spectrum in China as affected by changes in diet |
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| database FAOSTAT '98 |
A comparable trend is seen in California, USA where the share of field crops in the acreage decreased in the last 20 years from 72 to 55%. Correspondingly, the share of vegetables and fruits together increased from 28 to 45%. More instructive is the change of crop value with time. At a comparable total acreage, the total crop value increased from $9.28 billion to $16.6 billion. This is primarily caused by the added value of vegetables and fruits of $7.65 billion whilst the value of field crops even decreased by $0.34 billion (figure 6).
| Figure 6: Change in harvested area and crop value in California |
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| from Johnston & Carter, 2000 |
Concerning oilseeds, the global area of soybean trebled in the last 40 years from 24 million ha in 1961 to currently more than 70 million ha. Most of the acreage was added in Argentina and Brazil, which increased the area with soybean from almost nil 40 years ago to currently 7 and 13 million ha, respectively.
Some of the consequences for nutrient management, as derived from the changes in crop spectrum, can be summarized as follows:
- Fruits and vegetables remove considerably more nutrients from the field than cereal grains (figure 7). The transferred nutrients have to be replaced to close the balance.
| Figure 7: Nutrient removal by crops, vegetables and fruits in comparison to cereals |
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| after Shrotriya, 2000 |
- Oilseeds have a particular requirement for potassium. The K content in soybean seeds is about 5 times higher than that in cereal grains. The poor root system of soybean has a specific high demand on K concentration in soil solution. In return, adequate supply of potash to soybean and other leguminous crops improves nodulation and therefore biological nitrogen fixation. Sunflower absorbs over the growing period up to 500 kg/ha K2O, winter oilseed rape up to 400 kg/ha K2O. This implies a rather high daily K uptake intensity and thus K supply through fertilizers.
- The rather short vegetation period and the rapid biomass development of vegetables on the one hand and the rather poor root system on the other require a much higher soil nutrient release intensity and a higher soil nutrient concentration than necessary for cereals (figure 8). This requires split application, especially on light textured soils and additional fertilizer nutrients on heavy soils to overcome fixation and/or interference in the absorption complex of the soil.
| Figure 8: Soil K concentration needed in soil solution to sustain an uptake rate of 5 kg K per ha as affected by root length density |
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| after Johnston et al, 1998 |
- Micro-irrigation, together with fertigation of field grown and protected vegetables, is now common practice. Nutrient management has to consider aspects such as:
- the daily nutrient uptake and nutrient requirement of the crop,
- the NK ratio in nutrient supply to meet the physiological requirement of the crop, which needs a N-oriented nutrient ratio during the vegetative stage and a K-oriented nutrient ratio during fruit development,
- the compatibility of fertilizer nutrients in the liquid phase (precipitation),
- the concentration of the stock solution (salting out),
- the concentration of the irrigation water (osmotic effects in the rhizosphere).
4. Focus on quality necessitates balanced fertilization
Quality is an 'intrinsic property of food by which it meets predefined standard requirements. Determinants of food quality can be grouped into several properties. Food quality therefore refers to the value, which is subjectively or objectively attached to food with respect to quality properties' (Abalaka, 1999).
The following properties can be distinguished:
- Nutritional properties: numerous field trials conducted by IPI and other fertilizer associations have shown that balanced fertilization increases for instance the protein content in wheat, oil content in soybean, groundnut and rape seed or the vitamin C content in vegetables and fruits (figure 9).
- Functional properties: this refers for instance to sugar content in beet and cane, fiber content and quality in cotton, flax, jute, starch content in potato, etc. Balanced fertilization has a quality improving effect on these traits as well (figure 10).
- Organoleptic properties: this is related to taste and appearance. Balanced fertilization for instance increases the content of aromatic compounds in tea and thus the quality (figure 11).
- Hygienic properties: plants adequately supplied with potash show reduced incidence of pests and diseases (figure 12). Reduced disease eases compliance with sanitary and phytosanitary regulation in international trade. Better crop resistance to pests and diseases would also reduce the input of agrochemicals and thus minimize the concern on residual effects.
- Environmental compatibility: consumers will ask more than before whether the crop has been produced under environmentally friendly practice. The substantial decrease of residual N with balanced fertilization, as observed in IPI trials in China, is a step towards the required environmental compatibility of crop production (figure 13).
- Safe food: in an atmosphere of uncertainties on food safety such as nitrate content of vegetables, residues of agrochemicals, beef and BSE, quality auditing of production could bring back confidence of consumers. And, balanced fertilization in an integrated approach is one of the most important components in quality auditing. It also adds a particular image to the produce, the added value increases the competitiveness. Moerschner et al. (1999) see a good market opportunity for those farmers, who adopt management systems with respect to quality and environment.
Conclusion
Fertilizer use is one of the 4 major investments in agriculture to increase production in accordance to the overall population growth and the specific needs of urban societies. The other major investments are irrigation, seed protection and biotechnology. In contrast to rural communities where most of the nutrients contained in food are recycled, feeding of urban communities is in principle a one-way traffic for nutrients. Recycling of nutrients consumed in urban centers emerges only now. This implies on the one hand an increasing need to replenish those nutrients exported into towns. This also needs the knowledge on how to apply fertilizers to produce more food. On the other hand, it must be considered how best to integrate those nutrients coming back in future from the towns into the nutrient management. Bulkiness of the nutrient carrier and thus higher transport costs, undesirable accompanying substances and thus product liability, will be some of the problems, which confront agriculture in the context of urbanization. Nevertheless, agriculture will be more than ever forced to recycle urban waste, which affects the nutrient balance and thus fertilizer use.
Farmers have also to take account of the changing food habits and the focus on quality of the urban population. Most consumers rate quality as the most important determinant of acceptability of goods in the market. Balanced fertilization is an important step to meet the demand. The fertilizer industry should also take the challenge and provide the farmers with the necessary input and knowledge. To adjust production to verifiable quality norms would not only secure old and open new markets for the farmers, it would also indirectly contribute to a positive image of the fertilizer industry, provided the industry would be in the position to assist the farmers accordingly. The benefits for the farmers when using balanced fertilization in an integrated approach are clear: they can certify quality and origin of their produce, they prove compliance with legislative rules and will not have problems with product liability.
References
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