international fertilizer correspondent
No 6
international fertilizer correspondent No 6 |
|
Urban influenceFew can be unaware of the fact that the global population is rising. Even more obvious from our day-to-day experience is that ever greater numbers of people are moving from their rural homes to seek work in towns and cities. In developed countries, 75% of the population already lives in an urban setting. In developing countries the percentage is expected to rise from 40% to 50% within the next two decades. All these people need food. Almost all of that food will be produced far from the city centres and too far for the economic return of waste products. What will be the effect of this urban migration of soil nutrients? What should farmers, city planners - and the fertilizer industry - be doing about it?
The city of Isfahan in Iran is growing fast and its food requi-rement is expected to increase by 7 Mt to 20 Mt within the next ten years. Karachi, Pakistan, will need another 20 Mt of food on top of its current 44 Mt. Assuming that 80% of the diet is based on cereals, the future food demand for Karachi would contain almost 1 Mt N, 0.4 Mt P2O5 and 0.25 Mt K2O. The pattern is repeated throughout the world. And remember that urban populations eat differently from their country cousins. Admittedly the urban majority in developing countries are on low incomes and have to satisfy their hunger with low value subsistence food such as cereals and tuber crops. As incomes rise, diets change towards more animal protein and more vegetables and fruit. The link between income and food habits is clearly illustrated in China. Urban people eat more meat (27 kg per capita) and less rice (68 kg per capita) per year than their rural counterparts who consume 17 kg of meat and 103 kg of cereals. The per capita supply of vegetables in wealthy Asian countries, such as Japan, is more than double that in developing countries whose citizens consume, on average, 45 kg of vegetables per capita per year.
Quality and convenience become increasingly important issues to people living in towns and, eventually, the wealthiest societies choose pre-packed and table-ready processed food. Fear of high nitrate levels in vegetables, growth hormones and antibiotics in meat, BSE and, in Europe, foot and mouth disease, also influence their shopping patterns. There is, therefore, increasing interest in ‘safe’ food of ‘bio’ origin and, although the market share of organic food is still small, it is growing fast. ‘Functional’ food is also coming into the picture of changing food habits. Functional food has specific health promoting cha-racteristics. Lycopene in tomato, allicin in garlic or isoflavones in soybean, for example, are associated with prevention or treat-ment of cancer, diabetes, hypertension and heart disease. Another example is the rice that has been genetically modified to synthesize and accumulate beta-carotene (provitamin A) or to contain three times the iron content of conventional rice, factors involved in controlling eyesight and anaemia respectively. What are the consequences for fertilizer use and nutrient management from the changes in food habits brought about by urbanization?
Globally about 175 Mt N + P2O5 + K2O are removed annually with harvested crops. Assuming that 47.5% of the world’s population live in cities, this means that at least 83 Mt NPK nutrients are lost annually from the agricultural land on which the crops were grown and from which, of course, subsequent crops must be produced. It is also reasonable to estimate that at least half of Asia’s total vegetable production of 402 Mt is consumed in towns. This represents the transfer of about 1.8 Mt N, 0.4 Mt P2O5 and 0.6 Mt K2O. The nutrients excreted after digesting the food are deposited in urban dumping sites which is where they remain. Admittedly in some countries there is pressure on farmers to use sludge from urban water treatment plants but estimates from the European Fertiliser Manufacturers’ Association (EFMA) indicate that only about 2.6% N, 3.5% P2O5 and 1.1% K2O used in EU agriculture derive from non-livestock urban waste. This is despite incentives to farmers who can claim subsidies and other forms of support if they use the waste material.
Meat and bone meal, until now a source of protein in animal feeding, may become available as an additional source of nutrients for crop production as a consequence of EU legislation following the BSE crisis. But a ban on the use of animal protein for feeding to livestock would create a deficit of about 200,000 t protein in the EU. 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 which would have to be imported.
Most nutrients supplied with feed to livestock remain on the farm in the form of animal excrement. The nutrient balance therefore tends to become more positive with increasing livestock intensity. EFMA calculates that about 30% of N, almost 50% of P2O5 and 60% of K2O total use in the EU derive from livestock. In Germany, for example, the farmgate nutrient balances on arable farms, are almost in equilibrium whereas typical livestock farms show a surplus of 166 kg N/ha, 48 kg/ha P2O5 and 82 kg/ha K2O. Nutrients brought on farm through feed concentrate lower the requirement for mineral fertilizers. A similar trend is also seen in ‘organic’ livestock farms partly because nutrient output with animal products is low but also because farmyard manure is recycled and N-fixing crops are grown. On organic arable farms without livestock, nutrients will be ‘exported’ with the sold crop, quickly tipping the nutrient balance into the negative for K and P. Unless the correct action is taken, the long term consequences of the trend towards organic production could be too great an accumulation of N on farms where livestock are kept and too great a loss of K and P on farms where they are not.
Replacing lost nutrients with farmyard manure is a challenge that goes beyond consideration of logistics and cost. In Eastern Europe, for example, fewer livestock are being raised, reducing the availability of farmyard manure. In East Asia it is the lack of affordable labour to apply organic manure that limits its use. In India, Pakistan and many African countries, farmyard manure is used as fuel and building material, denying its use for replacing soil nutrients. This increases the need to supplement the crops’ nutrient demand with mineral fertilizers.
International trade in feed concentrates transfers considerable quantities of nutrients from one part of the world to another. Taking only oilseed cake and seeds into account, the EU imported the equivalent of 574,000 t K2O in 1997 and Japan alone imported the equivalent of 142,000 t K2O. Major supplier countries were Brazil (335,000 t K2O), Argentina (211,000 t K2O) and India (73,000 t K2O). Interestingly, Argentina’s exports of K2O in feed concentrate are seven times the amount imported as potash fertilizer.
| Nutrient removal by crops |
|---|
 |
| after KEMLER AND HOBT, 1985 |
As food production changes to meet the changing demand from consumers, nutrient management must also change to meet the demands of the crop. Furthermore, a trend towards fruit and vegetables, and away from cereals, increases crop value per acre/hectare and justifies a larger spend on inputs. In California, USA, for example, vegetables and fruits have taken over land previously used for lower value field crops and increased the total crop value from US$9.28 billion to US$16.6 billion. The global area under soybean has trebled over the last 40 years from 24 million ha in 1961 to currently more than 70 million ha. These trends alone have important consequences for nutrient management, especially for K.
Fruits and vegetables remove considerable amounts of nutrients from the field. The short vegetation period and the rapid biomass development of vegetables on the one hand, and their rather poor root system on the other, require a much higher soil nutrient release intensity and a higher soil nutrient concentration than is necessary for cereals. This requires split application, especially on light textured soils and additional fertilizer nutrients on heavy soils to overcome fixation and/or interference of the absorption complex of the soil. Micro-irrigation and fertigation make special demands on nutrient management which has to take into account the daily nutrient uptake and nutrient requirement of the crop. For example, vegetables require an N-oriented nutrient ratio during their vegetative growth stage and a K-oriented nutrient ratio during fruit development and ripening.
Oilseeds have a particular requirement for potassium. The K content in soybean seeds is five times that of cereal grains and satisfying this need, especially taking the plant’s poor root system into account, requires a high concentration of K in soil solution. When potash supply to soybean and other leguminous crops is adequate, nodulation and therefore biological N-fixation improves.
| Fertilizing soybean with potash improves nodulation and root development |
|---|
0kg K2O/ha: less developed root system fewer nodules |
 |
 |
| 50kg K2O/ha: more developed root system more nodules |
The urban-induced trends towards more fruit and vegetables and more meat make their own demands upon nutrient management but what will be the effect of increasing consumer demand for ‘safe’ and ‘quality’ food? (See also ifc5) Nutritional and toxicological comparisons between organic and conventionally grown food show that there is no consistent trend of differences for most nutrients and contaminants nor, in reality, are there any sensory differences. The more precise timing of N application with mineral fertilizers on conventional farms tends to produce crops with higher protein, nitrogen and nitrate content. Organically produced wheat flour tends to have a lower baking quality than that produced conventionally. Whatever the advantages or disadvantages of the production method for specific products, the demand for organically produced food will undoubtedly continue to increase making its own special demands on nutrient management. Nevertheless, the vast majority of the world’s population will continue to be sustained from conventionally produced food.
Farmers should be aware that it is not only their sons who migrate to the cities. The soil nutrients that farmers also lose to the urban environment must be replaced if crop production is not to suffer because this one-way traffic in soil fertility is highly damaging. Efforts will have to be made to rethink how best to recycle urban waste back into agriculture. The challenges are to overcome the costs of transporting a bulky, low value material, and to ensure that it contains no harmful substances that could leave the supplier with problems of product liability.
The fertilizer industry should also take up the challenge of urbanization and provide farmers with information on the changing food habits and desire for quality that the urban consumer demands and the inputs that will be required to meet them. To adjust production to verifiable quality standards would not only secure old and open new markets for farmers it would also indirectly contribute to a positive image of the fertilizer industry, provided that the industry is in a position to assist farmers to achieve those standards. The benefits for farmers of using balanced fertilization in an integrated approach are clear; they can certify quality and origin of their produce; they can prove compliance with legislative rules and they will not have problems with product liability. Balanced use of mineral fertilizer will remain the key to safe, cost-effective food production of the quality that the urban population demands.
1) Krauss, A. (2000): Impact of urbanization upon fertilizer usage. Proceed. of 2000 IFA Regional Conference for Asia and the Pacific, 4-7 December 2000, Yokohama, Japan (www.ipipotash.org).
2) Kumpulainen, J. (2001): Nutritional and toxicological quality comparisons between organic and conventionally grown foodstuffs. Proceed. of The 2001 Dahlia Greidinger Symposium/The International Fertiliser Society, 4-6 March 2001, Lisbon, Portugal.
3) Tinker, P.B. (2001): Organic farming – nutrient management and productivity. Proceed. of The 2001 Dahlia Greidinger Symposium/The International Fertiliser Society, 4-6 March 2001, Lisbon, Portugal.
