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Presented at the RICP-CISTA-IPI-IMPHOS Workshop on:
Balanced fertilization for crop yield and quality
17-19 September 2001, Prague, Czech Republic
Global and regional potash consumption and deriving K balance in agriculture
by 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;
www: www.ipipotash.org
Contents
Growing demand for more and better food challenges crop production
and fertilization
Higher productivity of cultivated land removes more nutrients
from the soil and drives fertilizer demand
Global fertilizer consumption continues to grow
Nutrient ratio in fertilizer use becomes increasingly unbalanced
to the expenses of potassium
Regional potash use often covers only a fraction of K removal
by crops
Can organic manure compensate the gap in K supply?
Extended soil K mining at unbalanced fertilization deteriorates
soil fertility, lowers the profit of farming, decreases use efficiency of
natural resources and is a threat to the environment
Conclusion
References
Growing demand for more and better food challenges crop production and fertilization
Global population increases annually by about 80 million and will hit the 8 billion mark within the next 20 years. Most of the population growth will occur in developing countries where, between now and the year 2020, the population will increase by additional 1.5 billion inhabitants to reach 6.3 billion in 2020 and even 8 billion in fifty years from now. Furthermore, FAO (2001) estimates that by, the year 2030, the proportion of the world's population living in towns will have grown to 61% compared with 40% in the 80ies and 48% today. The increase in urbanization will be greatest also in developing countries (1980 < 30%, 1999 40%, 2030 57%).
| Fig. 1. Evolution of global cereal production |
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| data source: FAO, 2001 |
More people need more food. ROSEGRANT et al. (1995) calculated that the global demand for cereals will increase till 2020 by almost 1 billion t to 2.7 billion t, and for meat by 75% to 283 million tons. Taking losses at storage and conversion into account, the world agriculture should produce by 2020 about 3.4 billion t cereals. In addition to that, with increasing income, consumers demand more animal protein, fruits and vegetables. Quality becomes an important parameter in selecting the food. And last but not least, consumers look more than before whether food is safe and has been produced in context with conserving the environment.
Most of the required higher crop production has to come from increased yield because land reserves for cropping become progressively scarce due to competition for urban settlements, industrialisation, civic needs, etc. Figure 1 shows indeed that, during the last 40 years, the increase in production of cereals derived mostly from higher yield because the area with cereals remained at almost the same level. For the future crop production towards the year 2030, FAO estimates that, for instance in South Asia, yield increases will contribute 83% to higher production, increase in cropping intensity 12% and arable land expansion merely 5% (SINGH, 2001).
Higher productivity of cultivated land removes more nutrients from the soil and drives fertilizer demand
It has been repeatedly proved that use of mineral fertilizer contribute 30 - 40% to yield increases. On global average, 1 kg NPK increases cereal yield by about 10 kg grains. On the other hand, the global mean yield of 3 t/ha cereal removes 50-80 kg/ha N, 25-35 kg/ha P2O5 and 15-90 kg /ha K2O, depending whether the grains only are harvested or the whole plant including straw. The higher the yield the larger becomes nutrient removal by crops.
| Fig. 2. Regional K removal by crops |
 |
| data source: FAO, 2001 |
The global nutrient removal by crops almost doubled in the last 30 years from about 40 million t (Mt) of N, 20 Mt P2O5 and 35 Mt K2O in 1970 to currently 75 Mt N, 35 Mt P2O5 and 70 Mt K2O. This compares with the current fertilizer consumption of 81.7 Mt N, 32.2 Mt P2O5 and 21.9 Mt K2O (2000/01).
Figure 2 shows the evolution of the global K removal by crops. Most of the K removal by crops occurs in developing countries. This also indicates a rapid increase in crop production. For instance, cereal production in developing countries more than doubled from 580 Mt 30 years ago to currently 1.23 billion tons. Similarly, production of root and tuber crops, known for their K demand and removal, increased in developing countries by 60%.
Global fertilizer consumption continues to grow
The global fertilizer consumption grew vigorously till end of the 80's (figure 3). The growth came to a halt end of the 80's with the economic reform in the area of the former COMECON due to the financial crisis in agriculture, missing market structures, unclear land titles, etc. Fertilizer use in Western Europe also dropped but caused by set-a-site programs, economic and ecological considerations.
| Fig. 3. Evolution of the global fertilizer consumption and the deriving NK ratio in nutrient use |
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| FAO, 2001 |
The global fertilizer consumption recovered in the mid-nineties, the use of nitrogen in particular. IFA (2001) expects that the current use of 81.7 Mt N will increase further to about 93 Mt in 2005/06. Consumption of phosphate is expected to increase by another 6.7 Mt to 38.9 Mt P2O5 and potash by 3.2 Mt to 25.1 Mt K2O in 2005/06. Interestingly, even with the further increase in consumption, the global potash use of 25.1 Mt K2O as forecasted for 2005/06 will be still below the peak of 28 Mt K2O as achieved during 1988/89.
| Fig. 4. Evolution of regional K use |
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| FAO, 2001 |
As indicated earlier, fertilizer use in developed countries suffered from a considerable setback in the late 80's. NPK consumption dropped from more than 80 Mt NPK to currently about 50 Mt and remained at this level in the last 6 years. P and K in particular suffered most. K consumption decreased to half of what was used in the late eighties (figure 4). N consumption in developed countries declined only by 30%. In contrast, fertilizer use in developing countries shows a continuous growth, also in potash. 20 years ago, developing countries shared only about 16% of the global K use or about 4 Mt K2O. It rapidly increased its share to currently 51% or about 11 Mt K2O.
Nutrient ratio in fertilizer use becomes increasingly unbalanced to the expenses of potassium
As shown in figure 3, the NK ratio in global fertilizer use deteriorated in the last 20 years from a fairly balanced ratio of 0.4 towards a more unbalanced ratio of 0.26 and will obviously remain at this level according to the fertilizer forecast. There are considerable regional differences in the NK ratio of fertilizer use (figure 5). Developing countries in general have a less balanced NK ratio in fertilizer use (NK = 0.21) than developed countries (NK = 0.37). Asia is still using highly unbalanced fertilization, which contrasts sharply with the ratio at which plants absorb N and K.
| Fig. 5. Regional NK ratio in fertilizer use as compared to nutrient uptake by crops |
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| data source: FAO, 2001; KEMMLER & HOBT, 1985 |
Regional potash use often covers only a fraction of K removal by crops
Regional K use ranges from about 32 kg/ha K2O in Western Europe to 1-3 kg/ha in FSU, West Asia or Sub-Saharan Africa (figure 6). In Europe, Ireland and Belgium lead with almost 110 kg/ha K2O, followed by Switzerland (81 kg/ha) and Belarus (78 kg/ha K2O). Russia occupies the end of the range of European countries with 2 kg/ha, followed by Romania with 1 and Albania with 0.1 kg/ha K2O (mean 1997-99).
Figure 6 also shows that the regional K removal by crops exceeds by far potash use. The apparent K balance (potash use minus K removal by crops) gives for developing countries a deficit of about 48 kg/ha K2O, mostly caused by huge deficits in East and Southern Asia of 81 and 47 kg /ha K2O, respectively. On average, potash use in developing countries covers only 20% of K removal by crops. The K balance in developed countries became also negative with an average of 6 kg/ha K2O, the deficit in Central/Eastern Europe is about 14 kg/ha and in Western Europe 4 kg/ha K2O. Potash use in developed countries covers about 73% of the K removal by crops.
| Fig. 6. Regional K use (kg/ha K2O) in comparison
to the corresponding K removal by crops (values: mean 1997-99). |
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| data source: FAO, 2001 |
The regional balance for N and P is less dramatic than for K. On principle, use of nitrogenous fertilizers is in developed and developing countries in the same order of magnitude as N removal by crops. The same applies to Western Europe, whereas N use in Central/Eastern Europe and especially in the Former Soviet Union (FSU) is 15 and 40% below N removal. Phosphate use holds an intermediate position with rather good coverage of P removal in both groups, developed and developing countries, but with a considerable deficit in CEE and FSU.
| Fig. 7. Evolution of K and N balances in developed and developing countries |
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| data source: FAO, 2001 |
The evolution of the K balance over time in developed and developing countries is rather different (figure 7). Up to the end of the eighties, the K balance in crop production of developed countries including CEE and FSU was positive, i.e. farmers applied more K in form of potash than K was removed by crops. This indicates build-up of soil fertility. The situation reversed during the early nineties, especially as mentioned earlier when fertilizer use in CEE and FSU, but also in WE, was considerably reduced. Crop yields were still high and so was K removal by crops. Consequently, the K balance in developed countries eventually became negative, soil K mining started.
The K balance in developing countries was negative from the beginning. The gap between potash use and K removal by crops, which reached a deficit of about 45 million t K2O (1997-99), increases annually by another 825'000 t K2O. Region-wise, the current K balance of West Asia is -2.7 Mt K2O, in South Asia -9.6 Mt K2O and in East Asia incl. China -19.1 Mt or, as mentioned, -81 kg/ha K2O. Common to all developing countries or regions is that the deficit in K is steadily increasing.
In contrast to potassium, the N balance in developing countries, although negative at the beginning, becomes progressively more positive in the course of time. This again signals the steadily growing imbalance of fertilizer use in developing countries and thus, increasing loss of soil fertility. The N balance in developed countries runs parallel with the K balance albeit it remained positive throughout the time (figure 7).
Can organic manure compensate the gap in K supply?
China is a classical example for recycling nutrients with organic manure and waste. However, although the total quantity of organic manure increased almost four times in the last 50 years, the share of nutrients from organic source declined from 100% in the 50's to currently 30%. Even when utilizing all possible organic sources, the countrywide K deficit in fertilization is estimated at about 8 Mt K2O (KRAUSS & JIN JIYUN, 2000).
Detailed investigations in India also showed that utilization of all potential organic manure and waste would not be enough to close the gap in the K balance. As an example, the State of Uttar Pradesh, which has the largest area of cultivated land in India, has a potential of 276'000 t K contained in farmyard manure FYM and 194'000 t K in crop residues (YADAV et al., 2001). The total K removal by crop is estimated at 1.78 Mt K. Adding to 777'000 t K applied with potash the K from FYM and crop residues, the deficit would still be 530'000 t K alone in this State. But fact is that more than half of available FYM is misused as fuel due to missing alternative source of energy. The K deficit of whole India is about 7 Mt K2O even when taking all possible K sources, organic and inorganic, into account (BANSAL, 1999).
Sub-Saharan Africa's harvest including residues removes, according to STOORVOGEL & SMALING (1990), some 4.1 Mt N, 2.1 Mt P2O5 and 4.25 M t K2O annually. Mineral fertilizers cover about 37% of N removed by crops, 42% of P2O5 and 9% of K2O. Use of farmyard manure covers much less, namely 6% of N removal, 7% of P2O5 and 16% of K2O. This means that organic manure is not in the position to close the gap between nutrient removal and use of mineral fertilizers, soil nutrient mining continues at a high rate.
| Fig. 8. K balance in Czech Republic |
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| after MACHALEK et al., 2001 |
In Central/Eastern Europe, CEE like in Czech Republic, farmyard manure became the major source of nutrient input after the collapse in use of mineral fertilizers end of the 80's. As shown in figure 8 for potassium, use of potash fertilizers decreased drastically by almost 90% in the post-reform period. But also the K input with organic manure (composts, slurries, FYM) decreased from nearly 40 kg/ha K in the pre-reform period (1986-90) to nearly 20 kg/ha K during the last years (1996-99). This is caused by a considerable decline in the number of cattle, which decreased from 1993 by 1 million to 1.57 million in 2000 and the number of pigs from 4.6 to 3.69 million heads (FAO, 2001). Consequently, the K balance changed from a surplus situation before the economic reform (+40 kg/ha K) to a deficit one with -9 kg/ha K (MACHALEK et al., 2001).
| Fig. 9. Nutrient balances of farms in Germany as affected by the livestock intensity |
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| after BACH et al., 1997 |
The K balance of farms in Germany differs with the farm type. As a general observation, the balance for all 3 major nutrients becomes more positive with increasing intensity of livestock (figure 9). Arable farms tend to be deficient in K, the K balance is negative because of decreasing use of potash. Although livestock farms apply less potash as well, the K balance is positive because of increasing input of K with feed concentrate in form of oilseed cake/meal, etc. The same applies to the other major nutrients, N and P2O5. In this context, it is interesting to see that the European Union (EU) "imports" about 600'000 t K2O annually with oilseed cake/seeds, mostly from Argentina and Brazil. Most of K, taken up by animals with fodder, remains in form of excrements at the farm (96%), only 4% of total K is exported with the animal product, e.g. contained in milk and meat. The corresponding figure for N and P2O5 is 78% each in excrements and 22 % of total N and P leaves the farm with sold products (BACH et al., 1997). Farmyard manure and slurries play indeed an important role in the nutrient supply of farms in EU. EFMA (2000) estimates that, from the total nutrient input in EU, about 30% of N, 50% of P2O5 and 60% of K2O derives from livestock.
Extended soil K mining at unbalanced fertilization deteriorates soil fertility, lowers the profit of farming, decreases use efficiency of natural resources and is a threat to the environment
| Fig. 10. Content of soil K as affected by cropping intensity |
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| after CHENG MINGFANG et al.,1999 |
In principle, negative nutrient balances run parallel with declining soil nutrient contents. In Hungary for example, potash consumption decreased from as much as 449'000 t K2O in 1988/89 to currently (1999/00) less than a tenth, namely 40'000 t K2O (FAO, 2001). Consequently, the share of soils having a good to very good K status decreased from 75% in 1987-90 to 48% in 1994-98. Correspondingly, the share of soils low and poor in K increased from 25 to 52% (BUZAS & LOCH, 2001).
| Fig. 11. Impact of long-term K supply (1970-97) on opportunity yield of different crop types |
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| after MERBACH et al., 1999 |
However, soil K mining is often undetected by routine soil analyses. CHENG MINGFANG et al. (1999) demonstrated that, in Northern China, the content of exchangeable soil K remained almost constant irrespective to the cropping intensity and thus soil K mining, whereas the content of non-exchangeable K substantially decreased (Figure 10). At the same time, the release rate of exchangeable K declined from almost 10 mg K per kg soil per minute to less than 5 mg K. The K release from the non-exchangeable fraction is much lower and decreased from 0.5 mg K/kg/min to 0.1 mg K. Simultaneously, K adsorption of the same soils trebled from 600 mg K/kg soil at low cropping intensity to more than 1800 mg K/kg soil at high intensity. These soils possess obviously a fairly good replenishment of exchangeable K from the non-exchangeable fraction, which maintains the status of readily available K and masks the real K loss. However, the more the plant depends on K release from the non-exchangeable fraction, the lower is the yield as shown by GRIMME (1974).
| Fig. 12. Quality and yield of sugar beet as affected by the balance in nutrition |
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| IPI trials in Hungary, 2000 |
With consecutive soil K mining, the yield gets lower. But the response to soil K mining differs with crop type. A long-term field trial of MERBACH and co-workers (1999) in Germany showed that leafy crops like potato and sugar beet lost almost 40% of opportunity yield whereas wheat maintained the yield level despite of omitting the K supply to the soil for almost 30 years (figure 11). Legumes such as peas as well as barley showed an intermediate reaction.
Having almost 40% less yield at inadequate K supply with the same NP input than at sufficient K also indicates a considerably reduced NP fertilizer use efficiency. This also means that much more NP remains under-utilized in the soil at K deficiency and thus, prone to be leached, eroded, volatilized or otherwise lost to the environment.
One of the reasons of crop specific response to declining soil K status can be seen in the root length density. Cereals have a higher root length density than leafy crops such as potato or sugar beet. This implies a better root-soil K interception. Accordingly, JOHNSTON and co-workers (1998) found an inverse relationship between root length density and necessary solute K concentration in order to sustain a certain daily uptake rate of potassium.
Concerning the economic loss at unbalanced fertilization, IPI trials in CEE showed that sugar beet growers in Czech Rep., Hungary or Poland loose opportunity yield worth $76-300 per ha by not applying potash. Potato growers in Poland or Romania lost crop value of $140-590 per ha, rape seed growers in Czech Republic about $590 and grape growers in Bulgaria lost even $800/ha at unbalanced NP fertilization. The damage to the national economy is even higher taking into consideration for instance the higher transport and extraction costs of beet low in sugar content when cultivated at unbalanced fertilization (figure 12). Furthermore, poor quality of crops at unbalanced NP fertilization lowers the competitiveness at the market.
Further economic losses occur when plants are more susceptible to pests and diseases. Lower yield with inferior quality, together with higher input costs for pest and disease control, reduce the economy of fertilizer use at unbalanced nutrition. The same applies to the tolerance of crops to climatic and soil borne stress. WYRWA and co-workers (1998) showed that K deficient triticale lost more than 60% yield at drought, whereas triticale grown under adequate K supply yielded only 17% less than plants not subjected to drought.
Conclusion
The function of soils to buffer the K supply bears the risk to mask the true K status. Farmers, especially in developing countries, often overestimate the K supply capacity of their soils. Misinterpretation of soil test results and blanked fertilizer recommendations are other reasons of inadequate K supply. Furthermore, farmers tend to rely too much on the visible response of their crop. And naturally, use of N fertilizers shows an immediate effect on the crop stand. K in contrast acts more 'discreetly' than N and often the response will not be recognisable until the crop is harvested. Lastly, inferior crop quality or higher susceptibility to pests, diseases and climatic stress are seldom seen in context with unbalanced or inadequate K fertilization. In consequence, K usually gets a low priority when planning fertilizer use especially in times of economic constraints as happens in Central/Eastern Europe, the FSU or in developing countries.
On the other hand, there is need to produce more and better food and fibre without damaging the environment. It is no longer acceptable to have N use efficiencies in the range of 30-50%, meaning that from the global N consumption of 85 Mt, about 40 to 60 Mt N are lost to the environment. There are numerous results available on the positive effect of balanced fertilization with adequate K on safeguarding the environment, both directly and indirectly. Better crop stand at balanced fertilization and better soil anchorage and thus, reduced nutrient losses through erosion affect directly, higher yields at balanced fertilization and thus better N fertilizer use efficiency affect more indirectly the environment. The main problem is to educate the farmers and inform policy makers on the relationship between balanced fertilization and its impact on food security and environment protection.
In this respect, scientists and researchers in soil fertility together with the advisory service, both the public and the private service such as IPI, have to co-ordinate and strengthen their efforts to create more knowledge through field trials or lab experiments. As important is to transfer the knowledge to the concerned persons, the farmer, extension agent, fertilizer dealer or the policy maker.
References
Bach, M., Frede, H.G. and Lang, G. (1997): Entwicklung der Stickstoff-, Phosphor- und Kalium-Bilanz der Landwirtschaft in der Bundesrepublik Deutschland. Gesellschaft für Boden- und Gewässerschutz eV., D-35435 Wettenberg.
Bansal, S.K. (1999): personal communication. Potash Research Institute of India, PRII, Gurgaon, Haryana, India.
Buzas, I. and Loch, J. (2001): Development of potash fertilizer input and the consequences for soil fertility and crop production in Hungary (in Hungarian with English summary and captions). Country Report 2 'Hungary', Int. Potash Institute Basel, Switzerland, 63 pages.
Cheng Mingfang, Jin Jiyun and Huang Shaowen (1999): Release of native and non-exchangeable soil potassium and adsorption in selected soils of North China. Better Crops International, Vol. 13 (2), pp.3-5.
EFMA (2000): European Fertilizer Manufacturers Association, Brussels, Belgium. Pers. communication.
FAO (2001): Food and Agriculture Organization Rome, Italy, website.
Grimme, H. (1974): Potassium release in relation to crop production. In: Proc. 10th Congress Intern. Potash Institute, Budapest, Hungary, pp. 131-136.
Johnston, A.E., Barraclough, P.B., Poulton, P.R. and Dawson, C.J. (1998): Assessment of some spatially variable factors limiting crop yield. Proceedings No. 419, The International Fertiliser Society, York, UK.
Kemmler, G., and Hobt, H. (1985): Potash a product of nature. K+S Kassel, Germany, 112 pages.
Krauss, A. and Jin Jiyun (2000): Strategies for improving balanced fertilization. IFA Production and International Trade Conference, 17-19 October 2000, Shanghai, China.
Machalek, V., Cermak, P. and Klir, J. (2001): Development of potash fertilizer input and the consequences for soil fertility and crop production in the Czech Republic. IPI Country Report Series 2 (in print).
Merbach, W., Schmidt, L. and Wittenmayer, L. (1999): Die Dauerdüngungsversuche in Halle (Saale). B.G. Teubner, Stuttgart-Leipzig, pp. 56-65.
Rosegrant, M.W., Agcaoili-Sombilla, M. and Perez, N.D. (1995): Global food projections to 2020: Implications for investment. Food, agriculture, and the environment, Discussion paper 5, International Food Policy Research Institute.
Singh, R.B. (2001): The state of food and agriculture in Asia and the Pacific: challenges and opportunities. 69th IFA Annual Conference, 21-24 May 2001, Sydney, Australia.
Stoorvogel, J.J. and Smaling, E.M.A. (1990): Assessment of soil nutrient depletion in Sub-Saharan Africa: 1983-2000. The Winand Staring Centre Wageningen, The Netherlands, Report 28.
Wyrwa, P., Diatta, J.B. and Grzebisz, W. (1998): Spring triticale reaction to simulated drought and potassium fertilization. In: Proc. 11th Int. Symposium on Codes of good fertilizer practice and balanced fertilization, Pulawy, Poland, September 27-29, pp. 255-259.
Yadav, R.L., Dwivedi, B.S., Singh, V.K. and Shukla, A.K. (2001): Nutrient mining and apparent balances in different agro-climatic zones of Uttar Pradesh. Fertiliser News 46 (4), 13-31.