Over-application is a common problem in Asian countries like Japan, where chemical fertilizer is relatively cheap. The cost of fertilizers is only a small part of total production costs. Farmers want to ensure good yields, and apply so much fertilizer that much of it is wasted. The problem is particularly acute with horticultural crops, which are high-value and produced very intensively in most of Asia. In tropical and sub-tropical climates, provided there is enough soil moisture, vegetable fields may bear as many as ten successive crops a year, all of which may receive heavy applications of fertilizer.
In contrast, other countries in the region have a problem of fertilizer shortages. The cost of fertilizer in such countries is generally high compared to the prices received by the farmer, and fertilizer applications are often well below the recommended levels. Poor timing and poor application technology make this limited use of chemical fertilizer even less effective than it might be.
The rising populations of Asian countries mean that it will be necessary to increase food production. Fertilizer will be an essential part of this process. Since areas of new land are limited, this means mainly intensification on existing agricultural land. Nutrient inputs will have to rise - in fact, it has been estimated they may have to triple! Fertilizer will be an essential part of this process. Asia is moving from agriculture which depends on the natural fertility of the soil, to agriculture which is fertilizer dependent.
Some countries in Asia are already close to the point where additional fertilizer brings no additional yield, or may even be past it. Japan, Korea and Taiwan are all estimated to be applying what is termed the theoretical maximum (theomax). In other countries, however, actual application rates are low, and well below those recommended. Most countries with low fertilizer application rates import most or all of their fertilizer requirements.
As well as average levels of fertilizer consumption per hectare, another way of estimating levels of fertilizer use is to look at the nutrient input/output balance. A study of the nutrient balances for rice and other major crops in selected Asian countries compared the nutrient inputs from fertilizers and other sources, with the amounts removed in the harvested crop and lost in other ways. It found that there was a negative balance for major nutrients (nitrogen, potassium and phosphorus) in several countries, including Indonesia, Myanmar and Vietnam. In Bangladesh and the Philippines, there was a positive balance for nitrogen but a negative one for other nutrients, while Thailand had a negative potassium balance. Negative balances, as with low overall fertilizer application rates, tended to be found in lower income countries with large and growing populations. An oversupply of nutrients is characteristic of higher income countries where population levels are fairly static. The fact of a negative balance has serious implications of a long-term loss of productivity. Countries which are exporting rice and other crops without replacing the plant nutrients they contain are in effect exporting their soil fertility.
Population growth in Asian countries where fertilizer applications are now low means that fertilizer use will almost certainly rise in the future. Higher fertilizer use on a massive scale increases the probability of environmental pollution. There is a danger of environmental damage even where applications are below maximum levels, especially if fertilizer is broadcast onto the soil surface in a single application. The probability increases with rising levels of fertilizer use. We need to find how increased fertilizer use can be sustained with minimum impact on the environment, by e.g. better timing of applications, deep placement, and improved formulations such as slow-release fertilizers.
Fortunately for the future of Asia, the intensification of lowland rice production is likely to be less damaging to the environment than a similar intensification of upland crops would be. In paddy rice production, N and K are both supplied by the paddy ecosystem itself, although not necessarily in sufficient amounts for good yields. Whereas upland soils under continuous monoculture suffer from soilborne diseases and falling yields, paddy soils do not, provided a cycle is maintained between aerobic and anaerobic conditions. Experiments on fertilizers show that upland cereals such as wheat or barley are much more seriously affected than rice by the lack of a particular nutrient element. Asia's staple crop seems to be better suited than most other cereals to be the basis of a high-yielding, sustainable agricultural system.
Most agricultural soils are deficient in N, which can conveniently be supplied in the form of N fertilizer. Because of its low cost and easy transport, there has been a trend towards the use of urea as an N source. However, there is now some doubt whether urea is the best form to use in paddy fields. When urea is used in flooded soils, there are often high losses from denitrification. Improved formulations and application methods may cut down on nitrogen losses. There have recently been interesting developments in coated nitrification inhibitors and other formulations. Correct timing of nitrogen applications is important, to ensure that they coincide with the period of nitrogen uptake by the crop.
Good management of N fertilizer must be accompanied by a concern for the total nutrient balance. Unbalanced use of N in Asia has been considered the biggest factor leading to soil nutrient depletion in Asia. The higher yields made possible with N applications have the effect of removing P, K and other elements in the straw and grain at harvest, to the detriment of subsequent crops.
It has been estimated that one unit of balanced NPK produces from 10 to 30 units or more of harvest. Unbalanced applications, on the other hand, with an oversupply or deficit of some nutrient elements, can have a detrimental effect on crop performance and yield. Even more important, they may have a damaging effect on the long-term productivity of soil. An increasing imbalance of soil nutrients is believed to be a major cause of the stagnation in rice yields observed over recent years in Asian lowland rice paddies.
Several countries are promoting the use of blended fertilizers to help solve this problem. In Fiji, for example, the situation improved rapidly when a domestic fertilizer factory was established which produced blended fertilizers. Sugarcane growers were encouraged to use blended rather than straight fertilizers. However, the use of blended fertilizers may increase fertilizer prices because of the higher handling costs involved. Perhaps a transitional stage is needed, during which blended fertilizers are used, while farmers become accustomed to the principles of a proper nutrient balance for their crops.
Nitrate contamination of groundwater from heavy nitrogen applications is already a problem in some Asian countries, where water in some wells contains nitrate levels that exceed permissible limits. Rice cultivation often uses large amounts of chemical fertilizer. Nitrification is rather an easy process under reduction conditions. If paddy soil is submerged more than ten days, it is unlikely that any nitrate will be released from rice fields into the groundwater. We need to know more about nitrate limits in water, and the effect of nitrogen applications on underground water sources. This is particularly important in Iran, which is largely dependent on underground water sources. Nitrate cannot be removed once it has entered the underground water system.
Direct or dry seeding of rice is becoming increasingly common in Asia, because of its lower labor cost. However, studies on the fate of nitrogen in dry seeding do not seem to show that it causes nitrate leaching. When dry seeding is practiced, the soil is usually flushed with water to germinate the seed and then dried. This is followed by a cycle of drying and flooding over several weeks, during which time the nitrate is lost. By the time the rice field is permanently flooded, no nitrate is left.
It is often proposed that Asian countries should set up a network of soil testing and plant analysis. However, while soil testing is used very effectively in Western countries, both the farms and the fields used for single crops are relatively large. This means that samples from one field represent a large area of land. Farmers are also fairly affluent, and can afford to pay for soil testing. In Asia, on the other hand, farms and fields are small, while the cost of testing soils is high relative to the income of typical small-scale farmers. Is the laboratory analysis system available to farmers in the West the best system for low-income farmers in tropical Asia? Perhaps there are better, more appropriate ways of estimating the fertility status of soils.
Certainly if laboratory tests are to be used for soil and plant tissue samples, the results must be reliable. These analytical results are used as the basis for fertilizer recommendations, in order to supply a sufficient and balanced nutrient supply. If the results are incorrect, so will be the recommended amounts of applied fertilizer. Several studies have found a wide range of variation in test results from standard samples done by different laboratories in different countries. A cross-checking system has been set up by Wageningen University in the Netherlands, but there might perhaps be benefits from a similar regional network. Malaysia already has a national network for monitoring laboratory testing, organized by the Malaysian Soil Science Society.
Even when the problem of accuracy in analysis is solved, there is still great difficulty in applying the results for fertilizer recommendations. This requires a large number of field tests on correlations between fertilizer use and yield. These tests must be repeated for different soils and different crops, or even different varieties of the same crop.
A major problem in appropriate fertilizer use in Asia is an imbalance of applied nutrients. Nitrogen applications tend to be much too high in relation to the amount of potassium and phosphate used. This is partly the result of price differentials, and partly the lack of knowledge among farmers about the need for balanced fertilizer applications.
The use of nitrogen, the main nutrient element in crop growth, tends to be inefficient. A great deal of applied nitrogen is lost by leaching, volatilization and other natural processes. This is not only wasteful, but burdens the natural environment with excessive nitrogen. The problem is particularly marked in paddy fields, since nitrogen losses are high under flooded conditions. However, it is the fertilization of high-value crops such as vegetables with nitrogen which tends to produce much of the nitrate pollution. Nitrate contamination of vegetable crops is a major concern to consumers. Various ways of increasing nitrogen fertilizer efficiency were discussed, including recent developments in coated nitrification inhibitors and other formulations. The most effective way of maximizing the uptake of applied nitrogen by crops is to match N applications with crop needs. This means repeated smaller applications rather than a large single one. Slow release fertilizer formulations and deep placement are also useful, as are cleaning crops to absorb excess nitrogen from the soil.
In some countries the production and/or distribution of fertilizers is under government control, while in other countries one or both of these are in the hands of private companies. Government administration of the fertilizer industry can be costly, especially if backed by direct fertilizer subsidies, but the farm gate price of fertilizers is generally lower, although there may not be a wide choice of products. Governments are also generally more concerned than dealers with the supply of fertilizers to remote areas and low-income farmers, and with balanced use of fertilizers. On the other hand, dealers may be more responsive than governments to local fertilizer requirements and preferences.
Location: Taiwan ROC
Date: November 6-14 1995
No. Participating Countries: 16 (Australia, Bangladesh, Fiji, Hongkong, India, Iran, Japan, Korea, Malaysia, Mongolia,Philippines, Singapore, Sri Lanka, Taiwan ROC, Thailand, US
No. Papers: 19
No. Participants: 120
Co-sponsors: Asian Productivity Organization
Council of Agriculture
Chinese Society of Soil and Fertilizer Sciences
National Taiwan University
Taiwan Agricultural Research Institute.
Keynote Speech: Fertilizer use in Asia: How high can it rise?
2. Efficient use of nitrogen fertilizer by cropsJohn Raymond Freney
3. Country report: Fiji
4. Plant nutrient balances in the Asia and Pacific region: Facts and consequences for agricultural production
Ernst W. Mutert
5. Research achievements in farm management and fertilizer use practices in Taiwan
6. Country Report: Hong Kong
7. Country Report: Bangladesh
8. Country Report: India
Prem Kumar Awasthi
9. Country Report: Iran
Mohammad J. Malakouti
10. Country Report: Japan
11. Country Report: Republic of Korea
12. Country Report: Malaysia (I)
Abdul Aziz Bidin
13. Country Report: Malaysia (II)
Jit Sai Lim
14. Country Report: Mongolia
15. Country Report: Philippines
Francisco C. Cornejo
16. Country Report: Sri Lanka
Anthony Bedgar Perera
17.Country Report: Taiwan ROC
18. Country Report: Thailand
19. Ecological sustainability of the paddy soil-rice system in Asia
Figure 1 Organic Citrus Farm in Taiwan. the Trees Receive Heavy Applications of Composted Manure, Applied in Shallow Trenches Dug between the Trees.
Figure 2 Slurry Applied to Paddy Fields in the off Season, Japan
Figure 3 Modern Compost Factory Processing Cattle Manure from Nearby Farms, Korea