Asia is the world's largest user of chemical fertilizers, consuming 43% of the global total each year. In general, the only Asian farmers who do not use chemical fertilizers are those who cannot afford to buy them. However, some farmers in wealthy countries are practicing organic farming and using no chemicals at all, although this is mainly limited to the temperate countries of Japan and Korea. Experience in tropical Asian countries generally shows that organic farming alone does not supply enough nutrients, and organic fertilizers need to be supplemented by a basal dressing of chemical fertilizer. Field tests which compare the effect of chemical and organic fertilizers tend to find that in the short term, plants respond to the nutrients each type of fertilizer contains. If these are the same, then so generally are the yields.
However, over a longer period of time, applications of organic materials such as livestock manure and crop residues have been found to bring about a gradual improvement in soil productivity and crop performance. A recent study carried out on five crops in Japan showed that applications of organic matter enhance root growth and nutrient uptake, resulting in higher yields.
Another benefit from the increased use of organic materials is that it can help solve pollution problems caused by agro-industrial wastes and intensive livestock farming. However, the soil must not be seen as a dumping ground for organic wastes. If too much nitrogen fertilizer is applied, whether in the form of organic matter or chemical fertilizer, some of the excess nitrogen is converted to nitrates, which are harmful to human health. Improper use of organic fertilizers can cause nitrates to accumulate in groundwater, and also in crops if they are taken up by the plant roots.
The value of organic materials as a source of plant nutrients is greatly enhanced by composting. Composted materials are also more stable and pleasant to handle. In Thailand, a major exporter of rice and cassava, the loss of soil nutrients represented by the export of bulk commodities is now being repaired by a major program to encourage farmers to use more compost. A national extension program is being carried out to teach farmers efficient composting methods.
Under this program, compost production has risen from 57 thousand mt in 1981 to its current level of well over 800 thousand mt/year. In the method generally recommended to Thai farmers, plant residues are layered alternately with livestock manure at a rate of 10:1 (by weight) to make a pile around 1.5 meters high. Urea is often added to the compost pile, and sometimes rock phosphate. A microbial inoculant is often added to hasten decomposition. An inoculant is produced by the government and distributed through the national extension services.
If organic farming is to be practiced by farmers, it must be profitable. Organic food needs a special marketing channel, since it usually has a poorer appearance than food grown using chemicals but is otherwise impossible to identify. In Japan, many organic farmers sell directly to consumers' associations.
Few studies have yet been done on the effect of organic materials on soil microorganisms. One study carried out in Japan found that the application of livestock manure and other organic materials resulted in a more diverse root fungal flora. Solid organic materials produced more diversification than liquid ones.
In contrast, continuous monocropping reduced diversity, which may be partly why soils where the same crops are grown continuously are conducive to the spread of soil-borne diseases. Composting diseased stems of Adzuki bean infected with brown rot with straw and other waste products eliminated most of the pathogenic organisms.
From using organic materials to promote a more favorable soil microbiological environment, it is a short step to isolating the active microorganisms and applying them as an inoculant. Microbial inoculants used in agriculture are of three main types. Some are applied to the soil, usually as biological agents for the control of soil-borne diseases, and others are applied to crops (Rhizobium etc.). Sometimes a microbial inoculant is applied to compost piles, to improve the compost and/or speed up the breakdown of organic materials. In the Philippines, for example, a decomposer fungus, Trichoderma reesei, is combined with the nitrogen fixing bacterium Azotobacter to make an inoculant for composted materials. The compost is produced within a shorter time, and has a higher nitrogen count.
Inoculation of crops with beneficial bacteria and other microorganisms is a very active field of research. Several papers presented at the seminar reported on recent work in which soybean and other legumes were inoculated with Rhizobium, a bacterium which occurs naturally on the roots of legumes and forms nodules which supplies the plant with some of its nitrogen. The soil in fields where soybean etc. have been grown for many years contain natural populations of Rhizobium. However, it has been found that inoculation of the seed with improved strains increases the size and nitrogen fixing capacity of the nodules.
In Indonesia, the commercial production and distribution of "Legin", a multi-strain preparation of Rhizobium, began in 1979. This product was later distributed free of charge by the government as part of the soybean intensification programs. There are now about 600,000 ha of soybean which have been inoculated with Legin being grown in Indonesia each year. There has been much subsequent research to isolate even more effective Rhizobium strains. Selected strains of Bradyrhizobium japonicum have been successfully used in Korea for the production of soybean, peanut and alfalfa. Work is now continuing to find the best matches between the Rhizobium strain and the particular host plant. In Malaysia, sesbania inoculated with Azorhizobium is grown as a green manure crop after rice. Nodules form on the stem as well as the roots, which means that the inoculated sesbania can be grown in acid soils and other adverse soil conditions where root nodulation is inhibited. Another nitrogen fixing bacterium, Azospirillum, has recently been used in Malaysia to inoculate oil palm and sweet potato. Azospirillum is usually associated with the roots of grasses such as corn and sugarcane. Effective strains have been isolated and mass produced for commercial sale for use on rice in the Philippines. It gives increased rice yields if applied with inorganic fertilizer, though not if it is applied on its own.
Mycorrhiza, the symbiotic fungi species which grow on and near plant roots, have been used for forestry in Indonesia for some years, and in Malaysia mycorrhiza inoculants have successfully been used for commercial crops for more than a decade. Recent research in Indonesia indicates that the use of inoculants containing mycorrhiza are also effective in increasing the yield of food crops, including rice. In Taiwan, musk melon are inoculated with VA mycorrhiza in order to improve the quality as well as the quantity of the yield. Research in Thailand has found that effective species of VA mycorrhiza can replace phosphate fertilizers in soils with a low with a low available phosphorus content. Corn or sorghum are used as the host plants.
Composting technology is well established, and the benefits of applying compost are widely known. In areas where farmers seldom make use of compost in their actual farm practices, the constraints are more likely to be socio-economic than technical. Government programs like that in Thailand to promote compost production and use are often very effective.
With regard to microbial inoculants, while their potential is enormous there was some difference of opinion among seminar participants concerning the effectiveness of microbial inoculants currently available. Some felt that the performance of these products is often disappointing, and nearly always much less than the claims made by the manufacturer. Others felt that some products give good results, although others do not meet the exaggerated claims made for them. In most Asian countries, farmers tend to be more enthusiastic about microbial inoculants than the scientific community. Farmers spend large sums of money on them, which many scientists feel is wasted. It was pointed out that microbial products contain living organisms, and their performance therefore largely depends on whether they are used in a favorable environment. Because of this, results are bound to be rather inconsistent. It may even be that farmers are more skilled in selecting or creating a good environment in which these products are effective than the research scientists who test the products on research stations.
At the seminar, several suggestions were made on how to improve the effectiveness of microbial products: Mixed cultures containing several lines or species are likely to do better than pure cultures, although even these tend to be soon overwhelmed by the native soil microflora so that the effect is only short-term. Several participants emphasized the need to know more about the mode of action of beneficial species, if populations in the soil are to be manipulated successfully so as to minimize soil-borne diseases and maximize plant health. It was also recommended that the mode of action of microbial inoculants be determined, and the dispersal and survival of the inoculate in the soil be monitored. Quality control was suggested as another important point. This is always a difficulty with biological products, because the mass production of living organisms tends to select those best suited to mass production, rather than those which are most effective in the field.
Location: Suweon, Korea
Date: June 13-18 1994
No. Participating Countries: 8 (Indonesia, Japan, Korea, Malaysia, Philippines,Republic of China, Thailand, United States)
No. Papers: 14
No. Participants: 26 plus observers
Co-sponsors: Rural Development Adminstration (RDA), Korea
1. Keynote speech: Use of microbial inoculants and organic fertilizers in agricultural production
- James F. Parr, S.B. Hornick and D.D. Kaufman
2. Effect of application of compost and manure on crop growth, nitrogen mineralization and nitrogen uptake under rice-corn rotation
- Tzo-Chuan Juang
3. Roles of organic fertilizers in promoting soil microbiological fertility
- Tsuneo Nitta
4. Biofertilizers and their application, and processing of compost in Indonesia
- Iswandi Anas
5. Selection and use of effective strains of rhizobium in Korea
- Ui-Gum Kang and Ho-Sung Ha
6. Selection and application of biofertilizers in Taiwan agriculture
- Chiu-Chung Young
7. Microbial materials and soil amendments in Japan- Naoto Owa
8. The research and utilization of soil of biofertilizer in Thailand
- Bunharn Tangcham
9. The use of organic wastes for the organic fertilizers in Korea
- Kwang-Young Jung
10. Application of microbial inoculants for crop production
- Zulkifi H. Shamsuddin
11. Composting and agricultural production in the Taiwan area.
- Shang-Shung Yang
12. General review of processing of compost in Thailand
- Chawalit Hongprayoon
13. Use of bio-organic fertilizers in agricultural production in the Philippines
- Modesto R. Recel
14. Status of microbial fertilizers in the Philippines
- Reynaldo E. Dela Cruz
15. Some aspects of use of microbial and organic fertilizers in agricultural production in Korea
- Chong-Woon Hong and Kwang Nam Hwang
Figure 1 Roots of Soybean Plant with Nodules Formed by Rhyzobium
Figure 2 Primordium of Nodule Formed by Azorhizobium on Sesbania Stem. (Photo by Courtesy of Zulkifli H. Shamsuddin)