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Microbial Inoculants in Asian Agriculture

Abstract

The goal in developing sustainable agriculture is to find models which strike an acceptable balance between production benefits and ecological conservation by the reduced use of chemicals, pesticides or other harmful materials. The use of biological materials such as microbial fertilizers and compost, as well as improved crop varieties and animal breeds, will be of basic importance.

Organic and Microbial Fertilizers

The value of organic fertilizers, not only to provide plant nutrients but to help control soil-borne diseases and maintain adequate soil structure, is now being widely recognized. So is the role of microbial fertilizers, as a low-cost and non-toxic method of controlling soil-borne diseases, improving nutrient uptake by plants, and increasing the supply of soil nutrients.

There is also an urgent need to reduce pollution from agricultural wastes, especially those from intensive livestock production and agro-industrial processing. Better composting methods will change these from a problem into an asset. The small farms and intensive agriculture typical of Asia require very efficient composting methods, so that a large mass of materials can be processed into compost within a small area and within a short space of time, with a minimum of noxious odors. Microbial inoculants are a very promising new development in improved composting methods.

This training course introduced young scientists and extension specialists to some of the most recent technical information concerning microbial inoculates and composting. It is a follow-up to an international seminar on the use of microbial and organic fertilizers in agricultural production which was held in Korea in 1994, and is one of a series of training courses and workshops on microbial fertilizers and composting. The first of these training workshops was held in Suweon, Korea in 1995 in cooperation National Agricultural Science and Technology Institute, Rural Development Administration. This second training course took place at the Taiwan Agricultural Research Institute (TARI), and further courses on this topic are planned for the future. The course at TARI introduced the technology developed in Taiwan for microbial products, and discussed its use both in the laboratory and in the field; techniques of analysis and methods of field sampling; and the problems of quality control and evaluating the effectiveness of such products. Another important topic covered by the course was composting, including problems such as bad odors during fermentation; effectiveness and price of organic fertilizers compared to chemical ones; criteria to evaluate compost quality; and the problem of soil contamination from heavy metals. 

Am Fungi

Arbuscular mycorrhizal fungi (AMF) are an important group of soil-borne microorganisms that contribute substantially to the productivity of natural or man-made ecosystems. These fungi form symbiotic association with most terrestrial plant families. They have an extensive network of external hyphae which function as plant rootlets and increase P uptake. They were formerly known as "vesicular-arbuscular myccorrhiza" or VAM. However, since some of the mycorrhizal fungi such as Gigaspora spp. do not produce vesicles in the roots, they are now generally referred to as AM fungi, or AMF.

Because AM products are expensive, they are mainly used for the production of high-value crops such as fruit and vegetables. The most promising areas for practical use of AM in horticulture is for nursery seedlings grown in plugs, and for plantlets grown by micro-propagation plantlets. Inoculation with AM fungi has been found to increase the survival rate of micropropagated plantlets. It should be done when micro-propagated plantlets are being transplanted out of test tubes. For seedlings grown in plugs, inoculation when the seed is sown gives faster growth, greater resistance to disease and higher yields.

There are also potential applications for plants grown in fumigated soil, in soiless media and in arid or infertile areas. Japanese scientists are testing AM fungi to help establish vegetation cover on barren land such as road cuttings, recent falls of volcanic ash, and construction sites. Good results are being achieved through the use of plastic webbing, used to cover bare soil. It contains plant seeds and fertilizer, together with a growing medium of organic materials, zeolite etc. Plant growth is more rapid if the sheet is inoculated with AM fungi.

In Taiwan, AM fungi are being used to inoculate muskmelon. The seedlings are inoculated before they are transplanted into the field. Trials of muskmelon grown in plastic nethouses and plastic tunnels found that the plants treated with mycorrhiza had a faster growth rate and bloomed seven days earlier than the non-treated ones. Both the quantity and quality of fruits were also improved. Because inoculated muskmelon have a very healthy and extensive root system, it is possible to grow a second ratoon crop of fruit.

About 51% of upland fields and grasslands in Japan are on volcanic ash soil with bound phosphorus and strong acidity. Phosphate availability is therefore one of the strongest limiting factors in upland farming. Large amounts of phosphate have been applied, particularly to fruit and vegetables. While these have led to a marked increase in yield, many vegetable fields have accumulated phosphate to levels which inhibit plant growth. On the other hand, many grasslands are deficient because not enough phosphate has been applied. In both situations, there is great interest in using AM fungi for soil amelioration. The action of the AM fungi has been found to be stimulated by the use of charcoal, possibly because the large pores in the charcoal offer a new micro habitat to the fungi, enabling them to extend their mycelia and take up nutrients far out from the plant roots.

Since AM fungi are living organisms, it is important that they be used in an environment which is conducive to their growth and reproduction. Furthermore, various strains of the same species may differ greatly in their effectiveness. It was emphasized at the meeting that it is very important to select species and strains of endo- and ecto-mycorrhizal fungi best suited to the particular soil and host crop.

For some time, the practical use of AM fungi was limited by the low infectivity of AM in soil with a high phosphate content. This problem can now be partially solved by growing inoculated seedlings in plugs then transplanting them into field soil. Even if phosphate levels in the field are high, the beneficial effects of the AM will still be significant.

Biological Nitrogen Fixation and P-Solubilizing Bacteria

Nitrogen input to the soil from both biological and non-biological sources is essential to sustain agricultural productivity. There is an increasing interest in the use of Rhizobium to inoculate soybean and other legumes. This is a bacterium which occurs naturally on legume roots, and forms nodules which provide some of the plant's nitrogen needs. Inoculating seeds with improved strains increases the size of the nodules and their nitrogen fixing capacity. Work is now in progress to find the best matches between particular Rhizobium strains and the host plants.

P-solubilizing bacteria have been reported to increase the P uptake and yield of many crops, and to change insoluble P in soils into soluble forms by producing organic acids.

Composting

Compost is sometimes used by farmers as a replacement for chemical fertilizer, and sometimes as a supplement. It is now widely accepted that long-term use of chemical fertilizer alone can lead to a gradual decline in soil productivity. Composted organic materials applied to the soil can give pronounced benefits in terms of better plant health, soil fertility and crop yields. Some farmers are using organic fertilizer alone, in an organic farming system. Others are continuing to use chemical fertilizer as the main source of plant nutrients, but are combining it with applications of organic fertilizer. Which farmers choose partly depends on individual preference, but also partly on whether there is a good marketing system for organic produce.

Another benefit of composting is that it is a means of recycling waste materials. Participants at the training course studied recent research to accelerate the composting process, and reduce unpleasant odors during this period. Among the raw materials studied as composting materials were livestock manure and sugarcane bagasse.

One of the most common materials used in compost is rice straw. Even when it is chopped, rice straw is slow to decompose, although it decomposes more quickly than wheat straw. A number of microbial products are available to hasten the decomposition of straw, and improve the nutrient value of the final product.

Malodorous gases emitted during the treatment of livestock manure or agro-industrial waste can cause serious air pollution, as well as being a source of annoyance to those living nearby. There are various ways of controlling such odors, including physical methods (adsorption-activated carbon and water-washing); chemical methods (high temperature incineration or chemical agents); and biological methods (biofiltration and bioscrubbing). Most techniques currently in use are based on physical and/or chemical principles. However, a more recent technology - the biological deodorization processes - seems to be very promising. Odor control is very effective, while operation and maintenance costs are low, and no fuel or chemicals are required.

Although organic and chemical fertilizers are often used in combination and applied to the same field, they are usually produced and applied separately. However, there is a growing interest in organic compound fertilizers, which are composted materials supplemented with chemical fertilizers to give an optimum nutrient balance for the needs of particular crops.

Conclusion

The microbial products and organic fertilizers now being sold to farmers share a common problem: that of quality control. Compost is made from a range of organic materials with various nutrient compositions. It is very difficult to ensure that the products is a standard one. For this reason, most commercial organic fertilizers are not covered by the type of national standards which govern the quality of chemical fertilizers. A number of private composting plants are producing many kinds of organic fertilizer. Their products are often of poor quality, and also contain unknown amounts of chemical fertilizers, in proportions unsuited to crop needs. There is an urgent need to define standards for organic fertilizers.

With regard to microbial products, most of them are not microbiologically defined (i.e. the microorganisms they contain are not identified). A few do define the microbial species, but almost none give quantitative data. Microbial products tend to be advertised in very glowing terms, as if they can solve any problem the farmer is likely to encounter. None of these claims have been proved, and many of them are probably untrue.

Both organic fertilizers and microbial products tend to be expensive. The effectiveness of compost is largely related to the nutrient it contains, so it is important that the price of compost on a nutrient basis should not be too much higher than the cost of chemical fertilizer. Some price differential can be accepted, because of the high labor costs of composting, and because of the effect of compost on the soil's chemical and physical properties. However, in some cases the price of commercial compost is far too high, and the prices charged are not justified by the farmer's returns. Along with standards, there is a great need for simple and accurate ways to measure the effectiveness of commercial organic fertilizers.

Finally, there is a considerable difference in the effectiveness of different strains of Rhizobium or AM fungi. Furthermore, a strain which is effective for one crop and variety may be completely useless when used with another. More research needed to classify and define strains of AM fungi and other beneficial organisms, so a good match can be made between the particular strain(s) used in a microbial product, and the host plants it is expected to benefit.

FFTC International Training

Course Microbioal Fertilizers and Composting

Location:

Taichung, Taiwan ROC
Date: October 15 - 22, 1996
No. Participating Countries: 7 (Indonesia, Japan, Korea, Malaysia, Philippines, Taiwan ROC, and Vietnam)
Lectures delivered: 12 (plus hands-on training)
No. of Participants: 40 plus observers
Co-Sponsors: Council of Agriculture, Executive Yuan, ROC
Taiwan Agricultural Research Institute

List of Papers


1. Classification and Inoculum Production of VA Mycorrhiza- Chi-Guang Wu
2. Arbuscular Mycorrhiza (AM) in Horticulture
- Doris C. N. Chang
3. Application of VA Mycorrhizal Fungi on Production of Melons
- Y. H. Cheng
4. Microbial Fertilizers in Japan
- Michinori Nishio
5. Biological Nitrogen Fixation and Phosphorus-Solubilizing Bacteria
- Chiu-Chung Young
6. Bioreactor of Compost
- Tao-Nan Chien
7. Recycling and Utilization of Bagasse
- Chi-Min Huang
8. Composting of Animal Waste
- Shao-Yi Sheen
9. Examples of Cattle Manure Composting in Japan
- Toshihiko Ibuki
10. The Influence of Various Bio-filters on the Deodorizing Efficiency of Ammonia and Hydrogen Sulfide
- Ming-Muh Kau and Chun-Cheng Tang
11. The Manufacturing Processes and Application of Organic Compound Fertilizers
- Tso-Chuan Juang
12. Quality of Compost
- Shang-Shyng Yang

Laboratory Sessions:

  • 1. Practice in Biological Nitrogen-Fixing and P-Solubilizing Bacteria
  • a. Collecting Nodules and Isolating Bacteria
  • b. Authenticating the Isolates as Rhizobia
  • c. Isolation of Phosphate-Solubilizing Bacteria
  • 2. Practice with VA Mycorrhiza Fungi
  • a. Isolation of VA Mycorrhiza Fungi
  • b. Morphology of VA Mycorrhizae
  • c. Making Semi-permanent Slides of VA Mycorrhizal Fungi
  • d. Propagation of VA Mycorrhizal Fungi
  • 3. Preparation and Characterization of Compost
  • a. Materials Suitable for Composting
  • b. Conditions for Composting
  • c. Methods of Composting
  • d. Evaluation of Changes in Compost

Index of Images

Figure 1 Plastic Webbing Being Laid on Steep Bare Slope in Japan. the Webbing Contains Am Fungi, Grass Seeds, Fertilizer and Organic Materials. It Protects the Soil of New Road Cuttings Etc. While Vegetation Is Becoming Established.

Figure 1 Plastic Webbing Being Laid on Steep Bare Slope in Japan. the Webbing Contains Am Fungi, Grass Seeds, Fertilizer and Organic Materials. It Protects the Soil of New Road Cuttings Etc. While Vegetation Is Becoming Established.

Figure 2 Same Slope a Few Months Later, with Established Grass Cover

Figure 2 Same Slope a Few Months Later, with Established Grass Cover

Figure 3 Inner Surface of Plastic Webbing

Figure 3 Inner Surface of Plastic Webbing