We still know very little about the interactions between different species of soil microorganisms, or between microorganisms and crop species. However, we are becoming increasingly aware that biologically active soil helps control soil-borne diseases and promotes plant vigor.
Although farmers in Asia have been making organic materials into compost for centuries, science can make composting more efficient by speeding up the process of composting and improving the nutrient quality of the end product. Modern agriculture in Asia tends to be highly intensive, with three or even four crops a year. Farms are small, which means that space is precious and a rapid turnover of composted materials is desirable. in the air or soil into a form which plants can use, while other species can assist in the control of soil-borne diseases.
The improved use of biological resources and the understanding of interspecific relationships will be a major component of the sustainable agriculture of the future. While agricultural research and extension have done much to increase our understanding of crop and livestock species, we are only beginning to learn about the very tiny species which inhabit soil and compost, and which are responsible for many of the vital mechanisms of plant growth.
The more nutrients that are available to plants, the higher the yield. Mineral nutrients are known to circulate through a chain of plants, soil and animals, but it is soil microorganisms that change these nutrients into a form available to plants. In sustainable agriculture, it is important to make full use of all microorganisms in order to promote the circulation of plant nutrients and reduce the use of chemical fertilizers as much as possible.
Biological nitrogen fixation is a biological process catalyzed by the enzyme nitrogenase. This process converts atmospheric nitrogen (N
2), which is not in itself available to plants, into the form NH
4 which plants can use. The cost of using biological nitrogen fixation in agriculture is low compared to chemical fertilizers, and saves energy. Biological nitrogen fixation is carried out by several organisms, mainly microorganisms, in natural ecosystems.
Effective rhizobium strains should be taken from rhizobium present in nodules rather than those present in the soil, since the soil is not generally a selective medium.
The root site is known to be a unique microsite for the association of symbiotic and non-symbiotic organisms. Infecting crop roots with vesicular-arbuscular mycorrhizal (VAM) fungi can improve their uptake of phosphorus and other nutrients, resulting in an increase in yield. Preparations containing VAM fungi are already being extended to farmers in Taiwan for the improved production of muskmelon and other high-value crops.
Composting provides an appropriate porosity, density and moisture content so that easily degraded components of the substrate are broken down, while at the same time pathogens and weed seeds are killed and the organic materials become stabilized. For rapid decomposition by microbes, the substrate should have a C/N ratio of 30-40, a pH of 6-8, and a moisture content of 60-70%. Materials commonly used for compost in Asia include livestock manure, various crop residues, and municipal refuse. Controlled conditions are important in composting.
An important problem is how to estimate the degree of compost maturity. Farmers making compost on their own farms need a simple, reliable method. The germination test is the standard method used to evaluate compost quality, but this may not be easy or convenient for farmers to use. A new infrared technique is being developed, byut this may be too expensive and complicated. Experienced farmers can evaluate compost by its smell, and also by its texture when handled - if it feels sticky, the moisture content is probably too high.
Another problem is the permissible levels in compost of heavy metals. These tend to persist in the food chain and are often present at high levels in organic materials, particularly livestock manure and municipal wastes. While some countries such as USA have fixed maximum limits, it was recommended at this workshop that the concentration of heavy metals in compost should not be higher than the level found in background soil.
The quality of compost made by small-scale producers tends to be highly variable. Differences in the N, P and K content reflect differences in the quality of the raw materials which are beyond the control of the producer, but the wide variation in pH and ammonium N content deserve more attention. Ideally, compost should have a pH of around 7, but in practice the pH is often higher than this, sometimes resulting in symptoms of iron deficiency. A high ammonium content is probably because insufficient time has been given for the compost to mature. It was recommended at the training workshop that extension specialists and scientists working with farmers should find out which factors are responsible for poor quality in compost, and find the means to correct them.
No. Participating Countries: 7 (Indonesia, Japan, Korea, Malaysia, Philippines, Taiwan ROC, Thailand)
No. Papers: 6 lectures and 3 practical sessions
No. Participants: 6 lecturers and 14 trainees, plus observers
Co-sponsor: Rural Development Adminstration (RDA), Korea
1. Biological nitrogen fixation (plus practical session)
2. Isolation and selection of va-mycorrhiza and p-solubilizing bacteria from soils (plus practical session)
3. Preparation and characterization of compost (plus practical session)
Dr. Shang-Shyng Yang
4. Practical aspects of animal waste composting in Japan (plus practical session)
5. Problems involved in producing compost from organic wastes of different sources
Chong Woon Hong
6. Problems involved in the use of compost
Chong Woon Hong
Participants also recieved hands-on training in various laboratory skills, including isolation of effective rhyzobium strains, inoculation of legume seeds with rhyzobium in order to promote nitrogen fixation by the growing crop, and the isolation and selection of VAM fungi and P-solubilizing bacteria
Figure 1 Training Course on Microbial Fertilizers.1
Figure 2 Training Course on Microbial Fertilizers. 2