This workshop was the latest in a series of FFTC meetings on compost production, quality control and application. It covered two main aspects: recent developments in the technology of composting, and their application in Asian agriculture.
Asian countries produce large quantities of food processing wastes every year. In Japan, the food processing industry generates around 3 million tons, 38% of which is recycled. About half of this total is made up of sludge, and a quarter is vegetable residues, while the remaining residues are varied in terms of both their raw materials and nutrient content.
Sludge is usually treated on-site to reduce the water content, and thus the cost of transport. After drying, sludge has an average nitrogen (N) content of around 7%. It is recommended that wastes with a high level of N, such as those from meat processing, be mixed with those with a low level of N to produce a compost which is suitable for general use.
Government policies in Japan emphasize the recycling of agro-industrial wastes, and a reduction in the generation of new wastes.
Livestock manure is another organic waste which is produced in huge quantities in Asia. Livestock production in Korea produces about 35 million tons of manure each year. Japan produces 97 millions tons of livestock manure annually, while Taiwan produces 6.6 million tons (on a wet basis). Most livestock are raised in feedlots. Manure disposal from livestock raising is a major problem, both at a farm level and nationally.
Studies have shown that about 70-80% of the nitrogen fed to livestock is excreted in the manure, and around 80% of the phosphate. An examination of small-scale composting plants found that 10-25% of the nitrogen content of the original livestock manure is lost in the form of ammonia gas (NH3).
Livestock production tends to be found in particular areas such as uplands. These may lie some distance from arable areas where compost is needed. This makes recycling difficult, because livestock manure is a bulky product which is expensive to transport, even when it is composted and dried. A new formulation converts livestock compost into pellets. This reduces the volume by compression. The pellets can be spread onto fields by machine. Applied to upland soils, pellets decompose slowly, behaving almost like a slow-release fertilizer. However, farmers can afford them only if crop prices are high, since the pellets are more expensive than ordinary compost.
Malaysia is the world's largest oil palm producer, with more than three million hectares of oil palm plantation. The oil palm industry generates around 90 million tons each year of renewable biomass. About 8 million tons of this is the empty fruit bunches (EFB) left after the oil is extracted. In the past, these were often burnt as fuel by oil palm extraction mills. However, new environmental regulations now forbid this practice because of air pollution. One paper presentation discussed various methods of composting EFB in open and closed systems, and mixed with various other materials.
An open compost pile protected from rainfall, using a mixture of EFB and 20-30% chicken manure, was found to be the best system. A fungal inoculant was found to accelerate the composting process, making it possible to produce mature compost in about six weeks. Fresh compost was inoculated, not by isolating the spores, but by recycling around 10% of the mature compost into fresh composting mixture.
Most EFB composting plants are fairly small, located near or in the oilpalm plantation to reduce transport costs. A major problem is the cost of the equipment needed for mixing and shredding the EFB compost.
Sugarcane wastes are another common crop residue in Asia. One hundred mt of sugarcane yields only 10-12 mt of sugar, the rest is made up of by-products and wastes (23-28 mt of bagasse, 3-4 mt of The demand for compost is also intermittent. Farmers usually apply compost only once or a few times a year, just before planting and/or after harvest.
This irregularity in both the supply of raw materials and demand for the product means higher costs. The high price of commercial compost - around US$2.00 for a 20 kg bag in Korea - limits its use, and encourages farmers to seek out cheaper low-grade composts. In terms of the nitrogen content, compost is 20 times more expensive than chemical fertilizer in Korea.
Livestock manure has the advantage that there is a regular supply throughout the year. However, it is often contaminated by heavy metals. Livestock and poultry producers generally include mineral supplements in the feed. Although the amounts given are very small, minerals such as copper and zinc tend to accumulate in compost and contaminate the food chain.
Furthermore, the areas where livestock are produced may lie some distance from arable areas where the compost is applied. Livestock producers may not have access to enough cropland for recycling all the composted manure they produce. Livestock manure is a bulky product which is expensive to transport, even when it is composted and dried. Pelleting may help solve this problem, but the product is expensive, and can only be used in countries where farm incomes and crop prices are fairly high.
Composting has two main functions: to provide farmers with organic fertilizer, and to recycle organic wastes. The two aims are not necessarily in conflict. However, if the recycling function becomes too important, there is a danger that sub-standard raw materials may be used, simply as a way of disposing of them.
In this case, compost quality may be poor. It may also be variable, so that farmers do not really know what plant nutrients they are applying. Compost may even contain toxic substances, and inhibit crop growth rather than promote it.
Composting is only useful if the product can be used, which means it must be reliable in terms of maturity, quality and nutrient content. In other words, in the long term, the quality of the product must outweigh the advantages and profits of waste disposal. Regulations of toxic elements in composts for long-term application should be established. Monitoring soil and crop quality after compost applications is also important.
Held at National Chung-Hsing University, Taiwan ROC, May 21-26
No. of participating countries: 8 (Indonesia, Japan, Korea, Malaysia, Philippines, Taiwan ROC, Thailand, Vietnam)
No. of papers: 14
No. of participants: 14 plus 80 observers
Co-sponsor: National Chung Hsing University
Figure 1 Farm Compost Heap Covered in Rice Straw
Figure 2 Modern Compost Plant, Korea