New Developments in Composting
International workshop on compost production and use
Compost Quality
Quality control is one of the most important problems in compost production, and one of the most difficult to solve. Commercial compost plants are often processing a variety of raw materials from different sources. Common materials are livestock manure and the by-products from food processing. Food wastes often have a high level of salt, while livestock manure may be contaminated by heavy metals. Agro-industrial wastes sometimes contain toxic enzymes or organic acids which injure crops.
It is important that contaminated materials are not included in commercial compost, to avoid crop damage. This is especially vital if the crop is to be used as human food or livestock feed. Otherwise, toxic materials may enter the food chain.
Compost Application
Compost is a soil amendment as well as a fertilizer. Applying compost to strongly acid clay soils in Taiwan improved the availability and mineralization of soil nitrogen. The combined use of organic and chemical fertilizer gave better results than if either type of fertilizer was used alone. In the Philippines, a national program to improve rice fertilization is combining both compost and mineral fertilizers as a balanced nutrient source. This program gives most farmers a marked increase in rice yields.
Large-Scale Composting of Plantation Wastes
The oil palm industry in Malaysia 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. These are now being used as a raw material for composting. They are usually shredded before they are composted, and 20-30% chicken manure is added. Since the EFB are very porous, the mixture is generally watered every day to keep the compost moist. A fungal inoculant has been found to accelerate the composting process. This produces mature compost in about six weeks.
In similar programs, sugarcane bagasse is being composted with microbial inoculants in Vietnam. Urea and other nutrients are added to the mature compost, which is sold as biofertilizer. In Korea, the sludge left after processing potato starch is being mixed with chicken manure and composted.
One advantage of using oilpalm wastes for compost production is that oilpalm are harvested throughout the year. Sugarcane and potato, on the other hand, have a seasonal harvest, as do most other agricultural crops. Composting plants need a steady supply of raw materials if they are to operate efficiently and make best use of their machinery and labor force.
Compost Pellets
Intensive livestock production in Asia produces huge quantities of animal manure each year: around 97 million tons in Japan, for example, and 35 million tons in Korea.
Livestock producers may not have access to enough cropland for recycling all the composted manure they produce. However, even after drying, compost is bulky and expensive to transport. A new formulation converts livestock compost into pellets.
Pelleting reduces the volume of compost by compression. There are other advantages. Compost pellets can be spread onto fields by machine. Applied to upland soils, pellets retain their shape for a long time and decompose slowly, acting almost as a slow-release fertilizer.
However, they are more expensive than ordinary compost. Farmers can afford them only if crop prices are high.
Conclusion
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.
In the long term, the quality of the product must outweigh the advantages and profits of waste disposal. Regulations of toxic elements in compost for long-term application should be established. Monitoring soil and crop quality after compost applications is also important.
A common trend in Asian countries is that fewer farmers are composting on the farm. Instead, wastes from a number of farms are being collected and processed in a local compost plant. Most Asian farms are too small to maintain an efficient mechanized composting system. Composting by manual labor is exhausting and time-consuming. It is hardly surprising that most Asian farmers today prefer to buy compost rather than to make it.
Commmercial composting plants are likely to operate most efficiently if they have acess to a large volume of a standardized product, such as sugarcane bagasse. Another advantage is if raw materials are being produced throughout the year. This helps compost plants to maintain a steady output and minimize their production costs.
Index of Images
Figure 1 On-Farm Composting, Thailand: Rice Straw
Figure 2 On-Farm Composting, Taiwan: Livestock Wastes
Figure 3 Extruder to Make Compost into Pellets
Figure 4 Freshly Cut Oilpalm Fruit
