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Quality Control for Commercial Compost in Korea
Myung Ho Um and Youn Lee
National Institute of Agricultural Science and Technology (NIAST),
Rural Development Administration (RDA),
Suwon 441-707, Korea, 2001-10-01

Abstract

Many countries are now trying to protect the agricultural environment by restricting activities which may harm it. The Korean government is attempting to reduce the environmental pollution from excessive chemical fertilizers, pesticides and livestock manure. Since the early 1990s, the government has accepted a policy of sustainable agriculture. Under this policy, the use of chemical fertilizer has gradually been reduced, but consumption is still too high. To reduce the levels of chemical fertilizer, the government is trying to use livestock manure more efficiently as a nutrient source. However, Korea is very cautious about using waste materials from industry and municipal areas for composting. Before being composted, such materials must be inspected. The government is focusing on a full-time inspection system for commercial fertilizers, and on education for the people engaged in fertilizer production. Making good compost from organic wastes, and appropriate use of compost for crop production, are important in terms of both environmental protection and food safety. The production of organic wastes by different industries is monitored, and their value as a raw material for composting should be carefully examined. The trust of consumers in agricultural products comes from the continuous effort to maintain quality. Standards for grading maturity, and recommended compost applications for crop production, are expected in the near future.

Introduction

From the 1960s, agricultural policy in Korea supported high applications of chemical fertilizers to maximize agricultural output. As a result, the soil organic matter content decreased, becoming a barrier to increased agricultural productivity. Also, massive inputs of chemical fertilizer caused salt accumulation and an imbalance of nutrients in soils ( Table 1(1296)). The deterioration in soil quality became an important issue.

Since the government adopted a policy of sustainable agriculture, the use of chemical fertilizer in agriculture has been gradually decreasing. The government has tried to reduce fertilizer inputs further by introducing less concentrated formulations, and adjusting fertilizer recommendations for crops. However, the results have fallen short of the government's hopes. Recently, both the production of various organic wastes (especially livestock manure) and their use in agriculture has increased ( Table 2(1058)). The government is promoting the recycling of organic wastes in the field.

Composting organic wastes on farms is difficult because of a shortage of labor and the intermittent supply of raw materials. Industrialized composting is popular in Korea, with livestock manure as the main raw material. Two important rules in using compost on fields are that the amount of applied compost should not exceed the nutritional demand of the crop, and its use must ensure that agricultural products are safe. This report refers to the production of compost and its evaluation. Also, the process of approving organic wastes for use as a composting material, and quality control of commercial composts, are discussed.

Characteristics of Raw Materials for Composting

The selection of composting materials is important, since it has a direct influence on compost quality. There is little possibility of including harmful materials in composting rice straw, but the increasing use of livestock manure, and industrial and municipal wastes, is a concern. Needless to say, the purpose of compost is to improve soil quality and to produce high-quality crops. It is not a means of disposing of organic wastes. Therefore, the selection of good raw materials for composting is crucial in quality control.

Raw Materials for Composting

Agricultural by-products

Agricultural by-products in general have a low nutrient content ( Table 3(1185)). Rice straw and rice hull are produced in large quantities in rural areas. They have a relatively high potassium content (1.84%), while the C/N ratio is high (1:50). They break down very slowly, and rice hull sometimes needs prior processing (e.g. puffing). Such materials are mainly used as bulking agents in composting livestock manure, rather than as major composting materials.

Forestry by-products

Sawdust is a major by-product in forestry. It is not a good raw material for composting, because of its high C/N ratio and low nutrient content ( Table 4(1288)). Since it has a low bulk density and can hold moisture, it is often used as a bulking agent for wet materials.

Livestock manure

The number of livestock in Korea has been increasing rapidly with the growth in meat consumption since the 1980s. The production of livestock manure in 1999 was 34.9 million mt. Livestock manure has been used for composting for a very long time, and in the past was considered the main source of organic fertilizer for crop production. Livestock manure varies in its C/N ratio and nutrient content ( Table 5(1261)). It has a higher phosphate and potassium content than most other organic wastes. The heavy metal content is very low, compared to the levels found in industrial and municipal waste. Only pig manure may have a high copper content, coming from the feed materials.

The total nutrient content in the livestock manure produced in Korea each year is considerable ( Table 6(1390)). It could replace most of the 6.1 million mt of chemical fertilizer applied in 1997.

Municipal wastes

The daily production of sewage sludge in Korea is 3,400 mt. It is expected to reach more than 4,000 mt by 2010. Sewage sludge is used as a fertilizer in some countries, including the United States. In Korea, it is used for reclaiming swampland and coastal flats. Sewage sludge has a relatively high nutrient content ( Table 7(1168)). It can be used as an organic fertilizer without composting. However, it cannot be applied to edible crops, because of the high content of heavy metals, and the possibility of harmful microorganisms.

Table 8(1024) shows the nutrient content of human sewage. Human sewage has a high phosphate content. The heavy metal content is lower than in sewage sludge, which often includes industrial wastes. However, the lead content of human sewage may be high, and there are cases of very serious heavy metal contamination.

The amount of food refuse produced each day in Korea in 1998 was 11.8 thousand mt. Since most food wastes come from agricultural products, it seems reasonable to use them as a raw material for composting. However, there is the problem of their high salt content. It is recommended to mix food wastes with livestock manure for composting, or use them in earthworm production ( Table 9(1320), Table 10(1204)).

Industial wastes

The materials in industrial wastes such as sludge vary greatly, and some may be harmful. It is necessary to analyze the chemical content of such wastes before they can be used for composting. Sludge from food processing has a relatively low heavy metal content, but there are cases of 400 mg/kg of lead. Sludge from the food industry needs to be examined for heavy metals. Sludge from the food processing industry which contains no harmful materials is already being used as organic fertilizer.

Sludge from the dairy industry has a higher nitrogen content than other types of industrial sludge. Since it also has a relatively low level of harmful materials, it is often used as organic fertilizer for edible crops. Sludge from the oil industry has a high organic matter content and a low nitrogen content. It contains as high a level of heavy metals as sewage sludge, and there are some reports that it has a damaging effect on plant growth. Sludge from the oil industry is not recommended for crop production.

Sludge from the paper industry has a high C/N ratio. It is sometimes contaminated with lead, which is used in printing. Paper sludge should be dried before being used as a bulking agent when composting livestock manure. Sludge from the alcohol industry has a low C/N ratio, but a high level of nitrogen, potassium and phosphorus. It has been used as an organic fertilizer for some time. However, it is necessary to check the chemicals used for processing and in wastewater treatment. Sludge from beverage production has characteristics similar to those of sludge from alcohol production. It can be recycled in agriculture if it is free of contamination ( Table 11(1290)).

Classification of Raw Materials for Composting

Numerous organic wastes are used for composting. They can be divided into several categories, according to the possibility that they include harmful materials ( Table 12(1167)). Prior examination is required for materials such as sludge from waste-water treatment after processing of food and beverages. Materials that have no nutrient value or which may be contaminated by heavy metals cannot be used for composting. In 1997, the Korean government revised the regulations governing the raw materials used for composting. These distinguished usable materials, unusable ones, and materials which can only be used after examination, ( Table 13(1320), Table 14(1518), Table 15(1470)).

Quality Control for Premium Grade Compost

Management of Composting Materials

Recently, consumers in urban areas have shown an antipathy to chemical fertilizers. They feel that chemical fertilizers contaminate the environment. However, compost made from inappropriate materials can also pollute the environment. Whether compost contains valuable nutrients or harmful materials depends on the raw materials which are composted.

Some people feel that mixing harmful materials with healthy ones can dilute the adverse effect. However, contaminated materials should not be used. There are specific inspection standards for doubtful materials. People who want to use such materials should follow official rules. The standards cover nutrient content as well as the concentration of classified harmful materials. Not only the materials themselves are examined, but also the production lines and waste-water treatments which produce them, ( Table 16(1309)).

In 1999, there were 118 companies in Korea that produced raw materials for composting which required prior inspection. A total of 46 compost facilities were operating which were allowed to use these raw materials for composting. Most of the 118 companies (86%) are processing paper or food, including butchering. However, the use of this category of materials has been decreasing in recent years, since consumers prefer safe agricultural products.

Quality Control of Commercial Compost

In recent years, most composting has been carried out in large commercial plants rather than on farms, because of a shortage of labor in rural areas. Only a few farmers produce compost for themselves. Most farmers buy commercial compost products. Since compost manufacturing companies are looking for cheap raw materials, there is a danger of producing an inferior compost product from substandard materials.

Organic fertilizer and by-product fertilizer

There are two kinds of fertilizers in Korea which contain organic materials. One kind, which includes compost, is by-product fertilizer. The other is organic fertilizer. The differences between the two are shown in Table 17(1238), Table 18(1305), Table 19(1211) and Table 20(1181).

In general, organic fertilizers are more consistent in quality than by-product fertilizer, and there are fewer quality problems. There is more possibility of contamination of by-product fertilizers because the raw materials are so varied. Processing organic wastes into compost can be a profitable business. In 1999, there were 780 composting plants operating in Korea. Of these, two-thirds were making by-product fertilizer.

Of the by-product fertilizers examined in 1999, 18% did not meet the required standard, ( Table 21(1360)). Most violations were the result of too low a nutrient content, and too low a ratio of organic matter to nitrogen. Ten violations were the result of too high a salt content, and 23 cases were high levels of harmful materials ( Table 22(1344)). The fertilizers with a high heavy metal content were made from industrial wastes.

Inspection of imported compost

By law, compost imported into Korea must be inspected to make sure it does not contain any heavy metals or harmful biological materials. Imported compost should be registered with the local government, and inspected by Korea's National Institute of Agricultural Science and Technology (NIAST). Inspection results should be submitted before customs clearance. If the inspection report from the exporting country indicates that the product is safe, inspection can be dispensed with ( Table 18(1305)).

Problems in the Use of Compost

High Price of Commercial Compost

The average price of commercial compost in Korea is about US$2.00 for a 20-kg package. In terms of nitrogen supplied, the price of compost is 20 times higher than that of chemical fertilizer. Although most farmers agree that compost has a beneficial effect, they look for low-grade compost rather than high-quality compost, because it is cheaper. There are some cases of crop damage from low-grade compost made from industrial waste.

Unbalanced Nutrient Content of Compost

Compost made from livestock manure is the main commercial compost in Korea. In recent years, about 100 companies have been supplying sewage sludge as a raw material for compost. The sludge is mixed with livestock manure for composting. Generally, compost in Korea has a high phosphate content.

The average level of nitrogen (N), phosphate (P 2O 5) and potassium (K 2O) in compost collected from 29 companies in 1996 were 1.01%, 2.03% and 0.65%, respectively. If one ton of such a compost is applied, the total amounts of N, P 2O 5 and K 2O will be 10.1, 20.3 and 6.5 kg, respectively. It is impossible to apply recommended fertilizer levels (110-48-68 kg/ha to paddy fields and 157-69-107 kg/ha to upland fields) using only compost of this quality.

Sale of Immature Compost

Composting is carried out in order to minimize the damage from intermediate compounds as organic materials break down. The composting process also adjusts the C/N ratio, and transforms organic materials into a substance which is easy to handle and use. The full composting process takes about six months in a natural environment, and about 80 days in an industrial plant.

There were some cases of immature compost for sale in the market. Biological indicators, or regulations to cover composting temperature and period, are used in some countries to ensure that compost offered for sale is mature. Such regulations on compost maturity are not yet used in Korea.

Salt Accumulation and Environmental Pollution

When livestock manure compost is applied to crops in sufficient quantities to meet the nitrogen requirements, the phosphate input may exceed the recommended level by some 200 to 954%. Heavy applications of compost can damage crops by salt accumulation in soil. Generally, such soils show an excessive accumulation of phosphate, potassium and nitrate. According to one report, 13.6 to 80.7 mg/kg of soluble phosphate may be released from soil that contains 1,600 mg/kg of available phosphate. Although phosphate is easily fixed in soil, it is an important cause of eutrophication of lakes and rivers, even at very low concentrations of 0.02 to 0.07 mg/L.

Quality Control of Compost

Quality control is the process of removing the causes of poor quality of goods. The same principles can be applied to compost as to other manufacturing processes. Manufacturing standards are an indicator of the quality of compost. Since compost-manufacturing standards are based on the supply of organic materials to the soil, there is no regulation of the nutrient content. There are only regulations for heavy metals, to protect the soil from contamination. European countries evaluate allowable heavy metal concentration on a dry weight basis. In Korea, a fresh weight basis is used for analysis. Evaluation by fresh weight is useful for process management, but problems arise if there are variations in the moisture content.

Conclusion

Selection of raw materials for composting

Of the by-product fertilizers tested in Korea in 1996, 42% were below the required quality standard. The percentage of below-standard products had fallen to 11% in 1998, after regulations concerning raw materials had come into force. This shows that compost quality is influenced mainly by the nature of the raw materials. Current regulations cover only minimum standards for quality control. It is necessary to impose further standards to cover aspects such as compost maturity and nutrient value.

If the purpose of compost use is to provide nutrients to crops, livestock manure and plant seed cake are more valuable than rice hull, straw or sawdust. If compost is being used as soil conditioner, on the other hand, materials with a lower level of nutrients can be allowed.

It is important that compost applied in greenhouse is mature. A composting period of more than six months is recommended in this case.

Sometimes, the condensation effect during composting makes contaminants more condensed than in the raw material. It is hard to know whether a raw material contains harmful materials unless it is submitted for chemical analysis. It is highly recommended that the suitability of raw materials for composting should be determined only after thorough discussion with the relevant experts.

Continuous Quality Control for Commercial Compost

Quality control for commercial compost has become more important than ever, since there is a policy of using it to replace chemical fertilizer. The Rural Development Administration (RDA) of Korea is responsible for quality inspection of commercial fertilizers. It is focusing on the education of compost producers. RDA analyzes 700 samples of commercial fertilizers every year, of which 200 samples are collected at production sites. This type of inspection is conducted twice a year. The use of industrial wastes, and sales of immature compost, are to be strictly prohibited, and inspection standards are under development. Practical guidebooks are needed on the application of compost to field crops, and how to use compost without causing environmental pollution.

Grading Policy for Compost

Many people prefer to compost organic wastes rather than use them for land reclamation or incinerate them. In order to protect agricultural fields and to use organic waste rationally, grading of compost is important. Grading can create management problems, but it is very valuable for users. The designation of raw materials, their use in agriculture, current standards of effective or harmful constituents etc. are now being reconsidered.

Restoring Nutrient Balance to Compost

A balanced nutrient content will become a important indicator of compost quality in future. At present, compost made from livestock manure has too high a phosphate content. It needs to be mixed with materials which have a high nitrogen and low phosphate content. Sometimes chemical fertilizer needs to be added to balance the nutrients in compost. Although industrial sludge may be used as a composting material, provided it is inspected and approved in advance, still there is the possibility of contamination from synthetic chemicals such as coagulants. It is necessary to mix such materials with other materials for composting.

Establishment of Safety Standards for Using Compost

Standards for compost use are mainly concerned with composted livestock manure. In general, it is hard to make uniform standards for compost use. Composts differ in their raw materials, while soils and crops also vary. In Korea, a standard application of compost must provide a satisfactory supply of nutrients and act as a soil amendment. Different application protocols are required for each crop.

No application standards for sludge materials have yet been prepared. Although it is cheaper to compost sludge materials than to incinerate them or use them for reclamation, there is the possibility that the final product will contain harmful materials. For the application of sludge materials, it is recommended to use the same application standards as for compost made from poultry or pig manure. Both of these have a relatively low application rate per unit area.

References

  • Dong Kuy Lim. 2000. Utilization of organic wastes for reducing the chemical fertilizers. Working Report, National Institute of Agricultural Science and Technology (NIAST), Korea.
  • Kwang Yong Jung, E.G. Jeong and B.G. Park. 1997. Composting and Utilization of Animal Manure. Rural Development Administration (RDA), Korea.
  • Ministry of Agriculture and Fishery (MAF), Korea. 2000. Implementation Plan for Environmentally Friendly Agriculture.
  • Ministry of Agriculture and Fishery (MAF), Korea. 2001. Official Fertilizer Standards.
  • National Institute of Agricultural Science and Technology (NIAST), Korea. 1994. Annual Research Report.
  • National Institute of Agricultural Science and Technology (NIAST), Korea. 1997. Annual Research Report.
  • National Institute of Agricultural Science and Technology (NIAST), Korea. 1998-1999. Research Report of Agricultural Environment Monitoring.
  • National Institute of Agricultural Science and Technology (NIAST), Korea. 1999. Annual Research Report.
  • Rural Development Administration (RDA). Korea. 1997. Composting and Utilization of Organic Wastes for the Environmental Agriculture.
  • Rural Development Administration (RDA). Korea. 2000. Effective Management for By-product Fertilizer. Working Report.
  • Rural Development Administration (RDA). Korea. 2001. Guidelines for Official Fertilizer Standards.
  • Sam Hyun Kim. 1999. Inspection of Raw Materials for Composting and Facilities. Working Report, National Institute of Agricultural Science and Technology (NIAST), Korea.

Index of Images

Table 1 Changes in Soil Fertility in Korea

Table 1 Changes in Soil Fertility in Korea

Table 2 Trends in the Use of Chemical and Organic Fertilizers in Korea

Table 2 Trends in the Use of Chemical and Organic Fertilizers in Korea

Table 3 Nutrient Content of Agricultural by-Products (% of DRY Weight)

Table 3 Nutrient Content of Agricultural by-Products (% of DRY Weight)

Table 4 Nutrient Content of Forest by-Products (% of DRY Weight)

Table 4 Nutrient Content of Forest by-Products (% of DRY Weight)

Table 5 Nutrient Content of Livestock Manure (% of DRY Weight)

Table 5 Nutrient Content of Livestock Manure (% of DRY Weight)

Table 6 Nutrient Content of Livestock Manure

Table 6 Nutrient Content of Livestock Manure

Table 7 Nutrients and Heavy Metals in Sludge from Sewage and Water Purifying Plants

Table 7 Nutrients and Heavy Metals in Sludge from Sewage and Water Purifying Plants

Table 8 Chemical Composition of Human Sewage

Table 8 Chemical Composition of Human Sewage

Table 9 Food Waste Production and Treatment

Table 9 Food Waste Production and Treatment

Table 10 Nutrient Content of Food Wastes

Table 10 Nutrient Content of Food Wastes

Table 11 Chemical Content of Organic Sludge from Various Industries

Table 11 Chemical Content of Organic Sludge from Various Industries

Table 12 Categories of Organic Wastes

Table 12 Categories of Organic Wastes

Table 13 Usable Materials

Table 13 Usable Materials

Table 14 Materials That Can Be Used after Examination*

Table 14 Materials That Can Be Used after Examination*

Table 15 Unusable Materials

Table 15 Unusable Materials

Table 16 Inspection Standards for the Usable Materials after Inspection

Table 16 Inspection Standards for the Usable Materials after Inspection

Table 17 Differences between Organic Fertilizer and by-Product Fertilizer

Table 17 Differences between Organic Fertilizer and by-Product Fertilizer

Table 18 Examples of Official Standards for by-Product Fertilizer

Table 18 Examples of Official Standards for by-Product Fertilizer

Table 19 Official Standards for Organic Fertilizer: Some Examples*

Table 19 Official Standards for Organic Fertilizer: Some Examples*

Table 20 Classification of by-Product Fertilizers

Table 20 Classification of by-Product Fertilizers

Table 21 Results of Inspection of Commercial Composts

Table 21 Results of Inspection of Commercial Composts

Table 22 Maximum Levels of Heavy Metals in Imported Compost (MG/KG)

Table 22 Maximum Levels of Heavy Metals in Imported Compost (MG/KG)

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