Food and Fertilizer Technology Center - publications

Nov. 30, -0001

Quality Control for Organic Fertilizers

After years of chemical fertilizer use, many Asian farmers are beginning to return to organic fertilizers, especially for high-value crops such as vegetables and tea. They have found that organic fertilizers make yields more stable, and improve the quality of produce. Applications of organic fertilizers also help control soil-borne diseases, improve soil properties and conserve soil moisture.

In recent years, there have also been developments in the mass production of compost. It is still being made on farms, but increasingly, it is also being made on a large scale in modern factories. These factories use a wide range of raw materials which vary in quality from one batch to another. It is very difficult to standardize and characterize the finished products. However, unless this is done, there is the danger that farmers may be buying substandard products. Farmers also need to know the nutrient content of organic fertilizer, so they can tell how much to apply.

The problem of quality control is a major limitation to the efficient use of compost in modern commercial agriculture.

Problems in Fertilizer Quality

Immature Compost

Compost maturity is an important aspect of compost quality. Immature compost may have an adverse effect on crops for several reasons, including the heat it generates as decomposition proceeds, the nitrogen taken up by microorganisms during the process of decomposition, and the presence of phytotoxic compounds. Several parameters have been developed to determine the maturity of compost.

There are a number of laboratory tests which can be used by commercial compost factories. One of the most common is determination of the C/N ratio. During composting, the content of total carbon decreases while that of total nitrogen increases, resulting in a fall in the C/N ratio. Other properties which give an indication of maturity include cation exchange capacity (CEC), chromatograms of humic substances extracted from the compost, ash content, and the level of volatile gases. However, some of these methods are best suited to particular types of composted materials. None of them can be universally applied with the same degree of success to any kind of compost.

Other parameters do not need expensive equipment for measurement. They can be used by farmers to judge the maturity of the compost they make themselves. These include the color of compost, and its smell and temperature. When after a pronounced temperature rise, compost becomes relatively cool with a stable temperature, it is generally mature.

On some occasions, immature compost may be preferred for some special functions, such as the use of raw compost as an organic herbicide, or for hot beds in mushroom production.

Presence of Toxic Elements

A major problem in compost production is the presence of toxic elements which may be harmful to crop growth and/or human health. Two of the most plentiful sources of raw materials in industrialized societies are municipal wastes and sewage. Both these often contain unacceptably high levels of heavy metals such as arsenic, cadmium and lead. It is very difficult to remove a small percentage of toxic elements from compost, but if they are left in they are likely to contaminate the food chain. Food wastes and other by-products from agro-industrial processing may also contain toxic substances.

Although livestock manure is a rich source of nitrogen, composted livestock wastes have special toxicity problems. Phytotoxic compounds such as volatile fatty acids are produced when animal waste is stored under anaerobic conditions, although they are thoroughly decomposed by aerobic composting. Good aeration and regular turning of the compost pile are thus very important. Livestock manure may also contain high levels of the copper and zinc which are used as additives in livestock feed, especially in pig and poultry production.

The importance of composting as a means of disposing of agro-industrial wastes is often emphasized. However, if the waste disposal aspect becomes too important, unsuitable materials may be used. Most organic fertilizer factories in Asia are fairly small, and many suffer from financial difficulties. Several surveys of compost quality in Asian countries have found that as much as a third of the compost products sold did not meet minimum standards.

Usually, the inferior products simply contained too little organic matter or nitrogen. They did not do crops much good, but they did not do them much harm either. However, a significant number of the substandard compost products had high concentrations of heavy metals. There were even a few cases of compost which contained toxic substances such as petrochemical wastes. Instead of promoting crop growth, they ruined it!

Regulations on Compost Quality

Most of the compost used in the region is made by farmers on their own farms, from crop residues, livestock wastes and other farm by-products. Since farmers are in control of what goes into the compost, there seems no need to regulate their compost production for their own use. It is commercial compost production that needs to be regulated.

Most Asian countries have some form of government control over commercial compost production, although the form it takes varies from one country to another. In Japan, regulations governing compost limit only the maximum permitted levels for potentially dangerous elements such as cadmium, mercury and arsenic. For other qualities, the Japanese Government has adopted guidelines, rather than regulations, for quality control.

Most other counties have regulations to cover the production and sale of commercial composts. These regulations are often very complex, because commercial compost is made from such a wide range of very different materials - bark, livestock manure, bone meal etc. Fertilizer regulations in Taiwan, for example, classify organic fertilizers into 25 categories, depending on the type of raw materials used.

Most regulations cover the nutritional values of compost. In the Philippines, an organic fertilizer must contain a minimum of 7% nitrogen. Composted products with less than 7% N must be sold as soil conditioners, rather than as fertilizer. Most countries also have regulations which cover the organic matter content.

All countries also limit the content of heavy metals such as mercury and cadmium in compost, although the actual permitted levels vary from country to country.

Quality Control

Monitoring of Quality

Whether guidelines or regulations are the official safeguards of quality, these will only be observed if there is regular monitoring. In fact, without monitoring, regulations have little meaning.

Sometimes fertilizer companies carry out their own monitoring. More often, there is some government department or official body which is responsible for the scientific analysis of compost samples. Often the collection of samples is done by local government officials, rather than the fertilizer factories themselves. This is to ensure that sampling is fair and adequate.

Labeling of Bags

Another basic requirement to maintaining compost quality is that bags of commercial compost should carry clear and informative labels. Good labeling of bags enables the consumer to compare different brands of compost in terms of their nutrient content and other qualities, and not just in terms of their price. It also helps protect consumers from products made by substandard compost factories.

Participants at a recent FFTC Workshop agreed that the following information should be recorded on the bags of compost offered for sale.

  • Nutrient content

  • C/N ratio (generally less than 20)

  • Organic matter content (generally more than 60%)

  • Moisture content (generally set at less than 35%)

  • pH

  • EC

  • % inert materials (gravel, plastic etc. This should be limited by regulations).

It was also suggested that bags containing compost should show the duration of the composting period. This is because criteria such as the pH, which should indicate maturity, can be adjusted artificially. Labels on organic materials sold as compost could thus indicate satisfactory levels of pH, EC and so on, without the materials ever having passed through a proper composting process.

It was also agreed that the following criteria should be used by producers for quality control, although they need not be recorded on the bag.

  • Heavy metals such as zinc, lead and mercury (maximum levels to be covered by regulation).

  • Germination tests. (The use of these should be recommended rather than regulated).

  • Temperature stability. (This should be used by the producer as a measure of compost maturity).

Because of the variable materials used in composting, all these criteria should be shown as within a particular range, rather than as a specific quantity.

FFTC International Workshop

Quality Control of Organic Fertilizers (Compost)

: Suweon, Korea

June 23-28 1997

No. participating countries
: 7 (Japan, Korea, Malaysia, Philippines, Taiwan ROC, Thailand, U.S.A.)

No. papers:

No. participants:
50 (plus observers)

: Rural Development Administration (RDA), Korea

List of Paper

1. Potential of organic waste compost utilization in vegetable crop production systems

- Peter Stoffella

2. Preparation and maturity evaluation of composts

- Shang-Shyng Yang

3. Quality control and evaluation of animal waste compost

- Yasuo Harada

4. Quality control of commercial organic fertilizers in Korea

- Youn Lee

5. Evaluation of efficient utilization of organic materials based on their decomposition pattern in soils

- Hitoichi Shiga

6. Effects of organic fertilizers on soil improvement, yield and quality of speciality crops in Taiwan

- Mu-Lien Lin

7. Effect of compost on soil improvement, yield and quality of crops

- Sang-Kyu Lee

8. The IBS rapid composting technology: Its role in producing good quality organic fertilizers in the Philippines

- Virginia C. Cuevas

9. Organic sources for vegetable cultivation in Malaysia

- P. Vimala

10. Production and application of compost for soil improvement in Thailand

- Prachya Dhanyadee

Index of Images

Figure 1 New Compost Pellet Developed in Japan

Figure 1 New Compost Pellet Developed in Japan

Figure 2 Compost Extruder for Pellet Production

Figure 2 Compost Extruder for Pellet Production

Figure 3 Grape Injured by Commercially Sold Compost Containing Toxic Substances

Figure 3 Grape Injured by Commercially Sold Compost Containing Toxic Substances

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