Raw Materials Used for Composting

CHONG-HO WANG, YU-WEN LIN, WEI-TEN HUANG, and LI-RONG CHIU, 2005-12-01

4.1 Introduction

Large amounts of agricultural by-products or livestock wastes are produced annually in Taiwan (Table 1). Hogs excrete about 73 x 10⁴mt/year; chickens, 186 x 10⁴mt/year; and cattle, 30 x 10⁴ mt/year. Annually, by-products from bagasse amount to 31 x 10⁴ mt; straw, 31 x 10⁴mt; rice husk, 1.7 x 10⁴mt; bark, 5 x 10⁴mt; fruit and vegetable, 7 x 10⁴mt; mushroom, 5 x 10⁴mt; and coconut, 0.5 x 10⁴mt (Huang and Lin 2001). Composting agricultural wastes and recycling them on arable lands have been widely adopted to lessen the pressure on landfills and conserve natural resources. Thus, the use of organic materials containing essential nutrients for plants reduces importation of chemical fertilizers and their manufacture.

The Taiwanese government has heightened its advocacy on recycling organic wastes, including livestock manure, in agricultural fields. However, composting organic wastes in a farmhouse has been difficult because of shortage of labor and raw materials (Fig. 1). Commercialized composting is quite popular in Taiwan, and the material resources are mainly from livestock manure.

This paper discusses the various raw materials for composting, their benefits and drawbacks, and the techniques of composting, mixing together different raw materials to achieve a better balance.

4.2 Kinds and Sources of Main Organic Materials

Organic materials in Taiwan may be classified into eight categories on the basis of their origin, as follows: crop residues, green manure, common compost, mushroom compost, animal manure (cattle, swine, and poultry), municipal refuse, residues after oil extraction, and residues from processing animal products. The nutrient contents of these materials differ greatly. The quantity of each organic waste category is shown in Table 2 (Hsieh and Hsieh 1990). The total amount of these major organic wastes is estimated up to 1,878 × 104 mt per year (Table 2). Some wastes such as rice straw, with a high C:N ratio of more than 20, can be considered a good source of carbon, but other wastes like animal manure with a low C:N ratio of less than 15 can be considered a primary source of nitrogen (Wang 1989).

The daily average excretion of cattle (27.5 kg/ head) was the highest, followed by swine (0.85 kg/head), then poultry (0.12 kg/head) (Table 3). According to Yen (1989), the nutrient content of poultry manure is much higher than that of swine or cattle manure (Table 4). Assuming the N, P2O5, and K2O content of daily excretion of livestock as shown in Table 5, the total amounts of nutrients in the manure of swine, cattle, and poultry in Taiwan were estimated to be 108,555 mt of N; 121,113 mt of P2O5; and 87,711 mt of K2O. These quantities were equivalent to 45.5% N; 173.7% P2O5; and 90.1% K2O of the chemical fertilizers used in 1987 in Taiwan (Table 6). Chang (1995) also reported that assuming the N, P2O5, and K2O contents of the daily excretions of livestock as shown in Table 5, the total amounts of nutrients in the manure of swine, cattle, and poultry in Taiwan were estimated to be 15.20 x 104 mt of N; 17.19 x 104 mt of P2O5; and 11.57 x 104 mt of K2O. These quantities were equivalent to 58% N, 233% P2O5, and 110% K2O of the chemical fertilizers used in 1987 in Taiwan (Table 7).

4.3 Chemical Composition of Organic Wastes

Samples of crop residues; used mushroom compost; common compost; green manure; municipal wastes; swine, cattle, and poultry manure; residues after oil extraction; and animal by-products in Taiwan were analyzed for the chemical composition of their nutrient contents (Tables 8-14).

4.3.1 Crop Residues

Rice straw, rice hull, and other straws of graminaceous crops with abundant fibrous materials usually have a high C:N ratio, with a low nitrogen content but fairly high potassium and silica contents (Table 8). Potassium and silica help improve the resistance of crops to disease and lodging, and fibrous materials provide an energy source for soil microorganisms as well as improve and condition soil physical properties (Fig. 2). Crop residues are used as mulches to cover the surface of the soil and help maintain favorable soil moisture content and temperature as well as prevent the accumulation of salts or the multiplication of weeds on the soil surface (Fig. 3). These materials can well be combined with swine or poultry manure that has a high nitrogen content to make better compost for crops (Lin et al.) (Fig. 4).

4.3.2 Green Manure

Leguminous green manure crops are an important source of natural nitrogen. They fix nitrogen from the air and at flowering stage are usually incorporated into the soil, about ten days before planting the main crop. In extensively cropped areas, green manure crops are of great value to farmers since they reduce fertilizer costs. In intensively cropped areas, they may compete with the main crop for land. However, even in areas with very intensive multiple cropping systems like in Taiwan, some farmers are still growing Sesbania sesban or Crotalaria juncea as a green manure crop in summer, and Berseem clover, milk vetch, and rape in the winter fallow season before planting the main crop like rice, corn, and sorghum. The chemical composition analysis of these green manure crops is shown in Table 9. These green manure crops that have low C:N ratio (lower than 20 at vegetative stage) can be considered primary sources of nitrogen (Fig. 5).

4.3.3 Used Mushroom Compost

With the rapid development of the mushroom industry, used mushroom compost has become a good source of organic manure in Taiwan in recent years. Such compost consists mainly of sawdust (Fig. 6) and added with materials such as limestone and rice bran. Used mushroom compost has low potassium content as a result of leaching losses during mushroom culture, but the phosphorus, calcium, and C:N ratio and organic matter contents remain high (Table 10 and Fig. 7). Also, used mushroom compost has a high fibrous material content which improves soil physical properties and biological activity. However, the remnant mycelia in these materials may sometimes have a harmful effect on the roots of some crops. Therefore, it is recommended that used mushroom compost should be combined with a proper amount of high-nitrogen manure such as swine or poultry manure or oil extraction residues and be well fermented to kill the mycelia, before applying to the soil (Fig. 8).

4.3.4 Animal Manure (Cattle, Goat, Swine, Chicken)

The nutrient content of swine manure is slightly higher than that of cattle manure, but with a higher copper content (Table 11) and lower content of fibrous material, discouraging repeated, long-term applications of this manure (Fig. 9). It is best to dilute this manure by mixing it with rice hull, sawdust, rice straw, and similar fibrous materials and fermenting it before use.

The nutrient content of chicken manure is much higher than that of swine manure (Table 11). However, its higher content of zinc and antibiotics and lower content of fibrous material discourage direct applications of fresh poultry manure to the soil. The best way to utilize this manure is to mix it with cattle and swine manure, rice straw, rice hull, sawdust, and other fibrous materials, and ferment it thoroughly before use.

Cattle manure has a reasonably high content of nitrogen, potassium, and fibrous materials. It is good animal manure because it does not have heavy metals and antibiotics in it (Table 11). Repeated applications of this manure to the soil can be recommended, but phosphorus should be supplied from other sources to make up for its shortage in this manure. Nutrient content of goat manure is slightly higher than that of cattle manure (Table 11).

4.3.5 Residues from Oil Extraction

Oil extraction residues from oil seeds generally have high nitrogen content and low level of carbonaceous material (Table 12 and Fig. 10). Liberal applications of this material to the soil may greatly promote the growth of a crop's vegetative parts. However, crops given this treatment are usually weak and easily attacked and damaged by plant pests and environmental stresses. As well, applying these residues to the soil when they are still fresh often attracts large numbers of soil-borne insects, which may also harm the crop. It is best to mix these seed residues with rice hull, sawdust, mushroom compost, bone meal, oyster shell, among other things, and fully ferment the compost before use.

4.3.6 Residues from Processing Animal Products

The nutrient contents of animal residues differ greatly according to the type of residue (Table 13). Animal blood, meat, horn, feet, wool, and feathers can all be used as a source of nitrogen fertilizer since they all have very high nitrogen content. Oyster shell and eggshell are good sources of calcium and bone meal can be a good source of phosphorus. However, all of them are very low in potassium. Fur should not be used in composting because of its high chromium content that can easily accumulate in the soil, causing toxicity in crops.

4.3.7 Reasons for Composting Agricultural Waste for Fertilizer Use

Composting improves the physical characteristics of agricultural wastes.
It lowers the C:N ratio, thus avoiding the nutrient competition between plants and microorganisms. Because agricultural wastes contain relatively less nitrogen, they inhibit the growth and reproduction of nitrogen-loving microbes.
It lowers the volume of waste by four-fifths its original volume.
It sterilizes, because of high temperatures during composting, weed seeds, germs, and pests in agricultural wastes, reducing the cost of production and disease and pest control.
It minimizes poor aeration problems. When directly applied without composting, agricultural wastes may exude toxic substances such as H2S, organic acids, and phenolic compounds and gas of methane and N2O.

4.3.8 Advantages of Composting Agricultural Wastes

Composting lessens pollution impact on environments.
It boosts soil fertility, improving both the biological and physicochemical properties of the organic material.
It allows the utilization of essential nutrients from agricultural wastes in growing crops.
It aids the use of slow-release fertilizers, particularly its nitrogen content, which after one-third is used, becomes slow-release humic nitrogen.
It has a growth-promoting humic substance or phyto-hormone that accelerates root development.
It increases and diversifies the microbe phase, reducing pathological and pest incidence.
It minimizes nutrient loss as negatively charged organic material maintains and holds nutrients.
It produces humic substances (humates) with high buffering capacity for better soil management.

4.4 Conclusion

Because of their multiple roles in improving the physical, chemical, and biological properties of soil, organic materials are very important in maintaining soil fertility. However, organic materials per se cannot give the full range of soil benefits. Some carbonaceous organic materials such as rice straw, corn stalk, rice hull, and sawdust are very useful in improving the physical and biological properties of soil, but they are very slow in releasing nutrients like nitrogen, phosphorus, and potassium. Some nitrogenous organic materials such as residues left after oil extraction and swine and poultry manure are high in nitrogen, phosphorus, and potassium but have little impact on improving soil physical properties. A proper combination of carbonaceous and nitrogenous organic materials makes an ideal compost or an effective and complete fertilizer. Furthermore, because some organic materials contain harmful mycelia, antibiotics, plant pests, and excessive level of heavy metals, proper mixing and composting, leading to dilution and sterilization, may greatly promote the quality of organic materials.

4.5 References

Chang S.S. 1995. Research and development in the appropriate use of organic materials for crop productions current status and perspective. pp. 1-14. In: Taiwan Agricultural Research Institute (ed.), Proceedings of the Conference on Rational Application of Organic Fertilizer.
Huang S.N. and C.C. Lin. 2001. Current of organic materials recycling in southern Taiwan. pp. 14-24. In: Food and Fertilizer Technology Center for Asian and Pacific Region (ed.), Proceedings of the International Workshop on Recent Technologies of Composting and Their Applications.
Hsieh, S.C. and C.F. Hsieh. 1990. The use of organic matter in crop production. 315:1-19. Taiwan, ROC: Taichung District Agricultural Improvement Station.
Lin, Y. W., T. S. Liu, and C. H. Wang. 2003. Study on nitrogen mineralization characteristics of organic materials. J. Agric. Res. China 53:178-190.
Wang, H.H. 1989. Utilization of agricultural wastes in organic farming. Organic Farming, special publication 16:217-227. Taiwan, ROC: Taichung District Agricultural Improvement Station. (In Chinese).
Yen, S.C. 1989. Utilization of animal wastes in organic agriculture. Organic Farming, special publication 16:229-242. Taiwan, ROC: Taichung District Agricultural Improvement Station. (In Chinese).

Index of Images

Table 6 Total Amount of N, P2O5, and K2O in Swine, Poultry, and Cattle Manure in Taiwan, 1987.
Figure 1 Composting Organic Fertilizers in a Farmhouse Is Difficult Because of Shortage in Labor and Raw Materials.
Figure 2 Crop Residues Usually Have Low Nitrogen Content, but Fairly High Potassium and Silica Content, and a High C/N Ratio: A) Rice Straw; B) Crushed Rice Hull; C) Peanut Hull; D) Coconut Shell.
Figure 3 Crop Resides Are Used to Cover the Surface of the Soil; These Materials Are Good Mulches Which Help Maintain a Favorable Soil Moisture Content and Temperature, and Prevent the Accumulation of Salts or the Multiplication of Weeds on the Soil Surface.
Figure 4 Crop Residues Can Well Be Combined with Swine or Poultry Manure with High Nitrogen Content, to Make Better Compost.
Figure 5 Green Manure Which Has a Low C/N Ratio of Lower Than 20 at Vegetative Stage, Can Be Considered Primarily As a Source of N: A) Sesbania Sesban; B) Crotalaria Juncea; C) Berseem Clover; D) Rape.
Figure 6 Mushroom Compost Made up Mainly of Sawdust.
Figure 7 Used Mushroom Compost Has Low Potassium Content As a Result of Leaching Losses during Mushroom Culture, but Phosphorus, Calcium, and C/N Ratio and Organic Matter Contents Remain High.
Figure 8 Used Mushroom Compost Should Be Combined with a Proper Amount of High-Nitrogen Manure Such As Swine or Poultry Manure or Residues after Oil Extraction, and Should Be Well Fermented to Kill the Mycelia, before It Is Applied to the Soil.
Figure 9 The Direct Application of Fresh Poultry Manure to the Soil Is Discouraged Due to Its High Content of Zinc and Antibiotics, and Low Content of Fibrous Material.
Table 1 Estimated Amounts of Organic Wastes Produced in Taiwan, 1999.
Figure 10 Residues from Oil Seeds after Oil Extraction Generally Have High Nitrogen Content and Low Level of Carbonaceous Material.
Table 2 Estimated Quantity of Major Organic Wastes Produced in Taiwan.
Table 3 Daily Average Excretion of Swine, Poultry, and Cattle.
Table 4 Average Content of N, P2O5, and K2O in Fresh Manure of Swine, Poultry, and Cattle.
Table 5 Daily Excretions of N, P2O5, and K2O of Swine, Poultry, and Cattle (Unit: G/Head/Day).
Table 7 Estimated Environmental Loadings of N, P2O5, and K2O Coming from Chemical Fertilizer Consumptions and Animal Excretions in Taiwan, 1994 (10 Kton).
Table 8 Chemical Analysis of Crop Residues (DRY Matter Basis).
Table 9 Chemical Analysis of Green Manure Crops (DRY Matter Basis).
Table 10 Results of Chemical Analysis of Mushroom Culture Wastes (DRY Matter Basis).
Table 11 Results of Chemical Analysis of Animal Manure (DRY Matter Basis).
Table 12 Chemical Analysis of Residues Left after Oil Extraction from Various Oil Seeds (DRY Matter Basis).
Table 13 Chemical Analysis of Residues from Processing Animal Products (DRY Matter Basis).