Chapter 5 Basic theories of composting technology – Matters requiring caution
5

Basic theories of composting technology – Matters requiring caution

This chapter discusses on “pH,” “carbon-nitrogen ratio (C/N),” “aeration volume,” “cutback frequency,”“form (and size) of raw materials,” “void ratio,” “volume weight (specific gravity),” and “fermentation
process,” which are matters that have not yet been mentioned, among the matters that require caution whensmooth composting is attempted. Also, leftover foods, or the so-called food wastes, contain salt and oil
used in cooking, and effects of these substances are also considered.
5.1

pH

The optimum range of pH values for composting is between about 4 and 9, and microorganisms remain
active and satisfactory aerobic fermentation continues in the range.
The moisture content of raw garbage, the source material of composting, is normally as high as 80%, andfor this reason organic acids might be generated in an anaerobic environment that could result while raw
garbage is being discharged, stored, collected and transported. However, the pH value of raw garbage isusually at around 4 to 6, so problematic situations are not likely to arise. However, citrus fruit juice is low
in the pH value (the pH of lemon juice is about 2), and the pH value of compost could fall below 4 if alarge amount of citrus fruits waste were mixed. If the pH fell to such a low value, activities of
microorganisms are hindered. Organic acids are also organic substances decomposed by microorganisms,
but a long time would be needed for decomposing organic acids.
The following diagram shows the progress of fermentation, represented by a change in the temperature,when the pH value of seed compost is near the neutral state and when it fell below four because lactic acidwas generated. Decomposition of raw garbage slowed down when the pH value was low.

Temperature of seed compost (°C)

There are two ways to promptly resolve the low pH situation.

Change in temperature during raw garbage composting
Around pH 7
pH 4 orlower

Fig. 5-1: Progress of raw garbage composting and pH value

1© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
5.1.1

Utilizing returned compost

When aerobic fermentation is progressing, a balance is maintained between the ammonium generation
caused by decomposition of amino acids and proteins and the nitrification (NH4+ → NO3-) that progresses
as the temperature changes during raw garbage composting, and the compost is kept in a mildly alkali state.
Returned compost is used in composting process for moisture content adjustment and for adding
microorganisms, which also helps adjusting the pH value to be within the optimum range.
5.1.2

Adding alkali agent

No returned compost is available when a compost center just started operation. Sometimes returned
compost alone cannot adjust the pH value to the optimum range, when a large amount of leftover citrus
fruits is composted. In such cases, lime and other alkali agents are added for adjusting the pH value to bewithin the optimum range. However, if the alkali agent was insufficiently mixed, the alkali level might rise
locally to an extremely high value at some portion of the compost, so attention is needed on the mixing
state. The reactivity also requires attention to some types of alkali agents. The pH value could rise above
the optimum range with time, even if the adjustment was intended to bring the pH value to the optimum
range.
5.1.3

Sludge composting

When using sludge as the raw material of composting, attention is needed on a high pH value that could
result. Lime is sometimes added as a dewatering aid when making sludge, which could raise the pH value
to 10 or higher. It is necessary to lower the pH value to around 8 or 9, and the addition of returned compost
is an effective method. Another method is adding organic citrus acid.
5.2

Carbon-nitrogen ratio (C/N)

5.2.1

C/N during composting

Since composting is promoted by activities of microorganisms, the following items would be necessary: thesource of energy for keeping the microorganisms active; and the components that enable them to form thecell bodies as they proliferate. An index for showing the situation is carbon-nitrogen ratio (C/N). The
carbon contained in organic wastes is consumed in the following ways: as energy for activities of
microorganisms and discharged as a part of carbon dioxide; and taken into the body of microorganisms
along with the nitrogen contained in the organic waste, for forming proteins that lead to the proliferation of
microorganisms.
In the process, the balance between carbon and nitrogen is important. When the C/N is high, there is plentyof energy for activities but the growth of microorganisms would be limited. Under the circumstances, asmall number of microorganisms works hard for decomposing the organic substances, which prolongs thecomposting period. On the contrary, when the C/N is low, the amount of energy for activities is small
compared to the number of microorganisms, and in addition the growth of microorganisms would also be
limited. As a result, mineralization of nitrogen progresses and a large amount of NH4+ is generated that2

© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
raises the pH value. Consequently, NH3 is formed that emits a strong ammonium odor, and the nitrogencomponents that should remain in the compost as a fertilizing component become dispersed.
The C/N fit for composting is about 20 to 30, and composting would progress smoothly by adjusting theC/N of organic wastes to be within the above range. In the case of woody wastes with rather high C/Nvalues between around 100 and 1,000, materials that contain a large amount of nitrogen, such as livestock
manure, is added to adjust the value to about 40. In some cases, urine and other types of chemical fertilizer
are added.
The C/N is within the range between 20 and 30 for most raw garbage, so no adjustment is necessary.
However, the C/N might decline as composting progresses and a strong ammonium odor might be emitted.
In such a case, the cutback frequency should be raised or the aeration volume increased, for promoting
nitrification of ammonia. (NH4+ →NO3-)
When the C/N is below 20, a large amount of ammonium would be generated because the nitrogen content
is large, and nitrification of ammonia alone cannot eliminate the ammonium odor. A material with a large
carbon content should be mixed for adjusting the C/N to an appropriate level, before composting.

Table 5-1: C/N of raw materials of compost (examples)
Materials

C/N

Materials

C/N

Cattle manure

15-25

Orange juice dregs

45

Porcine manure

10-15

Oil dregs

6-10

Poultry manure

6-10

Rice hull

70-80

Raw garbage

10-25

Rice straw

50-60

Rice bran

20-25

Barley straw

60-70

Beer lees

8-10

Mown hay

10-30

Coffee grounds

15-20

Pruning wastes

60

Cocoa refuse

15-20

Fallen leaves(coniferous trees)

40-60

Fishes and meats

6-10

Fallen leaves(broad-leaved trees)

15-40

Vegetable scraps

10-25

Bark

500 or higher

Tea leaf dregs

10-15

Sawdust500 or higher

3© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution

Low

High
Green Waste

Sawdust

Rice
straw

Livestock
manureFermentation is
promoted byadjusting C/N ratio

Rice branRawgarbagePruningand otherwastesContaining large
amount of carbon (C)Returned compost
Nitrogen fertilizer
Containing large
amount of nitrogen (N)Compost with agood C/N balance

Fig. 5-2: Satisfactory fermentation and high-quality composting from a viewpoint of C/N

5.2.2

C/N of compost product

The C/N value appropriate for compost products is between 10 and 20. However, 35 or less would besatisfactory if a raw material with a high C/N value, such as bark, was used. In such a case, compost with a
low C/N value or a nitrogen fertilizer should be added when applying the compost as a fertilizer, or an
application method that mainly targets at soil improvement should be adopted for the compost.
After spreading compost on the ground, microorganisms in the soil and in the compost start activities
vigorously, feeding on the compost as a source of nutrients. In the process, two-thirds of carbon containedin the compost is consumed as energy for activities of microorganisms, and carbon dioxide is discharged in
respiration. The remaining one-third is taken into the bodies of microorganisms, and used for their growth.
The C/N of microorganism bodies is about 6.7. For example, if compost with the C/N value of 20 was
applied on the ground, 13.3 parts of the carbon are consumed for respiration and the remaining 6.7 parts areused for proliferation of the microorganisms. As a result, the C/N value would be 6.7, which is the same as
the microorganism bodies. Next, let us examine a case of compost product with the C/N value of 40. 22.6
parts of the carbon are used for respiration and the remaining 13.4 parts are used for proliferation of the
microorganisms, but the nitrogen is deficient for proliferation of the microorganisms. As a result, themicroorganisms start consuming nitrogen in the soil that should be used by the plants or attack the roots ofthe plants for obtaining nitrogen components, affecting the plant growth adversely. Such a phenomenon isreferred to as “nitrogen starvation.”

4© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution

If the C/N value of the compost laid on the ground is appropriate, nitrogen necessary for plant grown would
be discharged.

When the C/N value is too high, nitrogen starvation might result.
Fig. 5-3: Impacts of C/N of compost on plant cultivation

5.3

Aeration

5.3.1

Aeration using a blower (forced aeration)

Aerobic fermentation may be promoted efficiently, through mechanical aeration. Composting could
progress rapidly with raw garbage and cattle manure, which are easily decomposed organic substances. The
temperature would exceed 70℃ in a short period of time (in a day, for example). As a result, the waste
loses the filthy feature promptly, and generation of odors could be suppressed.
Aeration may be performed continuously by operating a fan continuously, or intermittently by operating a
fan for an hour and halting the operation for two hours, for example. When the aeration volume increases,
the amount of heat dissipation also increases. Under the circumstance, rising of the temperature andmaintenance of high temperature would be prevented. As such, the aeration volume is adjusted bycontrolling the number of rotations of the fan or changing the operation time of the fan. When the moisture5© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
content is only slightly high, the moisture content is sometimes adjusted by increasing the aeration volume
to promote evaporation of the moisture, instead of mixing a dry auxiliary material.

Photograph 5-1: Fan for aeration

Photograph 5-2: Aeration pipe

For example, when composting a waste containing cattle manure that has been piled to a height of 1 m or
greater, an aeration volume of 100 liters/min-m3 or more is adopted in many cases, taking into
consideration the electric charge and other costs also.
As can be seen, the aeration volume is not determined uniformly, but needs to be adjusted to suit theproperties of composting materials and the situation of composting. For promoting uniform composting,cutback (agitation) is also necessary in addition to aeration.
No aeration or cutback (agitation)
 Composting would not progress.
 Anaerobic state results inside, and odors
are emitted.

Aeration is performed
 Aerobic fermentation is promoted
efficiently and the temperature rises.
 However, excessive aeration could lower
the temperature and spoil the effect.
 Cutback (agitation) should be performed
for promoting uniform composting.
 Cutback may be performed manually also.

Or

Fig. 5-4: The necessity of aeration

6© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
The following diagram shows an example of change in the temperature during composting. Satisfactoryfermentation resulted when aeration and cutback were performed appropriately. However, composting is
not promoted at all if wastes were merely piled up.
Change in compost temperature (example)

Fermentation temperature (°C)

Cutback

Aeration and cutback

Piling-up only

Time (weeks)

Fig. 5-5: Progress in composting and change in temperature

5.3.2

Cutback (agitation)

For mechanical aeration, facilities need to be introduced and electric energy is necessary for operating fans,which would raise the costs. An alternative method is to perform cutback (agitation) using a shovel loader
or by manpower. Frequent cutback is necessary for supplying a sufficient amount of oxygen, but loweringof the temperature and increase in the staff’s workloads would result. In reality, cutback is being performed
once a day or once every two days in most cases.

Cutback using a shovel loader

Manual cutback

Fig. 5-6: Compost cutback methods

5.4

Form of raw materials

In order to promote aerobic fermentation, microorganisms need to come in contact with the surface of raw
materials efficiently, and a sufficient amount of oxygen needs to be supplied. For the purpose, it is effective
to crush raw materials to a particle size of about 1 cm. On the other hand, particles with a too small

7© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
diameter or of a form without much thickness prevent voids from being secured in the mixture, whichhinders air permeability. In such a case, auxiliary materials that are solid in the form, such as rice hull,
sawdust, rice straw and barley straw, should be added for enhancing the air permeability.
In a piled-up composting method in which a mixture of raw materials and auxiliary materials is piled up to
about 2.0 m in the height, voids in the bottom part tend to get crushed, pressurized by the self-weight of thematerials. Also, water tends to gather at the bottom part due to the gravity and the moisture content tends torise in the portion. Therefore, the moisture content needs to be managed carefully to keep it rather low(about 40 to 50%), so that aerobic fermentation would continue.
5.5

Void ratio and bulk density (specific gravity)

Void ratio and bulk density are correlated, and the higher
the void ratio of a mixture, the smaller the specific gravity
would be for the same mixture. Bulk density may bemeasured easily by filling the mixture in a container of aknown volume and then measuring the weight, as shownin the photograph. By adjusting the bulk density at thestart of composting to a value as close as possible to
500 g/liter, the air permeability would improve, thefermentation would start smoothly and the temperature

Photograph 5-3: Void ratio is being
managed by measuring specific gravity

would rise promptly.
The voids at the bottom part would be pressurized and get crushed, if the compost was piled up too high. Ifaeration is scheduled to be performed only by cutback, the height of the piled mixture should be kept at
1.5 m to 2 m or lower.
5.6

Impacts of salt content

Salt content is not a problem for composting, unless a large amount of waste of high salt concentration(salted and pickled vegetables, miso paste, etc.) is mixed. The fact that raw garbage composting has been
attempted in diverse areas and the compost produced is being used widely evidences that salt content is not
a problem. However, there is a concern that salt (sodium chloride) contained in compost products might
adversely affect plant growth. There are reports that state the recommended limit of salt content in compost,in the form of NaCl, is 5% or less.
When dissolved in water, sodium chloride separates into Na+ (sodium ions) and Cl- (chloride ions). There
could also be nitrate nitrogen (NO3-) and potassium (K+) ions, which are fertilizing components, that havedissolved in water, in addition to the ions of sodium chloride. And too many ions (that raise the electric
conductivity) could adversely affect plant growth. For example, the germination ratio of Japanese mustard
spinach seeds could decline. Lowering of activities of soil microorganisms has also been reported. NaClmeasurement requires labor and takes time, and needs to be conducted at an analysis center. As such, the8© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
salt content is being managed at composting sites based on the electric conductivity, which enables
evaluation that encompasses NaCl.
The electric conductivity (EC) of cattle manure compost is managed to be 5 mS/cm or less, and the value
has been adopted as the quality management value for compost in many cases. Also, high electric
conductivity (EC) causes the germination ratio of Japanese mustard spinach to decline. For this reason,
management is being conducted in some cases in a way that ensures the germination ratio of 80% or higher
to be obtained in a germination test.
There is a point of caution here. Since ionized substances are found in a dissolved state in water, theirimpacts on plants differ depending on the amounts of rainfalls and sprinkled water. The electric
conductivity in soil could rise when plants are grown in an area with extremely small rainfalls, or in aplastic greenhouse or a pot on which the sprinkled (inundated) amount of water is limited. This means thateven compost with the electric conductivity of 5 mS/cm or less that ensures germination ratio of 80% or
higher of Japanese mustard spinach could adversely affect plant growth. The opposite is also true, andcompost with high electric conductivity could make plants grow without hindrance if the rainfall is large in
the area or a sufficient amount of water is sprinkled. Compost made from raw garbage should basically be
used in open-field cultivation, because the salt content is likely to be high.

Plant growth could be affected adversely if the electric conductivity of the soil is highFig. 5-7: Attention is required not only on the salt content of compost but also on the electric conductivity

9© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
5.7

Impacts of oil content

Oil content (fat) is among the substances decomposed in the first stage of composting process, and falls
under the category of easily decomposed organic substances. Comparing plant-derived oil/fat that takes aliquid form with animal-derived oil/fat of a solid form, the plant-derived oil/fat spreads more widely in thecompost and is therefore decomposed more promptly. Spreading of the animal-derived oil/fat is facilitatedwhen the temperature rises, so higher fermentation temperatures are more advantageous for promoting
decomposition.
A test was conducted on Japanese mustard spinach grown in a pot using raw garbage compost added withedible oil. The following was stated, evaluating the test results: “There is a concern that compost withremnant

oil/fatcould

suppressgermination and cause a delay inmineralization of nitrogen that could
hinder plant growth. An index showing
the progress of decomposition of oil/fat isthe pH value. The oil/fat content isextremely small if the pH value of thecompost was 7 or more, and adverse

pH 7-9effects caused by oil/fat content isbelieved to be negligible when the pH
value is 8 or more.”
Fat is decomposed into H2O and CO2 if<pH 7 (acidic)

Fig. 5-8: Oil and fat are favorite foods ofmicroorganisms; the pH value would be 7 to 9 if
decomposition of oil and fat progressed well, and thecompost would be acidic if notsatisfactory aerobic fermentation is underway. When decomposition is not sufficient, the compost would beacidic because organic acids remain as metabolites. This is consistent with the comment indicated above,that “If satisfactory aerobic fermentation progresses, a balance would be maintained between the generationof ammonia resulting from decomposition of amino acids and proteins and the nitrification of ammonia(NH4+ → NO3-), and the compost becomes alkali mildly.” In short, oil and fat are decomposed to a statethat would not adversely affect plants, if satisfactory fermentation progresses.
5.8

Fermentation processes during composting

Even though the fundamental concept of composting has been shared by those involved with composting,there is no unified view on how the fermentation process may be divided. In addition to the “primary
fermentation and secondary fermentation” mentioned above, some say there are the “first stage, second
stage and third stage” while others mention the “premature compost, mildly matured compost, and fully
matured compost.”

10© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
5.8.1“Primary fermentation and secondary fermentation”

The decomposition process of organic substances is divided into the phase during which a large amount offermentation heat is generated and the phase during which the fermentation heat generation calms down
and is stabilized.
(1) Primary fermentation:
Easily decomposed organic substances are mainly decomposed rapidly, generating a large amount offermentation heat and raising the temperature.
(2) Secondary fermentation:
Decomposition and humification of decomposable organic substances progress and are stabilized.
Fermentation is generally deemed as having shifted to the secondary fermentation from the primary
fermentation when the primary fermentation lasted for two weeks or more and the temperature of thecompost no longer exceeds 50℃.
(Sometimes the shift is deemed to have occurred when two weeks or more of fermentation period has
elapsed in the primary fermentation facility and the temperature of the compost no longer exceeds 65℃.
However, compost is sometimes shipped as a product after going through the primary fermentation only.
For this reason, 50℃ is adopted here to ensure that composting has progressed and the product temperature
is sufficiently low.)
5.8.2“First stage, second stage and third stage”

The stages of decomposition of organic substances are represented based on the changes in microorganisms
involved with the fermentation.
(1) First stage:
This is the stage in which easily decomposed organic substances are decomposed. Bacteria and filamentous
fungi are vigorously active as dominant species, utilizing easily decomposed organic substances. As such,oxygen needs to be supplied appropriately, and a surge in the temperature is observed.
(2) Second stage:
This is the stage in which hemicellulose and cellulose are decomposed. The high-temperature steam
generated in the first stage steams the hemicellulose and cellulose, facilitating their decomposition. In theprocess, thermophilic and aerobic ray fungi decompose the hemicellulose that protects the cellulose, andanaerobic cellulose decomposing bacteria decompose the cellulose. Other bacteria and filamentous fungialso decompose the cellulose. The fermented mixture becomes dark brownish in color.
(3) Third stage:
This is the stage in which lignin is decomposed. Basidiomycetes (mushrooms) slowly decompose lignin
over a long period, lowering the temperature of the compost gradually. Bacteria that are active in normal
temperatures are activated as the temperature falls, and diverse microorganisms start proliferating. The
11© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
compost is blackish in color and feels dry. Sometimes white-colored molds and ray fungi proliferate in
portions close to the surface of the compost.
5.8.3“Premature compost, half-matured compost and fully matured compost”

The fermentation process is divided in accordance with the level of maturity of the organic substances.
(1) Premature compost:
Easily decomposed organic substances are not yet decomposed in this stage. If the compost was applied asa fertilizer at this stage, diverse microorganisms in the soil may use the compost as a source of nutrients. As
a result, pathogenic filamentous fungi and other pathogenic bacteria could become prevalent in the soil.
Since easily decomposed organic substances are decomposed rapidly in the soil, plant roots might getdamaged due to gases and fermentation heat generated. If microorganisms grow rapidly in the soil, they
could take away nitrogen in the soil and cause nitrogen starvation. Experiences and techniques are required
if the premature compost was to be used, so the compost in this stage is not normally used.
(2) Half-matured compost:
Decomposition of organic substances that may be decomposed rapidly has completed, and relatively
easy-to-decompose organic substances still remain in this stage. The density of microorganisms in thecompost is high and they are active in the soil also. If the compost was applied as a fertilizer in this stage,
aggregation of soil is promoted and the soil improvement effect would be high. The compost in this stage issometimes used for this purpose. A point to keep in mind is that some time needs to be left as a break after
applying the compost as a fertilizer, before planting seeds, seedlings, etc.
(3) Fully matured compost:
Easily decomposed organic substances have been completely decomposed, but those difficult to decompose
still remain in this stage. The compost temperature has declined, and the temperature is not raised mucheven if cutback was performed. Mineralization of the fertilizing components has progressed, and activities
of microorganisms in the soil are mild. Although the soil improvement effect is lower compared to thehalf-matured compost, compost in this stage is relatively easy to handle.
Although the correlation among the “first stage, second stage, third stage,” the “premature compost,
half-matured compost, fully matured compost” and the “primary fermentation, secondary fermentation”
cannot be clearly indicated, the following diagram roughly illustrates the correlation.

12© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution

Fermentation temperature (°C)

Fermentation processes during composting
Cutback

Primary
fermentation

Secondaryfermentation

Time (weeks)
Fig. 5-8: Fermentation processes during composting
5.8.4

Judgment on the completion of composting

At which point of time could the compost be judged as having been completed?
In general, compost is regarded as desirable if “fully matured,” and many methods have been proposed forevaluating the compost quality from a viewpoint of maturity. On the other hand, judging from a viewpointof the needs of compost users, the fully matured compost is not always demanded. There are needs on
diverse types of compost products, such as premature compost that is almost raw, and half-matured
compost immediately after primary fermentation. As discussed in detail in the section for “soil preparation”
below, the author personally believes that half-matured compost is the most suitable. With half-matured
compost, microorganisms remain active while using organic substances remaining in the compost, evenafter the compost is applied as a fertilizer to the soil. As such, half-matured compost is the most efficient inbringing out the capacity to “improve the soil,” which is one of the effects of compost. In other words, byfinishing composting early in the state of half-matured compost, applying it as a fertilizer to the soil andletting it mature in the soil, the compost may be used effectively for soil improvement, which is madepossible by activities of microorganisms.
The author believes that an easy-to-understand guideline for discerning the time to take out thehalf-matured compost is at the time point when the compost temperature no longer exceeds 50℃ (the samewith the guideline for the time of completion of the primary fermentation).
There is a point of caution when observing the change in the temperature during composting.
The heat insulation effect of piled-up compost is high, and the temperature hardly declines even after theactivities of microorganisms slowed down and the amount of heat generation has reduced. In other words,“the temperature of compost is being maintained high” does not always mean that “microorganisms arehighly active and fermentation is underway vigorously.”13© 2019 Koji TakakuraChapter 5 Basic theories of composting technology – Matters requiring caution
An example is a case of compost made from piled-up waste that was cut back but not aerated. The compost
maintained high temperatures around 70℃ in the piled layers, even after elapse of one month after piling.
The high temperature was maintained not because fermentation is progressing, but simply because thedissipated heat was small.
Maintaining an unnecessarily high temperature is not always good for composting. It is also important toperform aeration and cutback appropriately for dissipating the heat.

References: Koji Takakura: Kaigai Gijutsu Kyoryoku wo Tsuujita Takakura-shiki Konposuto no Gijutsu Iten ni
Kansuru Kenkyu (A Study on Technical Transfer for Takakura Composting Method throughOverseas Technological Cooperation), doctoral thesis, Graduate School of Life Science and Systems
Engineering, Kyushu Institute of Technology, May 2016
 Editorial supervision by Shunrokuro Fujiwara, edited by Rural Culture Association Japan: Katei deTsukuru Namagomi Taihi (Home-made Raw Garbage Compost), Rural Culture Association of Japan,
1999
 Toshihide Matsuzaki: Tsuchi to Taihi to Yukibutsu (Soil, Compost and Organic Matters), Ie-no-Hikari
Association, 1992
 Deborah L. Martin and Grace Gershuny, editorial supervision by Shingo Iwata, translated by Midori
Sahara: Katei de Dekiru Taihi-zukuri Hyakka (The Book of Composting), Ie-no-Hikari Association,
2004
 Shinjiro Kanazawa: Konposuto Fujuku Katei ni Okeru Yukiubutsu no Henka Narabini Sono Hyoka(Changes in Organic Substances in Compost Maturing Process, and Evaluation Thereof), Suishitsu
Odaku Kenkyu (Journal of Researches on Water Pollution) Vol. 9, No.5, 1986
 Shunrokuro Fujiwara: Taihi no Tsukuri-kata, Tsukai-kata (How to Make and Use Compost), Rural
Culture Association of Japan, 2003
 Institute for Global Environmental Strategies: Composting for Waste Reduction; INFORMATION
KIT, 2010
 Minami-Boso City Government: III. Taihi no Seizo Hoho (III. Compost Production Method)
 Michinori Nishio: Dojo Biseibutsu no Kiso Chishiki (Basic Knowledge on Microorganisms in Soil),
Rural Culture Association of Japan Tetsuro Kato: Dojo/Hiryo no Kihon to Tsukurikata/Tsukaikata (The Fundamentals of Soil andFertilizers, and How to Make and Use Them), Natsumesha Co., Ltd.

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© 2019 Koji Takakura