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Composting Solid ManureReviewed: December 2008

Composting is a biological process that involves the aerobic decomposition of organic matter

to produce a humus-like product called compost. During the composting process, heat, variou

gases and water vapour are released, greatly reducing the volume and mass of the pile.

Benets of composting Drawbacks of composting

Destroys weed seeds and pathogens.•

Decreases bulk of raw inputs•

(estimated volume reduction of 50 - 70

per cent).

Finished compost has a consistent•

soil-like quality that makes it easier to

handle and apply.

Stabilizes nutrients as organic•

compounds.

Stable organic nutrients release more•

slowly, providing plants with a more

sustained source of nutrients for

growth.

Results in an odourless, potentially•

marketable product.

Emissions of ammonia, carbon dioxide,•

methane and nitrous oxide, especially in

the early stages.

Run-off from the compost piles must•

be controlled to prevent movement of

nutrients into ground or surface waters.

Aeration and moisture must be managed•

throughout the composting process.

Time, equipment and land are required.•

Some additional fertilizer may be needed•

to meet crop requirements.

The Composting Process



Table 1: Recommended conditions for rapid composting of solid manure*

Condition Reasonable

Range

Preferred Range

Carbon-to-nitrogen ratio (C:N) 20:1 - 40:1 25:1 - 30:1

Moisture content (%) 45-65 50-60

Oxygen concentrations (%) > 5 >5

Particle size (diameter - centimetres) 0.5 - 5.0 0.5 - 2.5

pH 5.5 - 8.0 5.5 - 8.0

Temperature ( º C) 43 - 66 54 - 60

*Source: On-Farm Composting Handbook, 1992

Composting is the aerobic (meaning it requires oxygen) decomposition of organic matter that begins with a diverse mixture

of organic material. During the composting process, micro-organisms convert raw organic materials into a stable, humus-like

product called compost. Finished compost generally varies from dark brown to black in colour, and has a pleasant, earthy odour.

The particles are relatively uniform and soil-like in texture. The proportion of humus (relatively stable, carbon-rich residue)

increases, and the C:N ratio decreases. The pH (a measure of acidity or alkalinity) is close to neutral and the cation exchange

capacity (measure of the nutrient-holding capacity) increases.

Composting generally results in a 50 to 70 per cent reduction in volume, and a weight loss in the order of 40 to 80 per cent.

Some of the shrinkage and weight loss is due to the transformation of loose, bulky material into nely textured compost and

the loss of CO2

and water to the atmosphere. During the process, nitrogen is lost to the atmosphere as ammonia (NH3). In

addition, the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N

2O) are emitted. Despite some losses

composting does retain most of the nutrients provided by the raw material, and stores them as stable organic compounds.

While this results in fewer nutrients being immediately available for crop growth, compost’s real agronomic value lies in thegradual release of nutrients that are slowly converted from stable organic compounds into available inorganic nutrients, and in its

properties as a soil amendment.

Animal Manures as Compost Material

Not all animal manures are created equal. Differences in animal type, age, diet, bedding and

management will all affect the characteristics of the manure. An appropriate C:N ratio and

moisture content are essential for successful composting. Most of the research literature

reports manure characteristics as excreted, without allowing for bedding, as there is a lot

of variability in the type and quantity of bedding. Producers should have their manure and

bedding mixtures analyzed prior to composting to ensure that the mixtures meet the criteria

for good composting. Assuming that bedding is present, cattle manure is a good composting

material, as it usually has sufcient carbon and moisture content. Odour is not usually

signicant if carbon is sufcient and the pile is managed properly.

Poultry manure usually has a higher nitrogen content than other animal manures, and is

moderately moist. Low C:N ratios may be an issue, so it is important to have a laboratory

check these ratios. If carbon must be added, chopped straw, sawdust and wood shavings

are good sources. Nitrogen loss and odour associated with ammonia are sometimes

problems when composting poultry manure, due to the high nitrogen content and high

pH. Amendments may be needed to lower the pH. On the other hand, poultry manure

decomposes quickly, and the high nitrogen content can result in excellent compost with

high nutrient value. Swine manure from solid-based systems usually contains straw and is

nitrogen-rich and relatively moist. Insufcient bedding and a low C:N ratio will result in odour,

so it is important to ensure that the mixture meets the criteria for good composting.

Horse manure is also a good composting material, and tends to be relatively dry with a high

C:N ratio due to the amount of bedding. It will compost well and could be added to a wetter

manure, like cattle manure, if needed.

Composting Challenges

Time and Recipe

Composting is a biological process that takes time. How much time will depend on a number of factors, including the C:N ratio,

moisture content, weather, type of operation, management and the types of waste being composted. The unprocessed manure

consists of livestock waste (feces and urine), bedding material, water and feed waste. The C:N ratio of manure depends largely

on the amount and type of bedding material in the manure. Straw and wood shavings are usually rich in carbon and low in

nitrogen, compared to urine and feces. Producers should have the manure and bedding analyzed for C:N ratio, density and

moisture content. Preferred ranges are summarized in Table 1. In the event that the C:N ratio needs to be adjusted, a recipe

(proportion of raw materials) can be calculated with the help of a composting manual.

In general in the prairie climate, well-managed windrows or static piles take an average of four months to compost. More

Cattle manure makes good compos

Straw being added to a pig barn



sophisticated in-vessel systems (closed or open) may take as little as one to four weeks to complete the composting operation.

With these systems, there is usually a one- to two-month curing period that follows. Factors that slow composting include a

lack of moisture, high C:N ratio, low temperatures, insufcient aeration, large particles and too many components that are too

resistant to decomposition.

The ultimate end-use of the compost will also determine the length of the composting process. If, for instance, the compost is

going to be land-applied, it can be effectively nished and cured in the eld following application. If the compost needs to be

very dry or stable to suit a particular market, the composting period may have to be increased.

Temperature

Temperature is an indicator of the level of microbial activity in the compost, and should be

monitored daily, if possible. Temperature probes can be purchased, and should be long enough

to penetrate one-third of the way to the centre of the pile. The compost pile starts out at ambient

air temperature, but, as micro-organisms start to multiply, the temperature of the pile rises rapidly.

The composting process is divided into three phases: psychrophillic, where temperatures are less

than 10ºC; mesophillic, where temperatures are between 10ºC and 40ºC; and thermophillic, where

temperatures exceed 60ºC.

Compost should be turned if the temperature in the pile drops below 30ºC, which indicates that

there is little microbial activity, or if the temperature rises above 60ºC, which may result in the death

of composting bacteria. A sustained temperature of 55ºC for 14 days will result in the destruction

of most pathogens and weed seeds (laboratory conrmation is recommended). However, failure to

achieve sustained high temperatures can result in y and odour problems. Compost temperatures

will generally decline if moisture or oxygen is insufcient or if the carbon source is exhausted. Someaverage frequencies for turning are given in Table 2, but the best approach is to monitor the piles

frequently to determine activity.

Table 2: Typical Composting Times

Method Composting Time Turnings Curing Time

Windrow Typically four months Turn if: 1) the temperature rises above

60ºC or 2) the temperature drops to near

30ºC. Rule of thumb: Once per week for

the rst month, once every two weeks for

the next three months, once a month for

the fourth and fth months, then let cure.

One to three months.

Pile is ready to cure when the

temperature remains at a constant

ambient temperature, even after

turning.

Aerated Static pile Typically four weeks Not usually applicable One to two months

In-vessel seven to 30 days Varies with type of vessel and turning

unit. Continuous automated turners are

common with this system.

One to two months

Moisture

Moisture is essential to nourish the composting bacteria. Mixtures that are too dry will stop the composting process. Piles that

are too dense and wet can quickly become smelly and y-ridden. Experience has shown that the composting process slows

when the moisture content drops below 40 per cent. Moisture levels above 65 per cent result in water displacing much of the

air in the pore spaces in the compost pile. This condition limits air movement and results in an anaerobic (lacking oxygen) pile.

Maintaining adequate moisture in the preferred 50 to 60 per cent moisture range can be a challenge. The high temperatures

associated with the mesophillic stage of composting often result in signicant moisture loss, and it may be necessary to add

water to the piles in order to maintain adequate moisture. Alternatively, piles that are too wet may require the addition of a dry

amendment like straw or wood shavings.

Moisture levels can also change throughout the composting process as water is added in the form of rain or snow, or evaporates

from the pile. Generally, the moisture content of the pile decreases during composting, since more water evaporates from the

pile than is added. The pile should be kept thoroughly damp without being waterlogged.

A hand test is perhaps the simplest method of determining moisture. The material is too wet if water can be squeezed out of

a handful, and too dry if the material does not feel moist to the touch. Ideally, a handful of the material should be able to be

squeezed into a ball that will stick together yet break apart easily. Note: If using this method, the compost should be removed

from the pile mechanically, or with a shovel, as the compost pile can be extremely hot. Moisture probes are also available.

Oxygen and Aeration

Composting is an aerobic process, meaning it requires air (a minimum of ve per cent oxygen is necessary). When oxygen falls

This pile is at an optimum

temperature of 146ºF (63ºC)



below this level, the pile will become anaerobic. Anaerobic processes

use different bacteria, are slower than aerobic processes and

produce compounds that will cause odours. Odour is a good indicator

that it is time to turn or aerate a compost pile. Turning or remixing the

pile will add oxygen. In more sophisticated systems, such as aerated

static piles or concrete in-vessel systems, air is forced or sucked

through the compost mixture by a blower.

Particle Size, Porosity, Structure and Texture

Particle size, shape and consistency will affect the compostingprocess by inuencing aeration. Essentially, composting will proceed

more quickly if you have larger, relatively uniform particles to ensure

that there are air spaces throughout the pile. Usually, mixtures of

manure and straw are sufciently bulky to compost successfully. In

some cases where the compost materials are very dense, a bulking agent or amendment might be required to ensure that there

is enough oxygen for proper composting. Depending on the type of bulking agent, it may have to be mixed or ground to the

appropriate size before being added to the compost pile.

The structure of the compost pile is important: good structure prevents the loss of porosity (air space) in the pile. As the amount

of surface area increases with the decrease in particle size, the rate of aerobic digestion also increases and decomposition

proceeds more quickly. However, if particles are too small or lack structure, the process can be slowed. Particle sizes of

between 0.5 to 5.0 centimetres are usually adequate for good composting. A pile that heats successfully continues to compost

after turning, and is not overly smelly. This is usually indicative of adequate food and oxygen for microbial activity.

Curing

In addition to the time required for composting, the amount of time required for curing and storage must also be considered.

The pile is ready for curing when turning no longer results in an increase in temperature. Curing is the “cool” part of the process,

where fungi digest the carbons not degraded during composting and further stabilize the nutrients. This process takes time

(one to two months), so the piles should not be disturbed during that period. Compost is considered “nished” based on a

number of characteristics that are related to its use and handling. These characteristics are summarized in Table 7. Once

cured, the compost can be screened, if necessary, to remove any non-degradable compounds, and should then be analyzed to

determine nutrient value. The compost may need to be stored for a period of time, so storage space should be considered when

calculating the amount of land required for a composting site.

Composting Methods

Manure is generally composted in machine-turned windrows, in aerated windrows (called static piles) or in in-vessel systems.

The nished compost is usually cured outdoors in windrows. Regardless of the process, composting requires space. Some of

the more common methods for composting are:

Machine-Turned Windrow: This method involves the arrangement of the compost mixture in long, narrow piles or windrows

that are periodically turned to maintain aerobic conditions. The size and shape of the windrow will depend on the type of

machinery used for turning and on the characteristics of the pile. Typically, manure windrows are one to two metres high, three

to six metres wide. In winter, larger piles will tend to lose less heat, as they are better insulated.

Aerated Windrow or Static Piles: Aeration can be either passive or active. In passively aerated static piles, the material is

usually aerated by a system of perforated pipes placed in the windrow. In actively aerated windrows, the material is stacked on

perforated plastic pipe or tubing through which air is drawn. Actively aerated windrows will compost more quickly. Although no

turning of the material is required in either system, occasional turning is still recommended to redistribute moisture and exposefresh material to microbial activity.

In-vessel: This process involves conning materials in a building (often long concrete channels), container or closed vessel.

There is a variety of in-vessel composting methods, most of which rely on forced air and mechanical turning. Although fast, this

method can be quite costly, but when a high quality of compost is required for a particular market, the automated system allows

for the greatest control over the composting process.

A hay moisture probe with a long stem works well to

measure the relative moisture of a compost pile. This pile

is at the correct moisture level of about 45 per cent.



Selecting a Composting Method

Selecting a composting method involves determining what method will t best with your particular operation and needs.

Consideration must be given to the level of management that can be applied, the availability of equipment and labour, the space

requirements for the material and access, the quality of the compost required, and potential issues due to climate and the cost.

Table 3: Advantages and Disadvantages of Three Composting Methods

Method Advantages Disadvantages

Windrow Able to handle large volumes.

Low capital investment.Rapid drying with high temperatures.

High degree of pathogen and weed seed kill.

Drier product, resulting in easier handling of material.

Good product stabilization.

Not space-efcient.

Equipment (varies greatly in price) and labour isrequired for turning and monitoring.

Vulnerable to climate changes (rain, snow, drought).

Odours released with turning.

Bulking agents might be required.

Aerated

Windrow or

Static Pile

Able to handle large volumes. Low capital costs.

Relatively space-efcient.


Good odour control.

Good product stabilization.

Not space-efcient.

Operation and maintenance costs for blowers and

fans.

Loading and unloading equipment required.

Placement of aeration system may present

operational difculties.

Vulnerable to climate changes (rain, snow, drought,

cold).

In-Vessel Space-efcient.

Good control of composting process with connement

and automation.

Predictable, uniform product.


Potentially good odour control.

Protection from climate.

Potentially not visible.

Can be designed as a continuous process rather than a

batch process.

High capital cost for sophisticated units with

automated turners, forced air and monitoring systems

Careful management required.

Less exibility in operation than with other methods.

Specialized windrow turner In-Vessel Composting

Windrow method of composting Side arm windrow turner





Table 5: A truckload of manure versus a truckload of compost (Truck volume = 12 m3)

Fresh Manure Compost

Wet Bulk Density 500 kg/m3 650 kg/m3

Load weight 6 tonne 7.8 tonne

Wet weight 6000 kg 7800 kg

Dry matter weight 2400 kg 4860 kg

*Nitrogen 40 kg/truckload 80 kg/truckload

*Phosphorus 8 kg/truckload 24 kg/truckload

Site Selection

Good site selection is very important for the success of a composting site. Producers will need to consider soil type, topography,

location of water sources, access for handling and hauling, distance from neighbours, wind direction and aesthetics. Some sites

may be suitable for composting with only minimal development, whereas other sites may require more engineering. Operators

of facilities that require year-round pen cleaning and stockpiling have to ensure that the stockpile is contained or covered, if

necessary.

To minimize handling, the composting facility should be located close to the manure source. Even well-managed compost sites

generate odour, at least initially, so wind direction and proximity to neighbours should be considered when locating the compost

site. Topography is also important. Avoid locating compost sites on slopes where run-off may be a problem or in depressions

where the compost may become saturated with run-off. Generally speaking, the composting and curing sites should be located

on clay or till subsurface soils. The compost site should be slightly sloped to allow drainage. Run-off should remain on the

property naturally or retention berms can be constructed. In areas with high rainfall, composting facilities may need to be coveredin order to prevent excessive run-off or leaching. Proper siting and design will minimize any impact from runoff or leachate on

ground and surface waters. Producers should contact the appropriate government ministry to determine the requirements for

developing a compost site as part of a manure management plan.

The type of composting method chosen will inuence the amount of space required. The windrow method requires the most

land; aerated windrows or static piles would follow, with in-vessel systems requiring the least amount of space. The pile

dimensions will also affect the land requirement. Large piles with low surface-area-to-volume ratios require less land but are

more difcult to manage, and will potentially require larger and more specialized equipment. Allow space for stockpiles, berms,

runoff containment structures, curing and storage. Curing areas will generally require half as much space as composting

areas. Storage requirements will depend on the length of time that the compost will remain at the site. When designing the site,

remember to leave enough room to operate equipment in and around the piles. Allow for additional space if a buffer is desired fo

trees or some other visual barrier.

Determining the Required Area and Layout of the Composting Pad

Composting Pad: The area required for the composting pad depends

on the volume of material handled, pile/windrow shape and length, and

the space needed to maneuver equipment.

Curing and Storage: The space requirement for curing and storage is

based upon the amount of organic material composted, the pile height

and spacing, and the length of time the compost is cured and stored.

The volume of compost produced is generally about half the original

material being composted. When calculating the area required for

curing, allow for the movement and loading of vehicles.

How much space do you need for composting and curing?

Table 6 gives some estimates of the area required for composting and

curing manure from various animal species. The estimates assume thefollowing:

windrows are six ft. (1.8 m) high and 12 ft. (3.7 m) wide;•

windrows are grouped in pairs side by side with two ft. (0.6 m) between them;•

pairs of windrows are spaced 20 ft. (six m) apart;•

10 ft. (three m) is allowed to maneuver around the piles;•

the curing area occupies ¼ of the space of the composting area; and•

a front-end loader turns and moves the compost.•



Table 6: Estimated area for composting and curing

Species Number Area (acres) Area (metres) Manure Production (months) Manure Volume (L or ft3/day/animal)

Cow / calf 100 ¾ 55 x 55 6 63 litres or 2.22 ft3

Feeder cattle 1 000 3 110 x 110 8 25 litres or 0.9 ft3

Broilers 100 000 ½ 45 x 45 4 0.07 litres or 0.0024 ft3

Feeder hogs 1 000 1¼ 70 x 70 4 18 litres or 0.63 ft3 The diagram below illustrates this scenario for a 100-head cow/calf operation.

Typical layout for Windrow Composting

These tables and diagram are examples. The actual area required will depend on the volume of manure, frequency of clean-out

frequency of aeration, height and width of windrows, spacing of windrows, type of equipment, height of the curing pile and lay-

out of composting and curing areas.

Composting Regulations

In Canada, three organizations are responsible for the development of regulations, guidelines and standards for compost: the

Canadian Food Inspection Agency (CFIA), the provincial and territorial governments and the Standards Council of Canada

(SCC). The CFIA regulates compost under the authority of the Fertilizers Act and Regulations. All compost that is sold in or

imported to Canada must comply with the requirements of the Act, which includes provisions for product safety, benet claims

and labeling. The provinces and territories are responsible for regulating the disposal and use of waste, including compost. In

Saskatchewan, municipal composting would come under the water management jurisdiction of Saskatchewan Environment

(SE). If a municipal waste management facility were using manure as one of the compost components, this would be identied

in the permit application to SE. There is no requirement for a permit through SE for on-farm composting of manure. However,

Saskatchewan Agriculture requires Manure Storage and Manure Management Plans for intensive livestock operations. If

composting is to be part of this plan, then an approval may be required under The Agricultural Operations Act.

Compost Quality

Compost quality can be determined through laboratory tests. Good compost is characterized by a low moisture content, black to

dark brown colour, earthy odour, high tilth (due to texture and particle size), and consistent and stable nutrient concentrations.

Age, storage conditions and raw materials will also affect the nal quality of the product.

Agriculture and Agri-Food Canada, the provincial and territorial governments with the assistance of the Canadian Council

of Ministers of the Environment (CCME) and the Bureau de Normalization du Quebec on behalf of the Standards Council of

Canada-have developed a set of compost quality standards. The standards are based on four criteria: product safety and

quality, maturity, foreign matter, and trace elements and pathogens. There is little variation between standards, and they all

adhere to the same standard for product safety. Saskatchewan follows the CCME guidelines as outlined in Table 7.



Table 7: Classication of Compost.

Compost Quality Criteria Category A Compost Category B Compost

Restrictions to compost application. Can be used for all types of applications:

agricultural land, residential gardens,

nurseries, and horticulture operations.

Restricted use: may be controlled under

the provincial or territorial regulations.

Trace Elements

mg/kg (ppm) air dried mass

(Maximum allowable concentrations)

Arsenic, As 13

Cadmium, Cd 3

Cobalt, Co 34

Chromium, Cr 210

Copper, Cu 100

Mercury, Hg 0.8Molybdenum, Mo 5

Nickel, Ni 62

Lead, Pb 150

Selenium, Se 2

Zinc, Zn 500

Arsenic, As 75

Cadmium, Cd 20

Cobalt, Co 150

Chromium, Cr not stated

Copper, Cu not stated

Mercury, Hg 5Molybdenum, Mo 20

Nickel, Ni 180

Lead, Pb 500

Selenium, Se 14

Zinc, Zn 1850

Category A and B Compost

Maturity Compost is deemed mature if it meets two of the following:

the C:N ratio is 25:1

oxygen uptake rate is 150 mg O2/kg volatile solids/hr

germination of cress and radish seeds is > 90% of germination rate of control sample.

The manure must be cured for 21 days, and must not reheat upon standing to >20° C

above ambient temperature.

Foreign Matter Compost must not contain any sharp foreign matter >3mm in any dimension that maycause damage or injury to humans, animals and plants during or resulting from its use.

Pathogens The quantity of fecal coliforms must be <1000 MPN/g (Most Probable Number per gram)

of total solids on a dry weight basis.

No salmonellae present (<3 MPN/4 g total solids).

Marketing Your Compost

In order to sell compost, either bagged or in bulk, The Fertilizers Act and Regulations require that several things be done:

The compost should be analyzed, by batch, for nutrient content, organic matter content, etc. The compost can then be•

packaged and labelled according to product claims.

The compost must be classied based on product quality, safety and aesthetics. The• Regulations and Guidelines of

Impact to the Marketing of Compost in Ontario is a helpful resource, with a complete description of the standards for each

classication of compost.

The compost must then be classied under • The Fertilizers Act as a fertilizer (contains nitrogen, phosphorus, potassium

or other plant foods) or a supplement (not a fertilizer but sold for the purpose of soil improvement). While compost does

not have to be registered under the Act, it still must conform to the Act’s requirements and standards for fertilizers or

supplements. Names and standards of fertilizers and supplements can be found in Fertilizers Act, Schedule II.

The compost must be labelled (directly on the bag or on a separate document with a bulk shipment) in accordance with•

the claims made for the product. The label for a compost with no nutrient claims must include the brand, name, net weight

lot number (if applicable), expiry date, directions for use, guaranteed analysis, the minimum amount of organic matter,

maximum amount of moisture, any cautionary statements and the name and address of the registrant or responsible

packager. The label for compost with nutrients must also contain the grade of the compost as well as the percentage of

nutrients.

For more detailed information on composting, consult a composting handbook and record-keeping guide such as the On FarmComposting Handbook, available from Olds College, 4500 - 50th Street, Olds, Alberta, Canada. T4H 1R6. For more information,

call Saskatchewan Agriculture , Inspection and regulatory Management Branch, at 306-787-4680.

Resources

Composting Council of Canada . 1999. Setting the Standard: A Summary of Compost Standards in Canada . Located at www.

compost.org/standard.html

Canadian Organic Growers Inc. 1992. Manure Management and Composting : COG Organic Field Crop Handbook . Ecological

Agriculture Projects , McGill University (Macdonald Campus), Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada. Located at http://

eap.mcgill.ca/MagRack/COG/COGHandbook/COGHandbook_1_4.htm

Fonstad, T.A, Leonard, Dr. J. 2001. Evaluation and Demonstration of Deads Composting as an Option for Dead Animal

Management in Saskatchewan . Department of Agricultural and Bioresource Engineering, University of Saskatchewan ,

Saskatoon , Canada .

Larney, F.J., Freeze, B.S., Olson, A.F. and Heigh, J.T. 1999. “Transporting nutrients in manure and compost.” Abstract in



Growing with Compost Conference, Olds College , Olds, AB. April 7-9, 1999 .

Larney, F.J., Yanke, L. Jay, Miller, James J. and McAllister, Tim A. “ Fate of Coliform Bacteria in Composted Beef Cattle Feedlot

Manure” in Journal of Environmental Quality: 32:1508-1515 (2003).

Krider, James N. (editor). 1992. Agricultural Waste Management Field Handbook . U.S. Soil Conservation Service. Washington ,

D.C.

Paul, Dr. J. 1996. Composting Agricultural Waste. Proceedings Manure Management Symposium, Winnipeg , Manitoba .

Rynk, R.(editor). 1992. On-Farm Composting Handbook . NRAS-54. Northeast Regional Agricultural Engineering Service. 152

Riley-Robb Hall, Cooperative Extension, Ithaca , NY . 14853-5701

Saskatchewan Agriculture and Food. 1997. Guidelines for Establishing and Managing Livestock Operations.

Tompkins, D. K., Chaw, D., and Abiola, A.T. 1998. “ Effect of windrow composting on weed seed germination and viability” in

Compost Science and Utilization, Winter, Vol. 6, No. 1, pp 30-34.

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