Introduction
Composting is the aerobic (oxygen requiring) decomposition of manure or other organic
materials in the thermophilic temperature range of 104 – 149° F (40 - 65° C). Nature provides an
extensive, native population of microorganisms that are generally attached to all organic wastes.
When conditions are right, these microbes grow and multiply by decomposing the material to
which they are attached. From a scientific viewpoint, the composting process is started and
managed under controlled environmental conditions rather than accepting the results of natural,
uncontrolled decomposition. The composted material is odourless, fine-textured, and low-moisture
and can be used for non-agricultural and agricultural purposes with little odour or fly
breeding potential. When managed properly, composting improves the handling characteristics
of any organic residue by reducing its moisture content, volume and weight. The process
increases the value of raw manures by destroying pathogens and weed seeds and creating a
media for the production and proliferation of beneficial organisms.


The Composting Process
The composting process is a biological one that compares somewhat to the raising of plants or
animals. The rate of composting, like the rate of plant or animal growth, can be affected by a
number of factors.
Four keys factors are:

1. nutrient balance
2. moisture content
3. temperature
4. aeration

Nutrient balance is determined primarily by the ratio of carbon to nitrogen in the compost
mixture. The microorganisms require carbon and nitrogen for growth since these elements are
the main components of carbohydrates and protein. If nitrogen is in excess, large amounts of
ammonia will be released to the atmosphere, if carbon is in excess the composting rate will
decrease. The moisture content should ideally be 60 percent after organic wastes have been
mixed. Maintaining the correct moisture level during the thermophilic (high temperature) phase
of composting can be difficult in an open-air windrow system due to dry or wet climatic
conditions. When the moisture content exceeds 60 %, the windrows subside and lose porosity
thereby becoming anaerobic. Fermentation will set in and odours will be emitted from the
material. If the moisture content decreases below 50 %, the rate of decomposition decreases
because nutrients must be in solution to be utilized by microorganisms. As the microorganisms
decompose organic matter, heat is generated and the temperature of the compost rises.
Decomposition is a dynamic process, accomplished by a succession of microorganisms, each
group reaching its peak population when conditions are optimum to support that particular group.

When one group of microorganisms dies, another group populates the composting material until the next incremental change in nutrition and temperature occurs. Since the release of heat is directly related to the microbial activity, temperature is a good process indicator. The temperatures of composting materials typically follow a pattern of a rapid increase to 120 – 140° F (49 - 60° C) which is maintained for several weeks, a gradual temperature decrease to 100° F (38° C) as active composting slows due to nutrient consumption, and a final leveling off at ambient air temperature. The temperature pattern is generally described in Figure 1. During the

Figure 1. General time-temperature pattern for composting.

initial days of composting, readily degradable components of the raw material are rapidly
metabolized, therefore the need for oxygen is greatest at the early stages and decreases as the
process continues. Without sufficient oxygen, the materials become anaerobic. Anaerobic
processes are generally slower and less efficient than aerobic processes. Little heat is generated
under anaerobic conditions and intermediate compounds such as methane, organic acids,
hydrogen sulfide and other odourous compounds are generated. Aeration also removes heat,
water vapour and other gases trapped within the composting materials. Livestock manures will
compost rapidly under the conditions listed in Table 1.


Table 1. Recommended conditions for rapid composting ^a .

Condition	Reasonable Range	Preferred Range
Carbon/Nitrogen ratio	20:1 – 40:1	25:1 – 30:1
Water content	40 – 65 %	50 – 60 %
Oxygen concentration	5 %	5-15 %
Particle size (diameter)	1/8 – 1/2 inch	varies b
pH	5.5 – 9.0	6.5 – 8.0
Temperature	110 – 150° F(43 – 65° C)	130 – 140° F (54 – 60° C)

^a from Rynk et al. 1992
^b depends on materials used

Composting Alternatives
Open-windrow composting using some form of mechanized turner is frequently the method of
choice for intensive beef production operations (Figure 2a). Other methods commonly used for
composting include: passive composting piles (also referred to as static pile composting),
passively aerated windrow (supplying air at ambient pressure through perforated pipes embedded
in the windrow), active aerated windrow (forced air through perforated pipes [Figure 2b]), turned
bins, rectangular agitated beds, silos, rotating drums, and vermi-composting (using worms to
degrade organic material). Front end loaders, skid steers with buckets, conventional solid
manure spreaders, tub grinders or mixing wagons are among the equipment used to mix the
compost ingredients and deposit the material in windrows. The method selected depends on the
type of livestock, size of the operation, climatic conditions and available capital. Fabric covers
have recently been made commercially available to cover open-air windrows, protecting the
material from changing climatic conditions, yet allowing free gas-exchange. Static pile
composting is generally not recommended where a rapid composting strategy is required (eg.
where composting space is limited). Front end loaders, skid steers with buckets, conventional
solid manure spreaders, tub grinders or mixing wagons are among the equipment used to mix the
compost ingredients and deposit the material in windrows.

Figure 2a. Open windrows with mechanical turning.
From Rynk, R. et al. 1992.



Figure 2b. Active aerated windrow. From Rynk, R.
et al. 1992.

Turning the windrows restores porosity to the piles and reduces the particle size increasing the
surface area of bulking material like straw. During the turning process oxygen is introduced into
the windrow but it normally is rapidly consumed by microorganisms often within a matter of
hours. However, restoring porosity enhances the passive movement of air into the windrow and
accelerates decomposition. Excessive turning of the material can accelerate nitrogen loss, water
loss and result in cooling of the compost. Generally turning the compost once a week for the
first 4 weeks (with initial moisture levels of 70%) then once every 2 weeks for the next 8 weeks,
under the normal moisture conditions found in Manitoba, has been found to yield an excellent
composted product without the addition of water. It is critical to maintain the moisture level in
the range of 60% in the initial 4 weeks of composting. If the moisture levels falls below 50%
composting activity will slow and eventually cease as the material continues to dry.


Nutrient Content of Compost Ingredients
Manure nutrient contents vary according to species, diet, and handling systems for animal
wastes. The bulking agent used as a source of carbon or amendment to increase porosity of the
mixture varies according to preference and availability. Chemical characteristics of livestock
manure and common bulking agents are given in Table 2 and 3. Depending on the bulking

Table 2. Range of manure characteristics from several livestock species ^a .

Characteristics	N	P	Water Content	C:N	pH
	----------------------------%--------------------------
Beef feedlot b	0.2 – 3.0	0.1 – 1.2	20 – 80	10:1 – 20:1	6 – 8
Swine	0.1 – 0.5	0.1 – 0.2	80 – 99	15:1 – 21:1	7 – 8
Dairy	0.3 – 0.6	0.1 – 0.2	75 – 90	8:1 – 30:1	6 – 8
Chicken manure	0.8 – 2.5	0.3 – 0.7	50 – 85	4:1 – 18:1	6.2 – 7.5
Broiler litter b	1.7 – 6.8	0.8 – 2.6	22 – 29	6:1 – 24:1	6.5 – 8.5
Turkey	1.2 – 1.8	0.3 – 0.9	50 - 85	4:1 – 18:1	6.2 – 7.5

^a from Eghball and Zhang 1998.
^b beef feedlot manure and broiler litter as collected, others on a fresh manure basis.

agent used in the mixture solid manure or separated liquid manures can be composted in 60 –
120 days using windrow composting and mechanical turning. Chicken manure, broiler litter and
turkey manure mixtures frequently require the addition of water to achieve the desired moisture
content. Temperatures in these composts have been known to exceed the maximum
recommended temperature levels and require close monitoring to produce a quality product.
High carbon amendments are known to reduce nitrogen loss from high nitrogen manures
(Mahimairaja et al 1994, Eghball et al 1997).

Table 3. Carbon content and C:N ratios of common bedding materials ^a

Material	% N (dry wt.)	C:N
Straw	0.3 – 1.1	48 – 150
Newsprint	0.06 – 0.14	398 – 852
Sawdust	0.06 – 0.8	200 – 750
Wood chips	0.04 – 0.23	212 – 1313

^a adapted from Rynk et al. 1992

In spite of the variability in nutrient content of manures and cereal straw, as well as the
variability in proportion of each of these ingredients in the mixture, in most cases the material
composts extremely well and the addition of inoculum to speed the process is of questionable
value.


Compost Quality
The three factors described by Jim Wimberly (Director of the Foundation for Organic Resource
Management, Fayetteville, FL) that define compost quality are consistency, absence of
pathogens and fine texture. The nitrogen, phosphorus and potassium in the composted manures
are not the components of highest value. The greatest benefit is probably in the
microbiology and the organic matter of the material. Currently there is no value attached to
these components and, until this value is established through research, the margin of return for
composted manure products will remain low. According to Bess (1999), microbiological
methods used to evaluate soil microbiology may be used in the future as standard analytical
methods to determine compost quality. Compost quality could be determined, in part, by the
concentration of six functional groups of microorganisms: aerobic bacteria, anaerobic bacteria,
fungi, actinomycetes, pseudomonads and nitrogen-fixing bacteria. There is evidence that
specific organisms that inhibit the growth of plant pathogens can be isolated from compost and
compost extracts. It has been suggested that composts could be tailored to suppress specific
plant diseases prevalent in horticultural and agricultural production (De Ceuster and Hoitink
1999 ) and to clean-up environmental contamination (Alexander 1999). Another indicator of
compost quality is compost maturity, which is determined by an assay for the presence of
phytotoxic compounds, and measurement of pH, sodium content and electrical conductivity.


Composting
Summary of Pros and Cons

Benefits

• production of an excellent soil conditioner that adds organic matter, improves soil structure,
  improves water-holding capacity, reduces fertilizer requirements and reduces potential of soil
  erosion.
  
• potential market for the composted product ie. home gardeners, landscapers, vegetable
  farmers, turf growers, golf courses and ornamental growers. Compost can also be used as
  bedding for poultry.
  
• reduction in weight and mass, and improvement in handling characteristics.
  
• product can be stored and applied at convenient times of the year since organic N is less
  susceptible to leaching and further ammonia losses
  
• reduction of the C/N ratio to levels than are more suitable for land application compared to
  raw manure mixed with straw.
  
• destruction of pathogens and weed seeds.
  
• elimination of odours and flies.
  
• reduction of soilborne pathogens without the use of chemical controls
  
• potential income from tipping fees for organic waste. Note: composting off-farm wastes
  must be considered cautiously.

Disadvantages

• a suitable site must be developed for composting activities to prevent runoff and leaching of
  nutrients. The composting site, storage of raw materials and finished compost can occupy a
  considerable area of land.
  
• cost of equipment, labour and management.
  
• potential odours from stockpiled materials collected for composting.
  
• climatic limitations may require a higher capital investment.
• development of a marketing plan for excess compost.
  
• diversion of nutrients from agricultural land to other uses.
  
• potential loss of nitrogen (however, the total losses from raw manure compared to
  composting have not been determined scientifically).
  
• slow release of nutrients due to the higher concentrations of organic nitrogen in compost
  compared to manure (this could be considered a benefit on soils with poor nutrient retention
  capacity).

References
Rynk, R. et al. 1992. On-Farm Composting Handbook. NRAES. Ithaca, NY.
Eghball, B. and Zhang, R. 1998. Composting manure and other organic residues in the North
Central Region. North Central Regional Extension Publication No. 600. Lincoln, NE.
Mahimairaja, S., Bolan, N.S., Hedley, M.J. and Macgregor, A.N. 1994. Losses and
transformation of nitrogen during composting of poultry manure with different amendments:
an incubation experiment. Bioresource Technology 47:265-273.
Eghball, B. et al. 1997. Nutrient, carbon, and mass loss during composting of beef cattle feedlot
manure. Journal of Environmental Quality 26:189-193.
Bess, V. 1999. Evaluating microbiology of compost. Biocycle May, pg.62.
De Ceuster, T.J.J. and Hoitink, H.A.J. 1999. Using compost to control plant diseases. Biocycle
June, pg. 61.
Alexander, R. 1999. Compost markets grow with environmental applications. Biocycle March,
pg. 43.

Katherine E. Buckley
Agriculture & Agri-Food Canada
Brandon Research Centre, Brandon, MB R7A 5Y3