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handsful of compost
Although manure can decompose on its own, composting is a method of speeding up this natural process. The breakdown of manure and bedding occurs much more rapidly in the compost pile because the environment can be made ideal for the microbes to do their work. The end result of composting is a dark, crumbly, earthy-smelling product similar to potting soil. Composting is of particular interest to horse owners because, if it is done properly, composting kills parasites eggs and larvae and destroys weed seeds in horse waste. So, when the compost is later spread on pastures, the possibility of re-infection is greatly reduced. Composting also reduces the odor of the manure and can decrease the size or volume of the pile by 50 per cent. Finished compost can be used to improve soil quality and nurture your pastures, or sold to serve as a mulch or growing media for plant nurseries, gardeners, mushroom growers and worm farms.

Understanding the Process

Composting is a natural process in which organic material decomposes.  The process starts as soon as the organic materials are mixed together. There are various micro-organisms which are naturally present in all organic matter, and it is important to understand the difference between the "aerobic micro-organisms" needed for good composting, and the "anaerobic micro-organisms" that flourish in oxygen-deprived conditions, that produce unpleasant ordors. start work on the easily degradable compounds such as sugars, organic acids and amino acids.  During the process, the microbes consume oxygen while feeding on the organic matter and produce heat, carbon-dioxide (CO2) and water vapour.  This is referred to as the "active phase" of composting. If the heat is not adequately dissipated, temperatures will continue to rise, killing off most micro-organisms, an undesirable outcome. Turning and mixing the pile is required to dissipate the heat, and encourage the breakdown of the material into smaller particles.It is clear then that these aerobic micro-organisms are essential to the composting process, and by providing optimum conditions the composting process can be completed in the shortest possible time.

Recipe for Successful Composting

Components of this "recipe" for successful composting include a number of key ingredients:

Porosity of material - This is the ratio of the volume of space between solid particles, to the total volume of particles plus space.  This is important because sufficient space must be available to hold the oxygen required for microbial action.  Turning and mixing the pile improves porosity and mixes oxygen into the pile.

Moisture content - Moisture plays an essential role in the matabolism of micro-organisms, and indirectly in the supply of oxygen. Microbes can utilize only those organic molecules that are dissolved in water. Moisture levels between 50-60% provide adequate moisture without limited aeration.  If the moisture content falls below 40%, bacterial activity will slow, ceasing altogether below 15%. When the moisture content exceeds 60%, nutrients are leached, porosity  is reduced, decomposition slows and odours are produced to the anaerobic conditions.  The squeeze test can be used: too wet if water can be squeezed out of a handful, and too dry if the material does not form a ball when squeezed.  If the pile (or windrow) becomes too wet, it should be turned which allows air to circuclate back into the material, and improves porosity for better draining and drying.  If the material is too dry, water can be added.  The Frontier Mighty Mike has an optional watering tank so that water can be added while the windrow is being turned.

Oxygen concentration - Microorganisms need air (oxygen) to be able to decompose manure properly. To provide space for air to move in and out of the pile, manure should be combined with bulkier materials, such as wood shavings or straw bedding mucked from a stall, or even lawn clippings, leaves or hay. Without sufficient oxygen, the process will become anaerobic and produce undesirable odors. Earth's atmosphere is 21% oxygen.  Aerobic microbes can survive at concentrations as low as 5%.  Oxygen concentrations greater than 10% are considered optimal for maintaining aerobic composting.  Optimum conditions are maintained by mixing and turning the compost ingredients.

Temperature - As microorganisms decompose manure and bedding, their body heat causes the temperature in the pile to rise. Greater heat is necessary to kill weed seeds and parasites. Effective composting takes place around temperatures of 55 to 65°C. Temperatures can soon exceed 70°C (158°F), but then many organisms begin to die, which stops the active composting phase. The temperature can be measured with a 3 ft.long dial temperature probe.

Pile size: The size of the pile influences whether the pile will hold heat. Small piles are usually colder and dry out faster. A pile of at least one cubic meter (3.5 x 3.5 x 3.5 feet) is big enough for year-round composting, even in the winter cold.

Nutrients: Microbes use carbon, nitrogen and other nutrients from materials added to the pile to support their own growth. Nitrogen is the main nutrient found in manure; carbon is the main element found in bedding material. The challenge is to ensure the proper proportions of carbon and nitrogen needed for successful composting. 

Carbon to Nitrogen Ratios
MaterialC:N Ratio
Horse manure20-40:1
Grass clippings20-25:1
Horse manure w.bedding30-60:1
Grass hay40-100:1
Wood chips/sawdust150-500:1

Carbon-to-Nitrogen Ratio (C:N):  This is very important since microbes need 20-25 times more carbon than nitrogen to remain active. A ratio of 25:1 and 30:1 is ideal.  If the ratio is too high (insufficient nitrogen), decomposition slows.  If the ratio is too low (too much nitrogen), it will be lost tothe atmosphere in the form of ammonia gas causing odor problems.

The carbon-to-nitrogen ratio (C:N) of a material is an estimate of the relative amounts of these two elements. The approximate ratios for some materials commonly added to compost piles is shown in the table.  C:N ratios represent comparative weights.  So, 20 lbs of horse manure/bedding would contain 1 lb of nitrogen, while 500 lbs of sawdust would contain 1 lb or nitrogen. A mixture of one part manure with two parts bedding (by volume) usually gives a reasonable mix for rapid composting. However, the amount and type of bedding can alter the C:N ratio and influence the management needed for successful composting (refer to Bedding Tips)

Benefits of composting

  • Kills intestinal parasite eggs and larvae
  • Destroys weed seeds
  • Reduces flies by eliminating their breeding ground
  • Reduces odor
  • Reduces volume of manure
  • Improves soil structure (permitting better root growth) especially in sandy or clay soils
  • Produces an attractive product to use, give away, or sell to others