On-farm composting – getting it right

David Shambrook

Agriculture Victoria Dairy Extension Officer

Farm effluent and manure along with left over materials such as wasted feed, wood chips, rice hulls, fouled bedding materials and tree prunings are all materials that could be used to produce a compost and be recycled back on the farm.

What are the benefits of producing compost? Compost, if it is made correctly will allow you to:

  • handle, store, transport and spread organic by-products back to land
  • recycle high carbon low nitrogen materials back to the land, without tying up as much soil nitrogen while they are going through biological processes
  • produce a safe, stable soil amendment with slow release nutrients in organic forms
  • improve soil fertility, soil structure and general soil health.

If you choose on-farm composting, then you need to plan to do the process properly which requires the use of costly, specialised equipment, an area of land set aside for compost making and storage of materials, and the time to perform the tasks required.

Additionally, you need to consider that the end product will have a lower volume, lower carbon and nitrogen than the original materials with high C:N ratios.

If you believe the benefits of containing and recycling the organic by-products generated on-farm by producing compost outweigh the costs of managing the complex production process, then what do you need to know for it to be successful?

Composting is a biological process, carried out by microorganisms that are naturally present in the environment, therefore no special inoculants are required. What you need to provide is organic materials in the right proportions, with moisture, and the microbes will do the rest.

Understanding the conditions required by composting microbes is important for successful composting.

Microorganisms have three basic needs and when these are provided, the composting process will proceed, and the mix will heat up as required. These needs are:

  • oxygen (greater than 5 per cent)
  • adequate moisture (45 to 65 per cent moisture)
  • suitable food supply (material with carbon to nitrogen ratio of 30-40:1).

If you provide the above conditions the composting process will begin, and the pile of material will start heating up. This part of the process is called the thermophyllic stage where intensive decomposition of organic residues is occurring, reaching temperatures of between 45°C and 65°C.

Temperature is key factor in composting. The use of a gauge to monitor the temperature and regularly checking moisture content by squeezing handfuls of the material will help maintain appropriate temperatures.

The temperature needs to hold for at least three days to ensure sterilization of pathogens, diseases and weed seeds occurs. At the end of this stage, all the readily available organic substrate has been exhausted and the temperature cools down allowing the compost to cure or mature.

The whole process could take several months depending on how quickly the material heats up and when all the readily available substrate has decomposed.

The whole composting process needs to be monitored, making sure the conditions for the microbes is kept reasonably constant for them to breakdown the material.

Providing a balance of smaller and larger particle sized materials will allow effective aeration to be achieved for microbes to access oxygen. Regular turning of the material for aeration and addition of water to maintain the moisture levels, particularly as moisture is lost in the heating process, will also aid the process.

On-farm production of compost is best suited to using what is called the windrow method.

This involves creating windrows of the organic material that are around 1.5 metres high and 2 to 3 metres wide at the base. Ideally the site should have a level compacted surface such as concrete, crushed rock or gravel or compacted soil.

This method allows easier turning of the material and watering, as required, to maintain the temperature within the windrow.

When selecting a site for compost making, also consider the potential for runoff, odour, groundwater reserves and movement of windborne particles.

Before embarking on large scale production of compost we recommend you do a test stack or small windrow, using waste organic materials you have ready access to on the farm.

Keep a record of what you do and what the compost was like at the end of the process. This will enable you to see if the materials you have will provide the right carbon to nitrogen ratios and enable the correct proportions to be used.

If you intend to bring in green waste materials for the compost process, you may need to seek Environmental Protection Authority approval or designing, constructing and operating composting facilities.

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