Features
On Farm Composting
What Is Composting?
Composting is often defined as aerobic decomposition of organic materials into a crumbly, dark, soil-like amendment, rich in ‘stable humus’ – the foundation of a fertile soil. Typically, none of the original materials can be easily identified by the end of the composting process, indicating a well humified (humus rich), finished compost.
The production of compost ‘on-farm’ is an ideal way for farmers and growers to make use of their waste materials and produce a valuable soil conditioner; rich in microbial life, organic matter and essential nutrients. Various organic waste materials produced via farming activities such as farm yard manure, slurry, vegetable and crop wastes, stubble, wood chips/shavings, spent bedding, spoiled hay and hedge prunings can all be used to produce quality compost. The different methods of composting include:
- Vermi-composting – involving the use of composting worms
- Passive composting – is the slow, unmanaged degradation of plant wastes; such as adding mulch to soil or static compost piles
- Thermophilic composting – a more rapid breakdown of organic material where the compost pile is actively managed and becomes hot in order to sterilise weed seeds and pathogens. This article provides the basic information you need to make thermophilic compost from your farm organic wastes.
Making Good Quality Compost On-Farm
The fundamental rules of composting are the same whether you are making a small pile for your own garden or a large windrow for commercial production. There are a host of intricate, technical and scientific details that can be considered when making compost, but the average farmer must learn to make do with available materials and time – time being a precious resource on most farms. Good compost must have a balance of carbon-rich/woody materials and nitrogen-rich/green leafy matter or manure-based materials. Selecting the correct mix to give a starting carbon:nitrogen (C:N) ratio of about 30:1 (meaning 30 parts carbon to 1 part nitrogen) will optimize the composting process (refer Table 1).
| Ingredient | %N | %C |
|---|---|---|
| High in carbon | ||
| non-legume hay | 1.3 | 42 |
| tree prunings | 1.0 | 50 |
| straw | 0.7 | 56 |
| woodchip/shavings | 0.1 | 50 |
| newspaper | 0.04 | 25 |
| High in nitrogen | ||
| blood and bone meal | 13 | 42 |
| vegetable wastes | 3 | 30 |
| chicken litter | 2.7 | 38 |
| grass clippings | 3.4 | 58 |
| cattle (dairy) manure | 2.7 | 48 |
| horse manure | 1.6 | 48 |
The C:N ratio of your starting mix can be determined when you know the C and N values and weight of the product you are using. To calculate the C:N ratio, divide the total carbon % of your selected ingredients by the total nitrogen % of your selected ingredients. You can have as many ingredients as you like:
For example, if you were using 3.5 T cattle manure + 800 kg straw + 10 kg blood & bone meal:
A C:N ratio of 21:1 is too low, meaning there is too much nitrogen in the mix and more carbon is required. If you were to add an additional 1.9 T of woodchips to the above mix you would then have the ideal C:N ratio as per below:
If the equations above have left your head spinning a little and you prefer something a little less mathematically challenging; a good general rule is to use about 2 parts high carbon materials to 1 part high nitrogen materials. Either way, the trouble shooting table further below will help you assess how adequate your mix is once the compost gets going (refer Table 2).
Constructing The Pile
Mix all the materials and construct a pile that is between 1.5 and 2 metres high and 2 to 3 metres wide. It can be as long as you need. Every 1 metre in length will make about 3 cubic metres (m3) of compost at those dimensions. If the pile is too small, it will not have enough body or mass to kick start and retain the heating process; while larger piles will be more difficult to manage. At the time of construction, you may also need to add water as you mix the ingredients together – the ideal moisture content is around 50%. To check this, take a handful of compost and squeeze; the sample of material should feel moist and glisten with water, but shouldn’t drip excess water.
Turning The Compost Pile
After a day or two, check the temperature in the pile. It should be increasing in temperature and reach between 50 and 65oC (this is now considered a thermophilic compost). Use a shovel to dig a hole in the middle of the pile. You will probably notice steam rising and the compost should feel uncomfortably hot. You can check the temperature accurately with a thermometer. If the temperature is above 70oC, turn the pile immediately. When turning the pile, ensure the materials from the outside of the pile are placed on the inside.
This can be achieved by rolling the pile over using a front-end loader or lifting the pile and dropping in its original place using an excavator. A gentle mixing is much more preferable than an aggressive, vigorous turning which will disrupt the growth of fungal hyphae and reduce microbial diversity in the compost. If the pile has not heated up within 1 week, it is likely there are insufficient green/high nitrogen inputs in the pile and they should be added and mixed in.
Monitoring The Temperature
Keep monitoring the temperature on a weekly basis and turn the pile each time the temperature reaches 65-70oC. Try and turn the pile more often during the first half of its life, and less often in the second half. The pile will probably need to be turned at least three times before the compost is ready for use but may need up to six or more turns, depending on the materials used. It is important for the compost pile to reach at least 60oC to kill any unwanted pathogens/weed seeds and to break down all the material properly. It must not get hotter than 70oC though, as this will reduce the nutrient and carbon value of your compost, kill beneficial decomposer organisms and run a risk of catching on fire.
Once the pile has stopped producing heat, let it cure and mature entirely undisturbed for at least 6 months. If the pile is well protected from the elements, even a 12 month maturation can be beneficial. This involves planning ahead for upcoming seasons with the goal of applying the compost produced this year, in another 1-2 years time. Once this cycle is set up and established though, it will be self sustaining.
Aeration And Moisture
To ensure oxygen can move throughout the compost heap, it is important to include a range of different sized and shaped materials and also to turn the pile when it heats up. Remember that large pieces of woody material will take much longer to break down than smaller chips or shavings; but they do help to maintain structure in the pile (preventing slumping) and hence, encourage oxygen diffusion. Oxygen is critical to production of quality compost and if the compost goes anaerobic (reduced oxygen), the microbial and nutritional quality of the compost will rapidly decline. Ideally, the water content should be around 50% - it should feel like a moist sponge but excess water should not drip out when you squeeze it in your hands.
To make sure the pile stays wet enough during the composting process, you may need a water supply to keep moisture up to the pile or if it is too moist, turn it and add dry materials to help soak up the excess water – also refer to ‘Trouble Shooting’ below.
Equipment And Location
If making a large amount of compost, you will need machinery to turn the pile. A front-end loader or excavator/grabber is ideal. Alternatively, you may consider using a contractor. You will need to dedicate and set aside an area specifically for the life of the composting and maturation process. The area you identify should be relatively flat and free of stones, tree stumps, drainage lines and weeds. There should be enough room for machinery to turn the compost. The pile should be located so it will not contaminate adjacent land or waterways via wind drift and water runoff.
If possible, the compost can be moved into some woodland or on the border of a woodland during the ‘undisturbed maturation’ process. These very fungal rich environments provide an ideal microclimate for maturation and encourage beneficial fungal growth in the compost. You may need to cover your pile during the winter months if excess rainfall is expected. The smaller a pile is, the more important this becomes – larger piles have a greater ability to absorb and retain rainfall without becoming waterlogged and anaerobic.
| Problem | Cause | Remedy |
|---|---|---|
| Excess water running off | Too wet | Add dry materials or let pile dry out a little |
| Bad smell | Anaerobic conditions | Add larger materials and turn more often |
| Ammonia smell | C:N ratio too low | Add extra high-C materials |
| Clumping | Compost is too wet | Add dry materials and turn |
| Pile won’t get hot after construction or the compost process does not appear complete | C:N ratio too high | Add high nitrogen materials but avoid synthetic fertilisers |
| Moisture is incorrect | Adjust accordingly | |
| Too little oxygen | Turn pile |
When Is The Compost Ready?
Intensive commercial composting sites can produce compost in about 8 weeks; but typically, low-tech, on-farm composting takes longer. Depending on the ingredients, it may take around 6 months, but as previously mentioned, a further undisturbed maturation period is desirable. The composting process takes longer if there is insufficient moisture or too much carbon rich material. It is very important not to use compost before it is ready as it will scavenge nutrients from the soil (particularly nitrogen) to finish its composting process leaving many soil nutrients unavailable to plants.
When the compost is ready it has the following distinct characteristics:
- Smell – nice earthy smell, with no putrid, sour or rotten stench
- Feel – moist and earthy, not wet, sloppy or dry and powdery
- Appearance – original organic materials are not distinguishable. The colour of the compost should be dark, chocolate brown, not black. If it is black, the pile most likely became too hot
- Temperature – finished compost should be at ambient temperature
- C:N ratio – mature compost has a C:N ratio of around 12-15:1 (a laboratory test for this costs around £15 or €20).
- Microbial Analysis – Laverstoke Park Laboratory can also provide an assessment of compost quality by measuring bacterial and fungal biomass, protozoa and nematode numbers as well as aforementioned C:N ratio.
Benefits Of Compost
There are many benefits to soil health when using compost in organic, biodynamic and conventional farming systems. One of the most important benefits from compost is the addition of living microbial biomass and organic matter to the soil. Organic matter provides food for soil life, holds nutrients in the root zone and increases the stability of the soil so that it becomes more resistant to erosion and compaction. Good quality compost can also be used as a base ingredient for the production of liquid compost extracts and compost teas. This liquid form of beneficial biology can be sprayed over the foliage or drenched down into the soil to repopulate fields with this invisible workforce.
Micro-organisms that thrive in quality compost, compost tea and farming soils perform a plethora of beneficial functions in the soil and increasing the soil microbial community improves nutrient availability, improves soil structure and increases the plants resistance to disease and stress. Compost also improves soil-water dynamics, adds nutrients in a stabilised, slow release form (thereby reducing fertiliser requirements) and supplies, feeds and encourages a wide range of soil micro and macro organisms which are crucial to supporting healthy, self sustaining farming soils.
A Soil Association report in the UK finds that Community Supported Agriculture (CSA) offers many benefits to members,
communities, local economies and...
