Step 4: Calculate volume
The next step is to calculate your storage needs to help build the appropriate volume. If you are building a multiple bay system (strongly recommended), you will need to decide the appropriate size for each bin. There are helpful example calculations below as well as an interactive calculator for your convenience.
Choosing the size of your compost system is probably the most difficult and important decision you will make when building a system. We have many farmers ask us, “How big should I build this thing?” and unfortunately there isn’t really a clear answer. System size is really dependent on the following:
- Farm size
- Number of animals on property
- Storage capacity
- Length of storage time needed
- Type of paddock footing used
- Type of bedding used in stalls
- Ability to increase the number of animals on the property
- Average seasonal temperature
- Amount of waste generated each day
- Number of people cleaning your stalls (week day versus week end staff)
- Whether you own machinery for spreading
In order to effectively store your horse manure compost you need to be able to determine the approximate sizing of your manure bins. The following calculations are from the BC Environmental Farm Plan and should give you a good idea of how large your system needs to be. These are general guidelines to follow and are over-estimated in order to compensate for bedding material added to the system. You know your property better than anyone and can decide for yourself what the most appropriate measurements will be for your system.
Most important is to remember it is better to overestimate the amount of volume needed than to underestimate it. Leaving extra room to allow for turning will make managing your manure much easier. You may also consider building your system in a location on your property where you can expand the system if needed.
Try it Yourself:
Daily manure production = x = litres/day
Manure storage requirements = x = m3
Effective depth of storage = – = m
Storage length = / / = m
*Freeboard safety: this step in the calculation process is to ensure that the calculated storage length allows for the appropriate volume to be contained while allowing for space between the top of the pile and the top of your system.
Here are some example size calculations.
For a horse property with 5 horses and 6 months of storage required (in metres).
1. Daily manure production = number of horses x horses’ daily manure production rate
Daily manure production = 5 x 26.1 = 130.5 litres/day
Divide by 1000 and round to one decimal place = 0.1 m3/day
2. Manure storage requirements = daily manure production x days of storage required
Manure storage requirements = 0.1 x 180 = 18 m3
3. Effective depth of storage = chosen storage depth freeboard safety
Effective depth of storage = 2 – 0.2 = 1.8 m
4. Storage length = total storage required / effective depth of storage / storage width
Storage length = 18 / 1.8 / 3 = 3.3 m
For a horse property with 5 horses removing 4 wheelbarrow loads per day and 6 months of storage required (in feet).
1. Daily manure production = wheelbarrow loads per day x size of wheelbarrow
Daily manure production = 4 x 4 ft3 = 16 ft3 per day
2. Manure storage requirements = daily manure production x 180 days
Manure storage requirements = 16 x 180 = 2880 ft3
3. Effective depth of storage is 5ft with 10ft x 10ft bins
4. Storage length = total storage required / effective storage depth / storage width
Storage length = 2880 / 5 / 10 = 57.6 ft
Bin dimensions should be 10ft wide x 57.6 ft long x 5 ft high