In order to make conversions, the chemical composition of the different manures is needed. The American Society of Agricultural Engineers (ASAE) provides a set of equations for predicting nutrient excretion (nitrogen and phosphorus) and dry matter depending on livestock species (ASAE standards S384.2). Eurostat has based this summary on typical or average values of manure excreted which could become obsolete due to changes in animal genetics, performance potential, feeding program strategies and available feeds. Nutrient content of manure varies depending on source (type of animal, animal diet), moisture content, storage, and handling methods. In addition to livestock excreta, manure and processed, waste water collected may contain other materials, soil, animal bedding, waste feed, waste milk, weed seeds, etc. Dairy, beef and swine manure may be either solid or liquid. Horse and poultry manures are solid.
Solid manure
Corresponds to farmyard manure or the separated solid fraction of manure having at least 20% dry matter
Liquid manure
Corresponds to slurry or separated liquid fraction of manure with less than 20% dry matter (80% or more of water content).
Convert dry weight to wet weight
Figure 73 – Example for solid bovine (for beef) manure
The dried basis is detailed because it is necessary to dry the sample in the lab for analysis. To convert back to a wet-weight "as received" and/or "as excreted" the moisture content (%) must be known.
wet-weight value = dry-weight value x (1 – (% moisture100))
wet-weight value = 1.7 x (1 - (69.5/100))
wet-weight value = 1.7 x (1- 0.695)
wet-weight value = 1.7 x 0.305
wet-weight value = 0.52% total N
Convert percentage to Kg/tonnes
In the above example, the total N content of the solid beef manure is 0.52% total N on a wet-weight, or as-received, basis. This means that there is 0.52 kg of total N in every 100 kg of manure. There are 1,000 kg in a tonne. Therefore, there are 5.2 kg total N in 1,000 kg of manure. kg/tonne = value (%) x 10 kg total N/tonne = 0.52 x 10 kg total N/tonne = 5.2
Convert percentage to Kg/m3
Figure 71 – Example for liquid swine manure
The total N content of the liquid manure is 0.37% total N on a wet-weight, or as-received, basis. This means that there is 0.37 kg of total N in every 100 kg of manure; or 3.7 kg total N in 1,000 kg. To convert liquid manure from a weight to a volume, estimate the density. The density of water is 1,000 kgm3. However, the higher the dry matter content of the manure, the lower the density of the manure. Since the liquid swine manure has a very low solids content, we can assume that the density of the liquid swine manure is very close to the density of water. For the purpose of this calculation, assume the density of the liquid swine manure is 1,000 kgm3.
To calculate the volume of 1,000 kg of manure:
Density = MassVolume
1,000 kgm3 = 1,000 kgVolume (m3)
Volume = 1,0001,000 m3
Volume = 1.0 m3
Since there are 3.7 kg total N in 1,000 kg of manure and 1,000 kg equals 1.0 m3 of manure, then there are 3.7 kg total Nm3 of manure. Therefore, the simple factor from percentage to kgm3 is 10, as follows:
kgm3 = value (%) x 10