Calculates daily volatile solids (VS) excretion in manure (kg VS/head/day). VS represent the organic fraction of manure dry matter, including both biodegradable and non-biodegradable organic material. VS is a key intermediate variable required for estimating methane (CH4) emissions from manure management systems under IPCC methodologies.
Usage
calc_volatile_solids(
ration_intake,
ration_digestibility_fraction,
ration_urinary_energy_fraction,
ration_ash
)Arguments
- ration_intake
Numeric. Average daily dry matter intake of feed (kg DM/head/day).
- ration_digestibility_fraction
Numeric. Average digestibility of the feed ration, expressed as ratio of digestible to gross energy content (fraction).
- ration_urinary_energy_fraction
Numeric. Fraction of feed's gross energy that is excreted in urine (fraction).
- ration_ash
Numeric. Average ash content of feed, calculated as a fraction of the dry matter intake (kg ash/kg DM).
Value
Numeric. Total volatile solids (VS) excreted per animal per day, representing the organic material in livestock manure and consisting of both biodegradable and non-biodegradable fractions (kg VS/head/day).
Details
The IPCC recommends estimating volatile solids (VS) excretion from feed intake and digestibility when country-specific average daily VS excretion rates are not available. The core relationship is provided in IPCC Equation 10.24 (Volatile solids excretion rates), which estimates daily VS excretion as a function of:
Gross energy intake (gross_energy_intake, MJ/day)
Digestibility of the diet (ration_digestibility_fraction)
Urinary energy expressed as a fraction of GE (ration_urinary_energy_fraction)
Ash content of the diet (ration_ash, fraction of dry matter)
A conversion factor representing the average gross energy content of dry matter (18.45 MJ/kg DM)
The general structure of Eq. 10.24 partitions gross energy intake into digestible energy, urinary losses, and ash, and converts the remaining organic matter into volatile solids using the energy density of dry matter.
Implementation note. This function applies an algebraically simplified formulation from Equation 10.24 of IPCC.
In this implementation, the function takes ration_intake directly
as an input. It can be calculated upstream with
calc_ration_intake as a function of energy requirements and
the energy content of the diet.
$$ dry\_matter\_intake = \frac{gross\_energy\_intake}{diet\_gross\_energy} $$
This reflects the use of ration-specific energy content upstream and avoids assuming a fixed gross energy density of 18.45 MJ/kg DM, as in the IPCC default approach.
The volatile solids excretion is then calculated as:
$$ volatile\_solids = dry\_matter\_intake \times (1 - diet\_digestibility\_fraction + urinary\_energy\_fraction) \times (1 - diet\_ash) $$
The resulting calculations are algebraically equivalent to the IPCC approach and fully consistent with Equation 10.24.
This function is part of the run_emissions_manure_module().
References
IPCC. (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 10: Emissions from Livestock and Manure Management. Equation 10.24.
IPCC. (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 10: Emissions from Livestock and Manure Management. Equation 10.24.