Production of carbon dioxide in a fattening pig house under field conditions. II. Release from the manure

Carbon dioxide (CO₂) release from manure was investigated under field conditions in one of the compartments in a mechanically ventilated fattening pig house. The potential of CO₂ release was tested in the emptied compartment by imposing high ventilation rate and measuring CO₂ concentrations in the incoming and exhaust air. When the compartment was filled with pigs, a model of tranquil CO₂ exhalation rate (TCER) was used to estimate the part of CO₂ produced by animals, in addition to the measurement of CO₂ concentrations and ventilation rate. Useful data were extracted from 135 days of continuously measured field data obtained when the housing system was in steady-state. The CO₂ release per m² of pit surface was 18.4 and 25.8 g h⁻¹ m⁻² in the emptied pig compartment during the impulse and pulse ventilation rate tests, respectively. It ranged from 1.1 and 116.7 g h⁻¹ m⁻² and averaged 42.1 g h⁻¹ m⁻² during the 135-day continuous field measurement. In 128 of the 135 days when the compartment was filled with pigs, the mean CO₂ release from the manure reached an average of 37.5% of the TCER by pigs, instead of less than 5% believed by many researchers. The maximum CO₂ release rate in 2-h steady-state measurements was 94% of the TCER by pigs. This research demonstrated that, in the previous knowledge, there might be a serious underestimation of the CO₂ release from the manure in pig houses. The total pig weight, manure temperature and ventilation rate were found the most important variables related to the CO₂ release. A mathematical model was developed to estimate the CO₂ release as a function of these three variables with R²=0.525.