Litter composition and ammonia emission in aviary houses for laying hens: Part II, modelling the evaporation of water

Experimental research was carried out with laying hens of 47-60 weeks of ag e to validate a physical model of the evaporation rate of water from litter in a tiered wire floor aviary system. Variation of the evaporation rate of water from the litter was achieved by varying air velocities above the lit ter between 0.07 and 0.28 m/s, by naturally varying outdoor climatic weathe r conditions and by removing manure on the belts once a week, once per day, or twice per day. An evaporation model was developed and used to predict t he water content of the litter on a certain day. The water content increase d with 126.8 g/kg litter (S.E. 19.4) due to the water input by the faeces d ropped in the litter by the hens. The evaporation rate of water from the li tter was positively influenced by the air velocity (v(air)(0.287)) and the difference between the water vapour pressure in the litter and the water va pour pressure of the air above the litter. The water activity of the litter was estimated to be 0.86 (S.E. 0.07) and decreased the saturated water vap our pressure in the litter. The water vapour pressure of the indoor air hig hly depended (79%) on the water vapour pressure of the outside air. It was predicted that in this way drying conditions above the litter worsen from A pril to October under Dutch circumstances, but that this can be compensated by an increase of the litter temperature and higher air velocities. The em ission of ammonia was modelled with the following influencing parameters: m anure removal interval (0.76%/h), indoor temperature (8.1%/degrees C), wate r content of the litter (0.32%/g/kg) and air velocities above the litter (1 03%/m/s). The mean emission in the case of daily removal of the manure on t he belts amounted to 2.85 mg/h/hen. (C) 1999 Silsoe Research Institute.