Oriënterend laboratoriumonderzoek naar ammoniakemissie uit bodempakketten voor vrijloopstallen = Laboratory study of ammonia emission from bedding materials of freestall dairy cattle houses

In the Netherlands there is growing interest amongst dairy farmers in new housing systems in which animal welfare and health are improved. A promising system in this area is a loose housing system (without cubicles) where cows have a large area with a soft bedding where they can both being active and rest, so called freestalls. Although these systems are already applied in the USA and Israel, little is known about the environmental impacts, and particularly the ammonia emission. The aim of this study was to get some first impressions of the suitability of different bedding materials, especially concerning ammonia emission. The ammonia emissions of simulated urinations were measured in a laboratory set up with several bedding materials. As non degradable materials, two types of sand with larger and smaller average particle size and one type of rubber shaving were tested. As degradable materials freshly produced press screwed manure (the solid fraction), without (1) and with (2) an added mixture of sawdust and wood chips, composted press screwed manure (3) and (4) mud (peat soil/clay) originating from the small channels in the grasslands in an area with a peat soil with a top soil layer of clay. One week before the laboratory experiment, each of the bedding materials was mixed with fresh dairy cattle feces, urine and press screwed manure to get a quick simulation of the excreta accumulation in beddings in freestalls. Into the non degradable materials less feces and less screw pressed manure were added to simulate an on farm partly removal of feces from the resulting beddings. After preparation the bedding-excreta mixtures were kept one week in boxes in a ventilated house, with similar conditions as in a cow house. After this week, the ammonia emission from a simulated urination was determined in a laboratory set up. The degradable variants were tested both after manually pressing (higher density) and without pressing (lower density) the bedding mixtures in the laboratory set up. Ammonia emissions were higher with the non degradable bedding materials than with the degradable materials. The emission of the mud bedding mixture was low after 4, 24 and 72 hours. The emission of the mixture of screw pressed manure, sawdust, and wood chips with added excreta was very low after 4 hours. However after 24 and 72 hours the higher density variant showed a remarkable increase of ammonia emission while the low density variant did not. Between the tested bedding variants substantial differences in ammonia emissions were measured. Only a quick and short simulation was done to get first impressions. In reality, longer term accumulation of excreta in the beddings may result in build up of layers, silting up and different conversion rates in the freestall beddings. This may result in higher or lower emissions. The ranking of bedding materials may change as a result of this. Further research, also on other gaseous emissions like greenhouse gasses, in real cow barns is recommended to study this time and conditions dependent phenomena in more detail