New study on ammonia losses from dairy housing systems
New measure methods allow for more precise figures for ammonia emissions from dairy housing systems.
Air pollution entails a number of negative consequences for both human health, nature and the environment. One of the major Danish challenges is ammonia (NH3) and other nitrogen compounds. Thus, the Danish Environmental Protection Agency estimates that more than half of the Danish natural resorts receives more nitrogen via the atmosphere than they are able to tolerate.
The agricultural sector is responsible for the major part of ammonia emissions to the atmosphere. The ammonia mainly comes from barns, manure stocks and the distribution of manure. Traditionally, cubicle barns for dairy cows are equipped with slatted floors beneath which slurry channels collect the excreted slurry. Volatilization of ammonia in these barns primarily takes place via the slurry channels and the slatted floors.
In an attempt to reduce ammonia emissions, new types of cubicle barn floors have been developed, allowing for a reduction of ammonia emissions from the slurry channels. Among these are different types of sloped concrete floors with urine drains in the walking alleys. The manure is removed every 2 hours using manure scrapers. Dutch studies have indicated that floor designs aiming at continuous urine drainage and frequent removal of solid manure may reduce ammonia emissions with as much as 50 percent compared to barns with slatted floors. These studies have formed the basis for an estimated Danish ammonia emission value for barns with solid drained floors with scrapers and drain.
The Danish Environmental Protection Agency has evaluated possible ammonia reducing initiatives in barns with a view to determining the so-called BAT requirements (Best Available Technology); and based on e.g. the estimated low ammonia emission from barns with solid drained floors, threshold values for dairy barns have been determined.
However, only few and sporadic ammonia measurements have been accomplished in Danish dairy barns. In practice, it is difficult to measure ammonia emissions from naturally ventilated barns, resulting in uncertainty as to which floor types and technologies are the best in relation to reducing ammonia emissions.
A new study will remedy this. Applying newly developed, state-of-the-art equipment, researchers from the Danish Technological Institute, SEGES and Aarhus University have examined ammonia emissions in eight cattle barns; four of these with slatted floors and four with solid drained floors.
Two different floor types
In barns with slatted floors, the slurry is collected in slurry channels beneath the slatted floor, where the slurry is recirculated and mixed daily. Typically, slurry channels have a capacity of as much as two months’ slurry production in the barn. When the slurry in the channels reaches a certain height, it is pumped to an outdoor storage tank leaving a minimum of 40 cm of slurry behind to allow recirculation of the remaining slurry.
In barns with various types of solid floors, the floor construction allows the urine to be continuously drained off the floor surface and transferred to an outdoor storage tank from which only limited emission takes place. Alternatively, floors may be constructed with reduced slotted areas, which ensure minimum ventilation in the slurry channel, resulting in reduced ammonia emissions. The solid manure is typically scraped into a slurry channel located at the end of the alley and from here, it is transferred to the out-door storage facilities. The floor is automatically scraped 12 times a day. The idea is that the urine, containing the major part of the urea, is removed from the barn to the out-door tank as quickly as possible in order to minimize emissions.
Dutch studies from the early 1990’s demonstrated that ammonia emissions from barns with solid drained floors are up to 50 percent lower compared to barns with slatted floors. However, the Danish study did not confirm this.
Differences between experimental barns and practical conditions
The Danish measurements show that on average only minor differences exist between ammonia emissions from the two systems. The measurements in barns with slatted floors thus demonstrated an average annual emission of 1.2 kg ammonia-nitrogen per m2. The corresponding figure for barns with solid drained floors is 1.0 kg, which is far from the 50 percent reduction suggested by previous Dutch studies. However, subsequent correction for variations in feeding and production areas result in an average annual emission of 1.16 kg ammonia-nitrogen per m2 for barns with slatted floor. The corresponding figure for barns with solid drained floors is 0.89 kg per m2, i.e. a difference of 23 %. The difference is statistically significant.
For comparison, the current Danish standard ammonia emission values for cubicle barns with slatted floors and solid drained floors are 1.34 and 0.67 kg ammonia-nitrogen per m2 per year, respectively.
In cooperation with Anders Peter Adamsen (previously employed at Aarhus University, now at SEGES), Senior Advisor Peter Kai, Department of Engineering, was in charge of the study and he provides a plausible reason for the lacking difference.
- The Dutch studies were carried out in experimental facilities under very controlled – almost laboratory-like – conditions, whereas our study was accomplished in ordinary production barns and under natural conditions, Peter Kai explains.
- When the floors in experimental barns are scraped, we expect them to be free from manure thus ensuring that no further emissions take place. The situation is completely different under practical conditions: the scraping equipment may be worn, floors are uneven or may have cavities, and you will not achieve the desired effect. Peter Kai further points out that the Dutch experiments were accomplished in barns with specific floor types. The Danish definition of a solid drained floor allows for different types of solid floors. The project resources only allowed the study of three types of solid drained floor, whereas a report prepared by SEGES describes 12 different types of low-emission floors, of which nine are comprised by the definition of solid drained floors.
Other factors may come into play
The studies were accomplished using recently developed and very accurate measuring equipment able to detect even microscopic amounts of ammonia. Contrary to previous studies, the researchers now have significantly more measurement data.
- The development of the measuring equipment provides new and improved opportunities for us to develop floor and barn types that help reduce ammonia emissions, Peter Kai explains. The researchers have better opportunities to detect precisely where ammonia emissions take place, and thus how to improve housing systems.
Peter Kai emphasizes that other factors may affect ammonia emissions, such as e.g. protein contents in the feed rations.
However, measuring ammonia emissions under actual conditions does not come free. Within the framework of the present project, the researchers had to develop measuring methods, resulting in major additional costs. Carrying out all measurements in eight barns amounted to approx. 7 million DKK. The project is funded by the Milk Levy Fund (Mælkeafgiftsfonden), the Danish Agricultural Agency and the Danish Environmental Agency.
Subsequently, the Milk Levy Fund has granted an amount of money to AU and SEGES in order for researchers to carry out a study to document the impact of slurry acidification on ammonia and methane emissions. However, there are no funds to accomplish studies in barns with different floor types and manure handling systems, which is a shame, says Peter Kai:
- The project measurements demonstrate that ammonia emissions from the most common floor type in dairy housing systems is lower than expected. If this is also true for other floor types, then the Danish agricultural sector may meet the requirements as to reducing ammonia emissions sooner than expected.
Senior Advisor Peter Kai, Department of Engineering, Aarhus University. Tel. +45 9350 8622, e-mail: Peter.Kai@eng.au.dk
The study is published in a DCA report, available for free download here:
Peter Kai, Anders P. S. Adamsen, Morten L. Jensen, Pernille Kasper, Anders Feilberg, 2017: Ammonia emission from Danish cubicle barns for dairy cows - Effect of floor type and manure scraping. DCA report no. 110, 2017