Ammonia emissions from organic housing systems with fattening pigs

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1 Available at journal homepage: Research Paper: SE Structures and Environment Ammonia emissions from organic housing systems with fattening pigs Sonya Georgieva Ivanova-Peneva a,, Andre J.A. Aarnink b, Martin W.A. Verstegen b a Department of Animal Nutrition and Technology, Agricultural Institute, 3 Simeon Veliki Blvd., 9700 Shumen, Bulgaria b Researcher Livestock Environment, Animal Sciences Group van Wageningen UR, Animal Production Division, P.O. Box 65, 8200 AB Lelystad, The Netherlands article info Article history: Received 21 March 2007 Accepted 13 November 2007 Available online 22 January 2008 The aim of this study was to determine the level and variations in ammonia emissions from buildings and outside yards, with different manure removal systems, for organically raised fattening pigs. Ammonia emissions were determined at three farms with organically raised pigs. Amongst other differences, farms mainly differed in manure removal system at the outside yard. Measurements were carried out during two measuring seasons, with two categories of pigs: fatteners of 45 and 80 kg. Excreting behaviour was analysed by video observations and ammonia emission was measured by the ventilated chamber technique. There were clear differences in ammonia emission between farms (probability, Po0.001), varying between 0.0 and 7.7 g d 1 m 2 from the buildings and between 3.6 and 17.6 g d 1 m 2 from the outside yards. Location (inside/outside) and degree of fouling of the floor area also had significant effects on ammonia emission (probability, Po0.001). Differences in ammonia emissions between farms were probably mainly related to the manure removal system, design of the building and frequency of cleaning of outside yard. The farm with daily scraper cleaning and the farm with the slatted floor system had significantly lower emissions than the farm with bi-weekly manual removal of manure from a solid floor. & 2007 IAgrE. Published by Elsevier Ltd. All rights reserved. 1. Introduction One of the main reasons for promoting organic farming throughout Western Europe (and in the Netherlands) is the claimed reduction in environmental pollution. However, scientific evidence of the environmental impact of raising organic livestock farming is scarce. According to the EC regulation No. 2092/1991 (EEC, 1991) on organic farming, the area available per pig must meet certain minimum requirements, which is larger than for conventional pig farming, and housing must be supplemented with an outside yard. In the Netherlands the outside yard is generally a paved yard and this is where most urinations and defecations take place. The yard therefore becomes a significant source of ammonia volatilisation and as a result the emissions might even exceed those from conventional pig production systems. Keck et al. (2004) estimated that emissions from the open yard clearly dominated the emissions from the accompanying building, accounting in the summer for over 80% of total ammonia emissions. An additional problem in organic pig production, related to ammonia emissions, is that free amino acids cannot be added Corresponding author. addresses: ivanovapeneva@yahoo.com (S.G. Ivanova-Peneva), andre.aarnink@wur.nl (A.J.A. Aarnink), martin.verstegen@wur.nl (M.W.A. Verstegen) /$ - see front matter & 2007 IAgrE. Published by Elsevier Ltd. All rights reserved. doi: /j.biosystemseng

2 413 to the diet. Thus, in order to supply sufficient essential amino acids with dietary proteins, high levels of dietary protein may be added. With an increased protein content in the ration, nitrogen efficiency in the diet decreases and this may lead to a greater emission of ammonia. This has been confirmed by research in Denmark, where Dalggard et al. (1998) reported that organic pig production has a lower N-efficiency and a higher N-surplus per kg meat than conventional pig production. Ammonia is an environmental pollutant (Hartung, 1992; Nielsen et al., 1991; van Breemen et al., 1982) which causes nitrogen enrichment of the soil, and affects groundwater, surface water and the air. This can have detrimental effects on ecosystems. Large amounts of ammonia are generated in areas of intensive animal production, such as in North- Western Europe. Strict regulations have been introduced in an attempt to curb its release. In order to reduce ammonia (NH 3 ) emissions the European Union has introduced an emission ceiling for each member state, according to Protocol of Göteborg (CLRTAP, 1999). The ceiling for the Netherlands is 128 kt NH 3 per year in 2010, which is approximately 40% less than the emission in 1980 (Sliggers, 2001), the reference year for the Dutch government. Pig production is considered responsible for about 38.2 kt per year or 27.5% of the total ammonia emission from livestock production systems in the Netherlands (RIVM, 2002). These data are based on conventional farming and many studies have been done with the goal of reducing ammonia emissions from conventional pig production units (Hartung & Phillips, 1994; Rom, 1995; Aarnink, 1997; Canh, 1998). By contrast, almost only a few studies have been carried out in outdoor or organic systems (Keck et al., 2004; von Wachenfelt & Jeppsson, 2006). Ammonia emission from straw bedding systems were better investigated (Amon et al., 2006; Groenestein & Van Faassen, 1996; Jeppsson, 1998; Mannebeck & Oldenburg, 1991). Gustafson and Svensson (2003) compared emissions raised from inside on deep-litter pigs and from outside on grazing pigs. Some other studies (Misselbrook et al., 1998, 2001; Monteny & Erisman, 1998) have investigated emissions from outdoor concrete yards used by livestock. But research in ammonia emission in organic pig production has not been carried out systematically. The aim of this study was to determine the level and variations in ammonia emissions from buildings and outside yards, with different manure removal systems, for organically raised fattening pigs. 2. Materials and methods 2.1. Housing The investigation on ammonia emission was done in two seasons (spring and autumn) and on three organic pig fattening farms in the Netherlands. The pigs were kept in groups, each of which had an inside area available for feeding and lying, provided with straw bedding. Each pen was connected to an outside yard for exercise and dunging. The layout of the housing is shown in Figs The pens and Feeder 1.60 Open space Outside yard Feeding passage Drinkers Fig. 1 Pen layout for fatteners on farm 1; all dimensions in m. Corridor Inside pen 2.35 Slatted floor Slatted floor 0.90 Outside yard 5.75 Feeders with drinkers 2.35 Drinker Fig. 2 Pen layout for fatteners on farm 2; all dimensions in m.

3 414 Feeder Drinker Passage Inside pen Outside yard 3.00 Scraper Feeder Feedeing through Passage Inside pen Outside yard Slatted floor Ventilator 4.80 Drinker Fig. 3 Pen layout for fattening pigs on farm 3: (a) 45-kg fatteners; (b) 80-kg fatteners; all dimensions in m. Table 1 Number of pigs per pen and area available per pig inside and outside the building Farm Season 45-kg fatteners 80-kg fatteners Pigs per pen Area inside (m 2 ) Area outside (m 2 ) Pigs per pen Area inside (m 2 ) Area outside (m 2 ) 1 Spring Autumn Spring Autumn Spring Autumn yards in the three farms differed in size. All farms had paved outside yards, which were made of solid concrete except for farm 2, where a part of the floor was slatted. On farms 2 and 3 the yards were roofed. On farm 1 each yard had a small unroofed area where the floor sloped down at a gradient of 8% towards the middle of the yard. On farm 2 the slatted floor was on either side of the yard and was 1.20 m wide just next to the building and 1.60 m wide on the opposite side with a solid part of 9.20 m in between. This part sloped down on both sides at a gradient of 5% from the middle towards the slats. On farm 3 there was a scraper running in the excreting area of the yard. The floor of the scraping area was approximately 100 mm lower than and sloped down to the centre in such a way that urine could flow to a pit below through perforations in the middle of the floor which also held the scraper s metal chain. There were differences in the frequency of cleaning the floor between farms. On farm 1, the manure from the outside yards was removed manually, with the help of a handcart, every 2 weeks. On farm 2 the solid surface of the outside yard was cleaned every week during the winter and spring and more frequently (almost daily) during summer and autumn. Manure from the under-floor gutter on farm 2 was removed every week. On farm 3, manure was scraped daily Animals The animals were fattening crossbred pigs (Large Whitex Dutch Landrace) as commonly raised in the Netherlands. On each farm, two pens were studied in detail. In one pen the average weight of the pigs was approximately 45 kg and in the other pen the average weight was approximately 80 kg. The pigs in each pen were of a similar age. The number of pigs per pen differed per farm, depending on the size of the pen and when they were measured (see Table 1). The pigs diets contained a minimum of 75% of products from organic arable farms. The feed was dispensed automatically. On farm 1 there was one feeder with four eating

4 415 places per pen. On farm 2 there were eight feeders available per pen with one feeding place each both for fatteners of 45 kg and for pigs of 80 kg. On farm 3 there were two feeders per pen and each had two feeding places for fatteners of 45 kg. Fatteners of 80 kg on farm 3 were fed in a feeding trough of 3.20 m long in each pen. This trough was filled automatically twice daily. Feed was available ad libitum for all pigs on farm 2 and for the 45 kg fatteners on farms 1 and 3. The 80 kg fatteners on the latter farms were fed restrictedly. Water was available ad libitum at all times. Drinkers were positioned in the outside yard, against the wall of the building on farm 1 and 2 (above the slatted floor) and near the scraper on farm 3. On farms 2 and 3, additional drinkers inside the feeders were available Observations and measurements Observations and measurements were carried out for a period of two days on two occasions (in spring and in autumn), on both 45 and 80 kg pigs Behavioural observations Behavioural observations were made using video cameras. For this purpose, two or four cameras were installed for each pen (inside and outside the building). The cameras covered 90% of the area on farm 1 and 100% on farms 2 and 3. Timelapse video recorders on tapes recorded the signal from the cameras. The recording was done on two consecutive days simultaneously for fatteners of 45 and 80 kg on each farm. Data on the excreting behaviour (i.e. the number of urinations and defecations and whether they occurred inside or outside the building), were obtained by analysing the video recordings Composition of urine, faeces and manure On the day after the behavioural observations, representative samples of urine, faeces and manure were taken on each farm. Samples of urine were taken directly from a minimum of five pigs per pen once in the morning and once in the afternoon, using a pan with a long handle. The urine samples of pigs from one compartment were mixed together and one sample of this mixed urine was analysed for total-n, NH 4 + -N, urea-n, ph, dry matter and ash. Samples of faeces, also collected with a long-handled pan, were taken from a minimum of five pigs per pen, once in the morning and once in the afternoon. All faecal samples from the pigs in one pen were mixed well together and a representative sample was taken and analysed for total-n, NH 4 + -N, ph, dry matter and ash. The manure from fatteners was sampled as follows: on farm 1, from straw fouled with faeces and urine inside the pen and from a mixture of urine and faeces on the solid floor of the outside yard; on farm 2, from the manure underneath the slats. This manure not only originated from the pens in this study, but from other pens with fatteners and as well; and on farm 3, from the solid floor of the outside yard, where the scraper ran. The samples per farm were also well mixed and analysed for total-n, NH 4 + -N, ph, dry matter and ash. The urine and faeces were analysed for N, DM and ash N according to AOAC (1990) procedures, and NH 4 + -N was determined using spectrophotometry according to NEN 6472 (NEN, 1983). The ph was measured at room temperature with a Hanna instrument glass electrode (model HI 8417) directly submerged in the excreting product (urine, manure) Outdoor climate The data on air temperature, relative humidity and wind speed were collected from the nearest weather station; only the data for the test days were used. The data covered the period from 9.00 to h. This was the same period of the day during which ammonia emissions were measured Degree of fouling of floor area The degree of fouling of the floor area was assessed visually. The fouled area was defined as the area wetted by urine or by a mixture of urine and faeces. The clean area was defined as a completely dry area. The areas fouled with urine and manure were drawn on a grid diagram of the inside pen and similarly of the paved outside yard. This was done twice on measuring days: just before and immediately after the video observations Ammonia emission Ammonia emission was measured using a ventilated chamber constructed in steel (see Fig. 4) (Aarnink et al., 2002). The base of the box (0.50 m 0.80 m in area) was open; the sides of the box were 0.28 m high (including a rubber edge of 0.03 m height). The box covered a floor area of exactly 0.4 m 2.Two fans on either side of the box (one for incoming air and the other an extractor fan) blew air over this area. The fans ensured an equal atmospheric pressure in the measuring chamber to prevent air leakage. The air stream flowing through the device was sufficiently long to ensure equal distribution of air within the measuring box. A 109 mm diameter rotating vane anemometer (Lambrecht, Göttingen, Germany) was calibrated in a wind tunnel and used to measure the volume of air. The ventilation rate was fixed at 98.5 m 3 h 1. At this ventilation rate the air speed inside the chamber was calculated to be 0.22 m s 1. Ammonia concentrations in the incoming and outgoing air of the chamber were measured with ammonia tubes ( ppm, Kitagawa, Tokyo, Japan), twice at every measurement location and during the period 2 5 min after the chamber was placed on the measuring spot. The chamber was used to measure ammonia emission both inside the building and on the outside paved yard. Ammonia emission at a location was calculated by multiplying the ventilation rate through the chamber with the difference in ammonia concentration between outgoing and ingoing air. A conversion factor of 0.71 was used to convert ammonia concentration from ppm to mg [NH 3 ]m 3 [Air]. To calculate the ammonia emission per m 2 the calculated ammonia emission was divided by the measuring area of the chamber (0.4 m 2 ). The total surface areas of polluted and clean areas were determined. The ammonia measurements were carried out at 9, 10 and 8 locations in each of the two periods in every

5 416 Fig. 4 Chamber for measuring ammonia emission; all dimensions in mm. pen on farms 1, 2 and 3, respectively. The guiding principle was that a similar number of fouled and clean locations in the pen were measured. Ammonia emission was calculated as follows: E t ¼ðA fi E fi þ A ci þ E ci Þ=A ti (1) E o ¼ðA fo E fo þ A co E co Þ=A to (2) E t ¼ E i þ E o, (3) where E i, E o and E t are the ammonia emissions inside, outside and in total in g [NH 3 ]day 1 m 2 ; E fi and E ci are the mean ammonia emissions from fouled and clean areas inside in g [NH 3 ] day 1 m 2 ; E fo and E co are the mean ammonia emissions from fouled and clean areas outside in g [NH 3 ] day 1 m 2 ; A fi and A ci are the fouled and clean areas inside in m 2 ; A fo and A co are the fouled and clean areas outside in m 2 ; and A ti and A to are the total areas inside and outside in m Statistical analyses The means and standard errors of the composition of urine, faeces, manure and feed were calculated for each farm in Excel, for both 45- and 80-kg pigs. Ammonia emission was calculated from the ammonia concentrations of the outgoing and incoming air of the measuring chamber and from the ventilation rate. Data were analysed in a factorial model using the restricted maximum likelihood method (REML) of Genstat Release 7.1. (Genstat 5 Commitee, 1993). Fixed effects were tested by the Chi-square probability test, using the following model: Y ijk ¼ m þ F i þ W j þ M k þðfwþ ij þðfmþ ik þðwmþ jk þ e ijk, where Y ijk is NH 3 emission per m 2 or per pig; m is the overall mean; F is the effect of farm; W is the effect of weight; M is the effect of measuring occasion (spring, autumn); ijk are levels of fixed effects; and e ijk is the error. Each farm was considered representative for its type of organic pig farms in the Netherlands. This is why the effect of farm was taken as a fixed term in the statistical model. First, statistical analysis was done to determine the main effects and their interaction effects on ammonia emission per m 2 and per pig. Then, the effect of location (indoors/outdoors) was added to this model. Finally, the effect of the degree of fouling of area (fouled/not fouled) on ammonia emission was determined, by incorporating it into the model. In all analyses the two-way interactions were calculated. To calculate whether there were between-farm differences in fouled area, as percent of total area, only farm was included as a factor in the model. This analysis was done separately for inside and outside. 3. Results The composition of the excretion products from the fatteners is presented in Table 2. The composition of urine of the farms was similar, but significant between-farm differences in nearly all components of faeces (probability Po0.05) were observed. The faeces of fatteners on farm 3 had significantly higher total N and ammoniacal N (Po0.01) in comparison to

6 417 Table 2 Composition of excretion products from the fattening pigs on three organic farms Component Source Farm a Mean S.E.M. Mean S.E.M. Mean S.E.M. Total N (g kg 1 ) Urine 9.2 a a a 0.72 Faeces 9.1 a a b 0.23 Manure 8.6 a a a 0.32 NH + 4 -N, (g kg 1 ) Faeces 1.0 a a b 0.41 Manure 2.8 a a a 0.67 ph Urine 8.8 a a a 0.65 Faeces 5.9 a b c 0.06 Manure 7.6 a a a 0.09 Dry matter (g kg 1 ) Urine 31.7 a b a 3.23 Faeces a b a 6.97 Manure a a a 5.64 Ash (g kg 1 ) Urine 12.9 a a a 0.73 Faeces 36.6 a b c 1.75 Manure 41.8 a a a 2.25 a Means within a row without a common superscript letter differ significantly (probability Po0.05). Table 3 Mean fouled surface area for fattening pigs inside the building and on the outside yard for the three farms on the measurement days Farm Inside a Outside a m 2 % of total area m 2 % of total area a a b b b b a Means within a column without a common superscript letter differ significantly (probability Po0.01). farms 1 and 2. There was also a between-farm difference in the ph of faeces: farm 3 had the highest ph of faeces (6.38), which differed from farm 2 and 1 (Po0.01). There were no significant differences in the composition of manure from the farms. Table 3 shows the fouled areas inside the building and on outside yard in m 2 fouled and as a percentage of the total area. It is clear that farm 1 had the largest fouled areas inside (13.9% vs. 3.3% on farm 2 and 3.5% on farm 3, Po0.01) as well as outside (79.9% vs. 54.5% on farm 2 and 45.0% on farm 3, Po0.001). In Table 4, ammonia emissions are presented per day per m 2 and per pig. It can be seen that there is a large variation in ammonia emission between farms (Po0.001). In general, farm 1 had a very high level of ammonia emission, particularly on the first measuring occasion (spring), with both 45- and 80-kg fatteners. The same factors affected ammonia emission per m 2, as ammonia emission per pig, because the pigs had a similar available area on each farm. The effect of farm was highly significant (Po0.001). Ammonia emissions were similar for the two weight classes. This was true of farm 1 on both measuring occasions and of farms 2 and 3 on the second occasion. Table 4 shows that season and the interaction between farm and season had a significant influence on ammonia emission (Po0.01). In the second model the location of measurement (inside or outside) was added as a factor. A highly significant effect of location was found on ammonia emission per m 2 and per pig (Po0.001). The results are presented in Table 6. It can be seen that there are clear differences in ammonia emission between farms, especially between farm 1 and the other two farms. On farm 1, the emissions inside were several times higher (7.7 g [NH 3 ] day 1 m 2 ) than on farm 2 (1.9 g [NH 3 ] day 1 m 2 ) and farm 3 (0.0 g [NH 3 ]day 1 m 2 ). The ammonia emissions from outside the yard were clearly higher than from the pens inside. The difference between outside the yard and inside was about a factor of two on farms 1 and 2. The first (spring) ammonia emission measurements on farm 3 indoors were small, calculated as being 0.0 g [NH 3 ]day 1 m 2 and 0.4 g [NH 3 ] pig 1 day 1. From the observations of the behaviour of pigs during the second measuring occasion it was clear that urinations and defecations inside the building were very rare on farm 3. On that farm nearly all the ammonia emissions from fattening pigs came from the outside yard. Finally, the degree of fouling of floor area (clean vs. fouled) was added to the model as a source of variance. The effect on ammonia emission was highly significant (Po0.001). Farm also had a highly significant effect (Po0.001) on the emissions from both the clean and the fouled areas. The effects of measuring occasion and inside/outside area were significant

7 418 Table 4 Effect of farm, weight and season on ammonia emission per day per m 2 and per fattening pig Farm Body weight (kg) Season Emissions Factor Overall effects g [NH 3 ] g [NH 3 ] Probability (P) S.E.D. day 1 m 2 day 1 pig 1 g [NH 3 ] g [NH 3 ] day 1 m 2 day 1 pig Spring Farm Po0.001 Po Autumn Spring Weight n.s. n.s Autumn a 45 Spring Season Po0.01 Po Autumn Spring Farm+weight n.s. n.s Autumn Spring Farm+Season Po0.001 Po Autumn Spring Weight+Season n.s. n.s Autumn a Emission from manure pit not included. (Po0.05). The effect of weight was not significant. On all farms the ammonia emissions from clean areas were much less than from fouled areas, both inside (1.9 vs g [NH 3 ] day 1 m 2 ) as well as outside (2.7 vs g [NH 3 ]day 1 m 2 ). Interestingly, the polluted area inside the building had a higher emission than the polluted area outside in the yard. 4. Discussion The ammonia emitted from agriculture is a conversion product of organic nitrogenous compounds from excreta (urine and faeces) from livestock animals. Its main origin is urea in urine (Aarnink et al., 1993). After deposition on the concrete floor the urea is hydrolysed into NH 3 by the enzyme urease, which is produced by microorganisms present in faeces. This ammonia will subsequently be emitted into the atmosphere at a rate that depends on its concentration and on factors affecting the equilibrium between NH 3 /NH + 4 in solution and between dissolved and gaseous NH 3. Aarnink and Elzing (1998), creating a dynamic model for ammonia volatilisation from buildings for fattening pigs, concluded that the important influencing parameters were the urea concentration of urine and the total ammonium nitrogen (TAN) concentration of manure, ph of urine and manure, urease activity of the floor and floor type, temperature, wind speed and the size of the fouled floor area. Rainfall and cleaning (frequency and efficiency) of the yard might be important additional factors for outdoor yard emission (Misselbrook et al., 2001). Of the total nitrogen ingested by finishing pigs, approximately 50% is excreted in urine and 20% in faeces (Jongbloed & Lenis, 1992; Aarnink, 1997). Both the quantity and the composition of the faeces and urine as well as of the manure are important for ammonia emissions. Very large differences in ammonia emissions were found between the three farms in our study. The much higher ammonia emissions measured on farm 1 are not related to the composition of the excreta because the total N content of urine or the NH 4 -N content of manure on all three farms were similar. The ph of the excretion products was also similar (Table 2). It was expected, because manure production is directly proportional to body weight (Hoeksma et al., 1992), that with increasing weight of the animals the ammonia emissions would also increase. In general, a higher feed intake leads to more nitrogen being excreted in the urine, resulting in larger volumes of urine and larger emitting areas; it may also lead to more concentrated urine, which enhances ammonia concentrations in the slurry. However, the effect of weight of pigs on ammonia emission in this study was found not to be significant. The emission from pens of fatteners of 45 kg body weight was somewhat higher than from pens of fatteners weighing 80 kg. This disagreed with the results of Aarnink et al. (1995), who found that throughout the growing-finishing period the ammonia emissions increased with increasing animal weight. In that study they also recorded relatively low emission from the fatteners during the second half of the fattening period in summer. This might have been due to higher fermentable carbohydrate levels in feed of the 80-kg pigs. Furthermore, animals at 80 kg were feed restricted (farm 1 and 3). A relatively low feed intake in that period, in combination with a high growth rate, may have given a low nitrogen excretion level (Dourmad et al., 1992). The effect of season on ammonia emission, found in our statistical analyses, can most likely be ascribed to differences in ambient temperatures, although the results are not clear in this respect. From both theory and research (Aarnink & Elzing 1998; Elzing & Monteny, 1997) it is known that temperature is an important factor influencing NH 3 emission. On all three farms the measurements were made at an air speed of 0.22 ms 1 over the emitting surface area in the measuring chamber, and so air speed was not a source of variation in our

8 419 Table 5 Outside temperatures, relative humidity of the air and wind speed on the measuring days (from 9.00 to h), according to the nearest weather station Farm Measuring season Temperature (1C) Relative humidity (%) Wind speed (m s 1 ) Mean S.E.M. Mean S.E.M. Mean S.E.M. 1 Spring Autumn Spring Autumn Spring Autumn Outside yard Feeder Drinkers Pen with straw measuring outside foulded area foulded with urine straw point outside clean area inside clean area Fig. 5 Measuring points and fouled areas in pens of 45-kg fattening pigs on farm 1. study. However, by choosing a constant, rather low air speed, ammonia emissions might have been underestimated, especially from outside yards, because the mean wind speed is generally higher (Table 5 ). It should be noted that the emissions from farm 2 did not include emissions from the manure pit. Aarnink et al. (1996) estimated a within-building emission of 18 g [NH 3 ]day 1 m 2 pit area. On farm 2 the pit area per pig was approximately 0.23 m 2, which gives an estimated emission from the manure pit of 4.1 g of ammonia per pig per day, which should be added to the measured emission from the solid floor of the outside yard, to give the total emission from the outside yard. As air velocity is generally higher outside buildings than inside, this 4.1 g of ammonia per pig per day might still be an underestimation of the ammonia emission. The same argument is valid for 80-kg fatteners on farm 3, where a slatted floor is available over the scraper running. According to Elzing et al. (1992), the area of the ammonia source is linearly related to ammonia emission; urination on solid or slatted floors increases emission from the floor. Clear differences between total ammonia emissions on farm 1 and those from farms 2 and 3 were found. On farm 1, there was a large amount of manure in the outside yard and it was distributed all over the yard (Fig. 5) in a thick layer. The much higher rate of ammonia volatilisation on this farm is probably attributable to regular additions of fresh urine from the pigs coming into contact with this layer throughout the day. This is in agreement with Elzing and Swiestra (1993), who found a rapid increase in ammonia emission after sprinkling urine onto fouled slatted floors. This rapid increase is caused by the high activity of enzyme urease on the fouled floors, which hydrolyses urea in the urine into ammoniacal N. In addition, emission from the manure may also increase because of the fresh urine added to the layer (Aarnink et al., 1996). The same applies to the ammonia emission from outside yards reported by Misselbrook et al. (2001); they found that the most influential ammonia emission parameters were the amount of urine and faeces deposited on the yards, urease activity and the efficiency of the removal of urine and faeces. In our study the low NH 3 emissions measured on farms 2 and 3 were probably also attributable to regular removal of the manure. On these farms the manure on the outside yard was cleaned regularly (daily with a scraper on farm 3 and continuously by the slatted floor on farm 2). Occasional deposits of urine and faeces on the solid part of the yard were cleaned every day in the summer and once or twice per week at cooler times of the year. In contrast, on farm 1 the manure was removed every two weeks. This demonstrates the importance of regular cleaning for reduction of ammonia emissions. Monteny and Erisman (1998), who studied ammonia emission from outside yards in cattle, also found that the frequency and efficiency of yard cleaning were additional factors important for emissions from outdoor yards. Airoldi et al. (2000) reported that more frequent manure removal (daily as opposed to weekly or monthly) was effective in reduction of NH 3 emissions. In addition, the design of the floor of the outside yards on farms 2 and 3 may have contributed to the difference in ammonia emissions. On farm 2, the solid part of the outside yard sloped down to the slats at both sides of the yard. On farm 3, the floor of the scraping area sloped down towards the

9 420 Table 6 Least square means of ammonia emissions from fattening pigs inside the building and outside on the yard Farm Inside a Outside a g [NH 3 ]day 1 m 2 g [NH 3 ] pig 1 day 1 g [NH 3 ]day 1 m 2 g [NH 3 ] pig 1 day a 8.0 a 17.6 a 14.5 a b 2.0 b 3.6 b 3.5 b b 0.4 b 5.0 b 4.7 b a Means within a column without a common superscript letter differ significantly (probability Po0.05). centre in such a way that urine could flow to an underground storage pit. Moreover, the floor in the scraped area between pens was perforated. Both types of floors enable urine to be removed rapidly. Thus, farm management can have a clear influence on NH 3 emission and our results are fully in agreement with Vranken et al. (2004). Another factor that appears to influence emission from pig buildings is the pattern of excreting behaviour. When given the choice, the natural behaviour of pigs is to separate their lying and dunging places (Aarnink et al., 1996, van Putten, 2000). In our study, the pigs had a preference to urinate and defecate outside keeping their lying area inside clean. Thus, the polluted area outside was larger than that inside. Because ammonia emission is positively related to the fouled area (Aarnink et al., 1996), this also helps explain the effect of indoor/outdoor area on ammonia emission. On farm 3, the pigs urinated and defecated solely in the area cleaned by the scraper. Only the outermost section against the fence on farm 3 was fouled. On farm 2, we observed that most of the urinations and defecations were on the slatted floor. On some hot days in autumn some excretions occurred on the solid part of the floor. At high ambient temperatures, pigs prefer to lie on a cool surface, mostly the slatted area, and so they dung on the warmer surface: the solid floor. The high indoor ammonia emission from farm 1 may be due to the higher number of pigs per group: compared with pigs per group on farm 2 and pigs per group on farm 3. Farm 1 also had more pigs per feeding place: pigs, compared with 5 7 pigs on farms 2 and 3 (for 45 kg pigs). The provision of dry feed on farm 1, together with the long distance to drinkers in the outside yard, meant that not all the pigs synchronised their active and rest periods. The pigs were also active for more hours per day. This might have contributed to the higher fouling rate of the straw inside. Another reason for the higher fouling rate of the straw inside on farm 1 could be that pigs brought manure inside on their fouled legs. The straw fouled with manure became odorous, and so perhaps the pigs perceived the area as a dunging place. From the drawings of fouled areas it was confirmed that for both the 45- and 80-kg pigs, the pens were mainly fouled near the entrance. The 45-kg pigs also had other fouled spots in the pen, probably because there was more area per pig (Table 1). When they were young, the pigs separated the inside area into a lying area and a dunging area. On farms 2 and 3 the pigs perceived the entire inside area as a lying place. The effect of fouling with urine on ammonia emission in this study is very clear. Furthermore, a fouled area inside caused higher emissions per m 2 than a fouled area outside (13.3 g[nh 3 ] day 1 m 2 vs g[nh 3 ] day 1 m 2 ). These results correspond to the results of Jeppsson (1998) from deep litter beds for conventionally growing pigs (average 10 g[nh 3 ] day 1 m 2 ammonia), and to the results of von Wachenfelt (2002) and von Wachenfelt and Jeppsson (2006) from outside yards for organic pig production (average 9 12 g [NH 3 ]day 1 m 2 ammonia). In this system a lot of straw is used inside the buildings to improve animal welfare. This can lead to a buildup of dung and urine which can continue to emit ammonia for a longer period of time than if the dung had dropped through a slatted floor (Sommer et al., 2006), as it is in conventional systems. Fouled straw probably has a larger emitting area than a paved yard. Moreover, the temperature inside the building was generally higher than the temperature outside and fouled straw also generates heat by the composting process. In this study the area fouled with urine was monitored at different times during the day ( h). Although we measured ammonia emissions on numerous spots on the different farms, we may have introduced a systematic error in the emission level by measuring only during daytime. It should be noted that our measurements were carried out to compare the ammonia emissions from organic pigs related to design and management of the farm and how pigs use indoor and outdoor areas rather than to establish estimates over a long periods. 5. Conclusions Ammonia emissions from pens for fattening pigs differed greatly between the organic farms studied (probability Po0.001). The effects of measuring season (spring vs. autumn), inside vs. outside area, and degree of fouled floor area (clean vs. fouled) on ammonia emissions were highly significant (Po0.001). The farms with slats and scraper had significantly lower emissions than the farm with manual removal of manure from a solid floor. The main factors influencing ammonia emission appear to be manure removal, and the management system, as well the design of the buildings and frequency of cleaning of the yard. Regular cleaning of the outside yard seems very important to reduce ammonia emission. The excreting behaviour of pigs affected the ammonia emissions inside the building. Possible ways to influence this behaviour in order to reduce emissions are to ensure a proper

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