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Ammonia volatilization from artificial dung and urine patches measured by the equilibrium concentration technique (JTI method)
ARTICLE IN PRESS
Atmospheric Environment 40 (2006) 5137–5145 www.elsevier.com/locate/atmosenv
Ammonia volatilization from artificial dung and urine patches measured by the equilibrium concentration technique (JTI method) K. Saarija¨rvia,, P.K. Mattilab, P. Virkaja¨rvia a
Agrifood Research Finland, Maaninka, Halolantie 31, 71750 Maaninka, Finland b Agrifood Research Finland, Soil and Environment, 31600 Jokioinen, Finland
Received 18 November 2005; received in revised form 16 March 2006; accepted 25 March 2006
Abstract The aim of this study was to investigate the dynamics of ammonia (NH3) volatilization from intensively managed pastures on a soil type typical of the dairy production area in Finland and to clarify the effect of rainfall on NH3 volatilization. The study included two experiments. In Experiment 1 the total amount of NH3–N emitted was calculated based on the annual surface coverage of dung (4%) and urine (17%). The application rate of total N in the simulated dung and urine patches was approximately 47 g N m2 and 113 g N m2, respectively. In Experiment 1 the general level of NH3 emissions from the urine patches was high and the peak volatilization rate was 0.54 g NH3–N m2 h1. As expected, emissions from the dung pats were clearly lower with a maximum rate of 0.10 g NH3–N m2 h1. The total emission calculated for the whole pasture area (stocking rate four cows ha1 y1, urine coverage 17% and dung coverage 4%) was 16.1 kg NH3–N ha1. Approximately 96% of the total emission originated from urine. In Experiment 2 we measured the emissions from urine only and the treatments on the urine patches were: (1) no irrigation, (2) 5+5 mm and (3) 20 mm irrigation. The peak emission rates were 0.13, 0.09 and 0.04 g NH3–N m2 h1 and the total emissions were 6.9, 3.0 and 1.7 kg NH3–N ha1, for treatments (1), (2) and (3), respectively. In both measurements over 80% of the total emission occurred during the first 48 h and there was a clear diurnal rhythm. Increasing rainfall markedly decreased NH3 emission. Volatilization was highest with dry and warm soil. The JTI method appeared to be suitable for measuring NH3 volatilization in this kind of experiment. According to our results, the importance of pastures as a source of NH3 emission in Finland is minor. r 2006 Elsevier Ltd. All rights reserved. Keywords: Ammonia; Nitrogen; Pasture; Gaseous emissions; Dairy cattle; Finland
1. Introduction Corresponding author. Tel.: +358 17 2644 821;
fax: +358 17 2644 851. E-mail addresses: kirsi.saarijarvi@mtt.fi (K. Saarija¨rvi), pasi.mattila@helsinki.fi (P.K. Mattila), perttu.virkajarvi@mtt.fi (P. Virkaja¨rvi). 1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.03.052
Ammonia (NH3) volatilization is a major pathway of nitrogen (N) emissions from agriculture. In 1995, the estimated amount of NH3 emissions in Finland was 35 000 t. Up to 90% of the total amount originates from agriculture, mainly from
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slurry and manure spreading (Gro¨nroos et al., 1998). The risk of NH3 volatilization is greatest when slurry is broadcast on the soil surface during warm and windy weather. According to previous studies, over 20% of the total N from surfacespread cattle slurry may be lost by volatilization (Mattila and Joki-Tokola, 2003). Excreta is also deposited on the soil surface in grazing. In intensive grazing, the total amount of N deposited in dung and urine may be considerable, since about 60–80% of the N ingested by the cows is returned to the pasture in dung and urine (Haynes and Williams, 1993). NH3 emission is dependent on the wind speed, air temperature and soil properties such as pH, moisture, texture, cation exchange capacity (CEC) and temperature, (Bolan et al., 2004). Because of the large variation in NH3 emission caused by climatic and soil conditions, further local research is needed in order to make accurate estimates of regional emissions (Bolan et al., 2004, Bussink, 1996). In particular, none of the previous NH3 emission studies provides valid information on pastures in northern latitudes, as the typical CEC is low (o20 cmol kg1) and the amount of rainfall is usually fairly high (4300 mm) during summers. There are several methods available for measuring NH3 emissions. The most commonly used in previous studies are the mass balance, wind tunnel and micrometeorological methods (Ross and Jarvis, 2001, Bussink, 1996). In this study we used the micrometeorological chamber technique (JTI method; Svensson, 1994). Earlier, the JTI method was used for measuring NH3 volatilization from evenly spread manure or fertilizer (Mattila and JokiTokola, 2003; Rodhe and Rammer, 2002; Misselbrook and Hansen, 2001). The results obtained from comparison of the JTI and integrated horizontal flux (IHF) methods were fairly uniform, even though it was concluded that the JTI method could overestimate emissions higher than 400 g N ha1 h1 (Misselbrook and Hansen, 2001). As the method should be suitable for measuring volatilization from small plots, we studied NH3
emissions from simulated average-sized dung and urine patches. The aim of this study was (1) to investigate the dynamics of NH3 volatilization from intensively managed pastures on a soil type typical of the dairy production area in Finland and (2) to clarify the effect of rainfall on NH3 volatilization. 2. Material and methods 2.1. Experimental site and design The study was carried out during the summers of 2002 and 2003 at Agrifood Research Finland (MTT), North Savo Research Station, Maaninka (631100 N, 271180 E). The soil texture at a depth of 0–10 cm was mainly fine sand (Table 1). The soil moisture content was measured by time domain reflectometry (TDR, Delta-T devices, Cambridge, UK). The soil and air temperatures and the air moisture content were measured by Hobo H8 (Onset Computer Corporation, Boume, MA, USA) and wind speed by a cup anemometer (Wilh. Lambrecht GmbH, Go¨ttingen, Germany) at a height of 2 m. In the experiments the total amount of NH3–N emitted was calculated based on the previously determined annual percentage surface coverage of dung and urine (4% and 17% of the pasture per year, respectively) at the average intensive grazing pressure (herbage allowance 25 kg dry matter (DM) cow1 d1, average stocking rate four cows ha1 y1). The average mass and area of urination and defecation were measured earlier (2.37 kg and 0.35 m2 for urine and 2.47 kg and 0.08 m2 for dung) and the data were used in the experiments. Total N, NH4–N, DM concentrations and pH values of the urine and dung used in Experiment 1 (Exp 1) and Experiment 2 (Exp 2) are presented in Table 2. The application rate of total N in the simulated dung and urine patches was approximately 47 g N m2 and 113 g N m2, respectively. Fresh urine and dung were collected directly from grazing dairy cows in the morning on the first day of each measurement. Samples were taken for the
Table 1 Soil properties (0–10 cm) at the experimental sites
Exp 1 Exp 2
0.002 mm (%)
0.002–0.02 mm (%)
0.02–0.2 mm (%)
0.2 mm (%)
pH
CEC (cmol kg1)
7.7 11.6
11.9 20.7
73.5 49.9
6.9 17.8
6.13 5.86
4.0 3.4
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Table 2 Total N, NH4–N, urea and DM concentrations and pH values of the urine and dung used in Experiments 1 and 2
Experiment 1 Measurement Measurement Measurement Measurement
Total N (g l1)
NH4–N (g l1) fresh urine
NH4–N (g l1) after 48 h
DM (%)
pH
1 2 1 2
Dung Dung Urine Urine
3.8 3.2 7.4 7.5
0.24 0.18 0.04 0.06
nd nd 5.8 5.9
11.9 10.0 5.4 4.8
6.6 6.8 8.5 8.3
Experiment 2 Measurement 1 Measurement 2
Urine Urine
7.5 8.3
0.05 0.06
5.8 6.5
5.1 5.4
8.3 8.4
analysis of total N (Kjeldahl N), ammoniacal N, DM content and pH by the methods used by Kemppainen (1989) (Table 2). The analysis of ammoniacal N included extraction with a solution containing HCl and CaCl2 and subsequent determination of ammonium by distillation of the extract. Before the analysis, samples were stored at 4 1C, except for one urine sample that was stored at room temperature for 48 h to allow the urea N to be converted to the NH4 form. NH3 volatilization was measured with the equilibrium concentration technique (JTI method; Svensson, 1994). The method employs passive diffusional NH3 samplers which are placed at the soil surface both in ambient air and inside chambers that have a constant ventilation rate. The method gives the amount of volatilized NH3 per area and unit of time in the weather conditions prevailing in the ambient air during the measurement. An ambient air sampler holder was placed in the middle of each artificial urine or dung patch. Urine or dung was also applied to the whole area covered by each chamber at the same rate as to the artificial patch. Each replicate consisted of one patch for ambient air measurement and one chamber. The thickness of the laminar boundary layer under the chambers (Llbl,ch) was measured by exposing L-type samplers (Svensson, 1994) in one chamber of each treatment. To estimate the total amount of volatilized N, NH3, the emission between measurement periods was interpolated taking into account the temperature and wind speed during the intervals (Malgeryd, 1996). In Exp 1, measurements were made also at night, but these results may be affected by the condensation of water inside the chambers. Therefore, the results from night measurements were not used when calculating the total NH3–N emission.
Exp 1 comprised two measurements in 2002 (Table 3). The first one lasted for 5 days (June 17–21) and the second was prolonged to 8 days (August 26–September 2) based on the results from the first measurement (Table 4). The experimental field was a second-year timothy-meadow fescue sward. Two hours before the experiment started the grass was cut to 10 cm which is the recommended post-grazing sward height in Finland (Virkaja¨rvi et al., 2002). The whole experimental area was fertilized on May 14 with 100 kg ha1 N, 48% of which was in the form of NO3–N and the rest in the form of NH4–N. The area for the second measurement was also cut and fertilized on June 18 with 100 kg N ha1 and then cut again on August 26. There were four replicates for both urine and dung and one background patch. Each measurement period lasted for 90 min, except when the temperature was below 16 1C when the duration was extended to 120 min. Exp 2 comprised two measurements in 2003, the first on June 24–July 2 and the second on August 18–26. Both measurements lasted for 8 days (Table 3). Exp 2 was performed on a first-year timothymeadow fescue sward cut to 10 cm 2 h before the experiment started. The whole area was fertilized on May 20 with 88 kg ha1 N. The area for the second measurement was also cut and fertilized on June 18 with 80 kg ha1 N and on July 31 with 52 kg N and cut again on August 18. In all fertilization applications, 48% of the N was in the form of NO3–N and the rest in the form of NH4–N. The treatments in Exp 2 were: (1) no irrigation, (2) 5+5 mm irrigation and (3) 20 mm irrigation. The first irrigation in treatments 2 (5 mm) and 3 (20 mm) was applied between periods 1 and 2 and the second irrigation for treatment 2 was applied
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Table 3 Measured treatments and timing of measurement periods in Experiment 1 (U ¼ urine, D ¼ dung) and in Experiment 2 Period
N
Experiment 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 4 4 4 4 4 4 4 4 4 4 4 4 4 4
Experiment 1 2 3 4 5 6 7 8
2 3 3 3 3 3 3 3 3
Date
Time
Hour
17.6.
14:00 16:00 20:00 2:00 9:30 15:00 20:00 2:00 9:30 15:00 20:00 9:30 15:00 15:00
1 3 7 13 21 26 31 37 45 50 55 69 74 98
12:00 17:00 10:30 15:30 15:00 15:00 12:00 18:00
1 6 24 29 52 76 121 199
18.6.
19.6.
20.6. 21.6. 24.6. 25.6. 26.6. 27.6. 29.6. 2.7.
Measured treatment
Date
Time
Hour
Measured treatment
U U U U U U U U U U U U U U
26.8.
14:00 17:00 20:00 2:00 9:30 15:00 20:00 2:00 9:30 15:00 20:00 15:00 14:00 15:00
1 4 7 13 21 26 31 37 45 50 55 74 97 122
U U U U U U U U U U U U U U
13:00 17:00 10:00 14:00 13:00 13:00 13:30 11:30
1 5 23 27 50 74 122 192
20 and 5 mma
D
27.8. D 28.8. D 29.8. 31.8. 2.9.
D
20 and 5 mma
18.8.
5 mmb
19.8. 20.8. 21.8. 23.8. 26.8.
D
D
D
D
5 mmb
Timing of the irrigation treatments and measurement periods in Experiment 2. Only urine was applied in Exp 2. a 20 mm and first part of the 5+5 mm irrigation was given between measurements 1 and 2. b Second part of the 5+5 mm irrigation was given between measurements 3 and 4.
Table 4 Average values of applied N and NH3 emissions from the dung pats and the urine patches in Experiment 1 and from the 0, 5+5 and 20 mm irrigated urine patches in Experiment 2 Experiment 1
Experiment 2
Urine
SE
Dung
SE
0 mm
SE
5+5 mm
SE
20 mm
SE
Measurement 1 Applied total N g Applied as urea and NH4–N g Lost as NH3–N g NH3–N volatilization % of total N
17.5 13.7 3.2 18.4
– – 0.48 2.76
9.3 0.6 0.1 1.2
– – 0.01 0.09
16.2 12.9 1.3 8.0
– – 0.34 2.09
16.2 12.9 0.6 3.7
– – 0.1 0.62
16.2 12.9 0.4 2.2
– – 0.06 0.37
Measurement 2 Applied total N g Applied as urea and NH4–N g Lost as NH3–N g NH3–N volatilization % of total N
17.8 13.9 3.2 17.8
0.73 4.09
7.8 0.4 0.1 1.4
– – 0.01 0.18
19.6 15.7 1.5 9.5
– – 0.37 2.29
19.6 15.7 1 6
– – 0.16 0.97
19.6 15.7 0.4 2.5
– – 0.07 0.44
SE ¼ standard error of mean.
(5 mm) between periods 3 and 4. The duration of each measurement period was 90 min. There were three replicates of the irrigation treatments and a background patch.
3. Results The samplers exposed in ambient air and the Ctype samplers of the chambers were not over-
ARTICLE IN PRESS exposed and, therefore, no results were lost due to overexposure. The L-samplers exposed under the chambers were supersaturated during periods with high NH3 volatilization, but useful results were obtained for the calculation of Llbl,ch from about half of the periods (data not shown).
NH3-N g m-2 h-1
K. Saarija¨rvi et al. / Atmospheric Environment 40 (2006) 5137–5145
3.1. Experiment 1
Urine Dung
Air temp C
Ground temp C
Wind speed m/s
25 C/m/s
The general level of NH3 emissions from the urine patches was high. The highest volatilization rates were 0.34 and 0.54 g NH3–N m2 h1 in June and August, respectively. As expected, emissions from the dung pats were clearly lower with a maximum rate of 0.10 g NH3–N m2 h1. The volatilization followed the typical pattern, being high in the afternoon and low at night. The total amount of volatilized NH3–N from the urine patches was over five times greater than from the dung pats. In June, the NH3 volatilization especially from the dung pats remained appreciable between 48 and 96 h after application. Therefore, measurement in August was prolonged to 168 h. However, the volatilization rate remained low (o0.7 g NH3–N m2 h1) between 31 and 168 h after the application. The daytime temperatures were fairly similar in June and August (means 19.9 and 18.2 1C, respectively, Fig. 1). At night the temperature was slightly higher in June than in August (means 13.6 and 11.7 1C, respectively). The relative humidity followed a diurnal pattern with a typical daytime minimum of 32–50% and a night-time maximum near 100%. In June the wind speed was typically between 0 and 2 m s1 but increased between 48 and 80 h to a maximum of 8.3 m s1. In August the wind speed was between 0 and 4.9 m s1. The soil was extremely dry in the beginning of both measurements. The TDR probe showed soil moistures of 0.104 m3 m3 and 0.090 m3 m3 for June and August, respectively. The precipitation during measurement 1 was 4.5 mm, of which 4.1 mm was on day 1 between 3 and 7 h after application. During measurement 2 the total precipitation was 22.9 mm, of which 1.8 mm occurred 50 h after application 6.3 mm between 74 and 97 h after application 13.2 mm between 97 and 122 h after application. The soil temperature range in depth of 10 cm in June was 21.0–14.1 1C (mean 17.5 1C). Data from August are not available because of equipment failure.
0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 30
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20 15 10 5 0 0
24
48 72 Hours after application
96
Fig. 1. NH3 volatilization from artificial dung and urine patches, air temperature and wind speed during measurement 1 in Experiment 1 in June 2002. Vertical bars represent SE.
3.2. Experiment 2 The NH3 volatilization from the 0 mm irrigation urine patches was lower than in Exp 1. The emission peaks were 0.09 and 0.13 g NH3–N m2 h1 in June and August, respectively (June; Fig. 2). The peak emission from the 5+5 mm treatment in June was 0.071 g NH3–N m2 h1 but, in August the peak value was the same as from the 0 mm treatment. The peak values from the 20 mm treatment were 0.04 and 0.03 g NH3–N m2 h1 in June and August, respectively. The total NH3–N emission from the 0 mm treatment was less than half that of the previous year (Table 4). However, without precipitation the proportion of volatilized NH3–N of the total N applied was almost twice that from the 5+5 mm treatment and four times greater than from the 20 mm treatment. Daytime temperatures in June were a little higher than in August (means 18.1 and 16.6 1C, respectively). The night-time temperatures were similar (means 12.1 and 12.6 1C, respectively). The relative humidity followed a diurnal pattern with a typical daytime minimum of 36–60% and night-time maximum near 100%. In June the wind speed exceeded 3 m s1 (peak 3.7 m s1) only twice briefly during the first period. The rest of the measurement
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20 mm irrigation and first part of the 5 + 5 mm irrigation
0.18
0 mm
NH3-N g m-2h-1
0.16
5 + 5 mm
0.14
Second part of the 5 + 5 mm irrigation
0.12
20 mm
0.10 0.08 0.06 0.04 0.02 0.00 30 Air temp C
Ground temp C
Wind speed m/s
25
C/m/s
20 15 10 5 0 0
24
48 72 Hours after application
96
120
Fig. 2. NH3 volatilization from artificial urine patches, air and ground temperature and wind speed during measurement 1 in Experiment 2 in June 2003. Vertical bars represent SE.
periods in June and throughout measurement periods in August the wind speed remained below 3 m s1. The soil moisture was high at the beginning of both measurements with TDR showing soil moistures of 0.345 m3 m3 and 0.347 m3 m3 for June and August, respectively. The precipitation in June was 1.4 mm and in August 8.6 mm. The soil remained moist throughout the measurements. The soil temperature range at a depth of 10 cm was 17.3–11.5 1C (mean 14.4 1C) and 16.9–12.2 1C (mean 14.9 1C) in June and August, respectively. 4. Discussion The JTI method appeared to be applicable to the kind of measurement carried out here. The edge effect certainly lowers the NH3 concentration in the ambient air above a urine or dung patch, but this corresponds to the actual situation with genuine patches and should not bias the results. However, the NH3 concentration in the ambient air over a pasture with many urine and dung patches may be somewhat higher than in an experiment with only a few patches.
4.1. Effect of treatments Even though the peak emission rates found during the first day of the measurements were high, the proportional emissions over the entire measurements were on a moderate level (1–17% of applied N) compared with the large variation in the literature (3–52%) (Sherlock and Goh, 1984; Ryden et al., 1987; Petersen et al., 1998; Whitehead and Raistrick, 1993). The NH3 emission from dung was less than 5% of the total N applied. This result is in line with other studies (Petersen et al., 1998). The slight increase 74 h after application in June in Exp 1 was probably caused by high wind speed and a large number of insect holes on the surface crust of the dung pats. The peak NH3 emission rates from urine in Exp 1 were high (Figs. 1 and 2) compared with the results of Misselbrook and Hansen (2001) who measured 898 and 905 g NH3–N ha1 h1 by the JTI method from granulated urea and band-spread cattle slurry, respectively, applied to grassland. However, since they used low N application rates (138 kg N ha1 urea, 50 kg NH4–N ha1 slurry), the
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NH3 volatilization is in fairly good agreement with our experiment. Mattila and Joki-Tokola (2003) measured, on average, 3700 and 2000 g NH3–N ha1 h1 by the JTI method from broadcast and band-spread cattle slurry, respectively, during the day of application to ley. These figures are well in line with ours. The relative N loss from urine is lower than that from slurry obviously because of the greater infiltration of urine into the soil. Irrigation of 5+5 mm reduced the NH3 volatilization by 46% and 20 mm by 75% (Fig. 2). Heavy rainfall is known to diminish NH3 volatilization (Bussink, 1996; Whitehead and Raistrick, 1991). However, light rainfall (o5 mm) has increased NH3 volatilization (Bussink, 1996). In our case, the first irrigation of 5 mm given immediately after the first measuring period (1.5 h after application) diminished the NH3 volatilization by ca. 20% compared to the no irrigation treatment. The major part of the decrease occurred after the second 5 mm irrigation applied 25.5 h after application (between periods 3 and 4). In Exp 1, the total emission from the pasture was 16.1 kg NH3–N ha1 when the relative coverage percentages of dung and urine were taken into account. Approximately 96% of the total emission originated from urine. In Exp 2, multiplying the amount of NH3–N volatilized from the urine patches (mean of measurements 1 and 2) by the coverage percentage of urine on pasture gave emissions of 6.9, 3.0 and 1.7 kg NH3–N ha1 for the irrigation treatments of 0, 5+5 and 20 mm, respectively. In both experiments, the calculated total emission was comparable with Bussink (1996) who measured 9.1 kg total NH3–N emission from pasture fertilized with 250 kg N ha1. In our study we did not measure the NH3–N volatilization from fertilizers, and this probably lowers the total emission from the pasture. However, according to the literature, the amount volatilized from granulated fertilizers is small (Sommer et al., 2004), and thus our results should give a relatively accurate estimate of the total NH3–N emission. 4.2. Factors affecting NH3 emission NH3 emission is dependent on the soil pH, moisture, texture, (CEC) and temperature, as well as on the wind speed and air temperature (Bolan et al., 2004). The N concentration and hippuric acid content of urine are also important factors (Petersen et al., 1998).
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In both our experiments, measurements from June and August were very similar, but there was a large difference between the experiments in respect of peak concentrations and the total amount of NH3 volatilized. Overall, the level of volatilization in Exp 2 was only half that of Exp 1. The pH value of the soil in Exp 1 was slightly higher than in Exp 2, which could partly explain the higher emission rate (Table 1). The measured CEC value of the soil was so low in both experimental areas (o10 cmol kg1) that, according to Whitehead and Raistrick (1993), it could not have affected the emission rates. As the weather conditions (air temperature and rainfall) were also comparable during the experimental years, the reason for the difference in the amount of volatilization could be in the soil parameters. This is also supported by the fact that the NH3 concentration inside the chamber, where the influence of the varying wind conditions on the ambient air is minimal, was over three times higher during day 1 in Exp 1 than in Exp 2 (data not presented). Soil moisture and temperature are known to influence the NH3 emission from urine (e.g. Whitehead and Raistrick, 1991; Haynes and Williams, 1993). The greatest difference between Exp 1 and 2 occurred in the soil moisture content at the beginning of the experiments. In Exp 1 the soil was dry, even hydrophobic (soil volumetric water content ca. 10%) when applying the treatments. In Exp 2, on the contrary, the soil volumetric water content at the beginning of the measurements (ca. 35%) exceeded the water holding capacity ca. y 30% at 0.1 MPa measured from the same area by Pietola et al. (2004). Previously wet soil has increased volatilization compared to dry soil (Whitehead and Raistrick, 1991), but in our case the outcome was the opposite. We suggest that this was partly caused by hydrophobic soil conditions, which could have caused the urine to spread on larger surface area in Exp 1 than in Exp 2 and partly by soil temperature which was on average over 3 1C and occasionally over 5 1C higher in Exp 1 than in Exp 2 (Figs. 1 and 2). The importance of soil temperature for NH3 volatilization is supported by van der Putten and Ketelaars (1997). According to Rachhpal-Singh and Nye (1986a,b), the increase in volatilization with increasing temperatures is partly caused by increased urease activity, partly by a greater proportion of the ammoniacal N being present as NH3 gas and partly by faster
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diffusion. For example, urea hydrolysis in soil increased with increasing temperatures from 10 to 40 1C (Vlek and Carter, 1983) while the volatilization increased with increasing temperature up to 20 1C (Whitehead and Raistrick, 1991). Studies made in stable laboratory conditions do not take into account the diurnal temperature rhythm that markedly lowers the temperature of wet soil during the nights and also slows down the warming of the soil during the days. Consequently, a high daytime air temperature is an inadequate descriptor of the soil temperature when the soil volumetric water content is high, as it was in our case. In conclusion, the most important reason for the higher NH3 volatilization in Exp 1 was the combination of dry soil and, consequently, high soil temperatures during the afternoons. The N concentration of the urine was a little higher than average level based on the literature (Bussink, 1996; Petersen et al., 1998) and N concentration of total diurnal urine (6.96 g l1) collected from six cows fed pasture grass indoors on three separate occasions (Sairanen, unpublished). As the difference in N concentration between the years was small, the urine N concentration probably had a minor effect on NH3 volatilization. The hippuric acid concentration of the urine was not measured.
between 20% and 60% of the emitted NH3 is deposited within 2 m. Based on these results, the volatilization of NH3 from pasture is of minor importance and grazing needs little attention as a source of NH3 emissions in Finland.
4.3. The importance of the results
We wish to thank Heikki Riisio¨, M.Sc., for his excellent assistance in the field work and Dr. Helvi Heinonen-Tanski for her valuable comments on the manuscript. This work was financially supported by the Finnish Cultural Foundation and the Finnish Ministry of Agriculture and Forestry.
Compared with our results, some of the previous national NH3 emission estimates of Finnish pastures are overestimates. Kera¨nen and Niskanen (1987) use the results of Buijsman et al. (1987) and estimate that 5% of the dung N and 40% of the urine N are volatilized during grazing. Pipatti (1990) gives a figure of 6.5 kg NH3–N y1 cow1 during the grazing season, while our result 16.1 kg NH3–N ha1 transforms to 4.0 kg NH3–N y1 cow1 when divided by average stocking rate of four cows ha1 y1. As the weather conditions during the Exp 2 were more comparable to the average Finnish summer than in the Exp 1, the actual total volatilization is probably even lower than that. The pasture area in Finland is approximately 110 000 ha. The annual NH3 emission from pastures calculated from our results is 710–1570 t. This is only 2.3–5% of the total NH3 emission caused by agricultural activities (Gro¨nroos et al., 1998). Furthermore, according to Ross and Jarvis (2001),
5. Conclusions 1. The dynamics of NH3 volatilization were well in line with previous research. Over 80% of the total emission occurred during the first 48 h and a clear diurnal rhythm of volatilization was observed. 2. Increasing rainfall markedly decreased NH3 emission. 3. The most important factor explaining the differences in volatilization in this experiment was the combination of soil moisture content and soil temperature. Volatilization was highest with dry and warm soil. 4. The JTI method appeared to be applicable for measuring NH3 volatilization from simulated urine and dung patches. 5. According to our results, the importance of pastures as a source of NH3 emission in Finland is minor and has been overestimated previously. Acknowledgments
References Bolan, N.S., Saggar, S., Luo, J., Bhandral, R., Singh, J., 2004. Gaseous emissions of nitrogen from grazed pastures: processes, measurements and modelling, environmental implications and mitigation. Advances in Agronomy 84, 37–120. Buijsman, E.D., Maas, H.F., Asman, W.A., 1987. Anthropogenic NH3 emissions in Europe. Atmospheric Environment 21, 1009–1022. Bussink, D.W., 1996. Ammonia volatilization from intensively managed dairy pastures. Thesis Landbouwuniversiteit Wageningen, 177 pp. Gro¨nroos, J., Nikander, A., Syri, S., Rekolainen, S., Ekqvist, M., 1998. Maatalouden ammoniakkipa¨a¨sto¨t. (Ammonia emissions from agriculture) Suomen ympa¨risto¨ 206, 68 pp (in Finnish).
ARTICLE IN PRESS K. Saarija¨rvi et al. / Atmospheric Environment 40 (2006) 5137–5145 Haynes, R.J., Williams, P.H., 1993. Nutrient cycling and soil fertility in the grazed pasture ecosystem. Advances in Agriculture 49, 199. Kemppainen, E., 1989. Nutrient content and fertilizer value of livestock manure with special reference to cow manure. Annales Agriculturae Fenniae 28, 163–284. Kera¨nen, S., Niskanen, R., 1987. Typpilannoituksen vaikutus happamoitumiseen Suomessa. Kirjallisuusselvitys. Ympa¨risto¨ministerio¨. Ympa¨risto¨n- ja luonnonsuojeluosasto. Sarja D 30/1987, 64pp (in Finnish, summary in English). Malgeryd, J. 1996. A˚tga¨rder fo¨r att minska ammoniakemissionerna vid spridning av stallgo¨dsel (Measures to reduce ammonia emissions following application of animal manure). JTI-rapport, Lantbruk and Industri nr 229, Swedish Institute of Agricultural Engineering, Uppsala (in Swedish, summary in English). Mattila, P.K., Joki-Tokola, E., 2003. Effect of treatment and application technique of cattle slurry on its utilization by ley: I. Slurry properties and ammonia volatilization. Nutrient Cycling in Agroecosystems 65, 221–230. Misselbrook, T.H., Hansen, M.N., 2001. Field evaluation of the equilibrium concentration technique (JTI method) for measuring ammonia emission from land spread manure or fertilizer. Atmospheric Environment 35, 3761–3768. Petersen, S.O., Sommer, S.G., Aas, O., Søegaard, K., 1998. Ammonia losses from urine and dung of grazing cattle: effect on N intake. Atmospheric Environment 32, 295–300. Pietola, L., Horn, R., Yli-Halla, M., 2004. Effects of trampling by cattle on the hydraulic and mechanical properties of soil. Soil and Tillage Research 82 (1), 99–108. Pipatti, R., 1990. Ammoniakkipa¨a¨sto¨t ja –laskeuma Suomessa. Valtion teknillinen tutkimuskeskus. Tutkimuksia 711, Espoo, 41pp. Rachhpal-Singh, Nye, P.H., 1986a. A model of ammonia volatilization from applied urea. I. Development of the model. Journal of Soil Science 35, 519–527. Rachhpal-Singh, Nye, P.H., 1986b. A model of ammonia volatilization from applied urea. III. Sensitivity analysis, mechanisms and applications. Development of the model. Journal of Soil Science 37, 31–40.
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Rodhe, L., Rammer, C., 2002. Application of slurry to ley by band spreading and injection methods. Biosystems Engineering 83 (1), 107–118. Ross, C.A., Jarvis, S.C., 2001. Measurement of emission and deposition patterns of ammonia from urine in grass swards. Atmospheric Environment 35, 867–875. Ryden, J.C., Whitehead, D.C., Lockyer, D.R., Thompson, R.B., Skinner, J.H., Garwood, E.A., 1987. Ammonia emission from grassland and livestock production systems in the UK. Environmental Pollution 48, 173–184. Sherlock, R.R., Goh, K.M., 1984. Dynamics of ammonia volatilization from simulated patches and aqueous urea applied to pasture. III. Field verification of a simplified model. Fertilizer Research 6, 23–36. Sommer, S.G., Schjoerring, J.K., Denmead, O.T., 2004. Ammonia emission from mineral fertilizers and fertilized crops. Advances in Agronomy 82, 557–622. Svensson, L., 1994. A new dynamic chamber technique for measuring ammonia emissions from land-spread manure and fertilizers. Acta Agriculturae Scandinavica. Section B. Soil and Plant Science 44, 35–46. van der Putten, A.H.J., Ketelaars, J.J.M.H., 1997. Ammonia volatilization from dairy farms: experiments and model, In: Jarvis, S.C., Pain, B.F. (Eds.), Gaseous Nitrogen Emissions from Grasslands. 1997, CAB International, Wallingford, 452pp. Vlek, P.L.G., Carter, M.F., 1983. The effects of soil environment and fertilizer modifications on the rate of urea hydrolysis. Soil Science 136, 56–63. Virkaja¨rvi, P., Sairanen, A., Nousiainen, J.I., Khalili, H., 2002. Effect of herbage allowance on pasture utilization, regrowth and milk yield of dairy cows in early, mid and late season. Animal Feed Science and Technology 97, 23–40. Whitehead, D.C., Raistrick, N., 1991. Effects of some environmental factors on ammonia volatilization from simulated livestock urine applied to soil. Biology and Fertility of Soils 11, 279–284. Whitehead, D.C., Raistrick, N., 1993. The volatilization of ammonia from cattle urine applied to soil as influenced by soil properties. Plant and Soil 148, 43–51.
Atmospheric Environment 40 (2006) 5137–5145 www.elsevier.com/locate/atmosenv
Ammonia volatilization from artificial dung and urine patches measured by the equilibrium concentration technique (JTI method) K. Saarija¨rvia,, P.K. Mattilab, P. Virkaja¨rvia a
Agrifood Research Finland, Maaninka, Halolantie 31, 71750 Maaninka, Finland b Agrifood Research Finland, Soil and Environment, 31600 Jokioinen, Finland
Received 18 November 2005; received in revised form 16 March 2006; accepted 25 March 2006
Abstract The aim of this study was to investigate the dynamics of ammonia (NH3) volatilization from intensively managed pastures on a soil type typical of the dairy production area in Finland and to clarify the effect of rainfall on NH3 volatilization. The study included two experiments. In Experiment 1 the total amount of NH3–N emitted was calculated based on the annual surface coverage of dung (4%) and urine (17%). The application rate of total N in the simulated dung and urine patches was approximately 47 g N m2 and 113 g N m2, respectively. In Experiment 1 the general level of NH3 emissions from the urine patches was high and the peak volatilization rate was 0.54 g NH3–N m2 h1. As expected, emissions from the dung pats were clearly lower with a maximum rate of 0.10 g NH3–N m2 h1. The total emission calculated for the whole pasture area (stocking rate four cows ha1 y1, urine coverage 17% and dung coverage 4%) was 16.1 kg NH3–N ha1. Approximately 96% of the total emission originated from urine. In Experiment 2 we measured the emissions from urine only and the treatments on the urine patches were: (1) no irrigation, (2) 5+5 mm and (3) 20 mm irrigation. The peak emission rates were 0.13, 0.09 and 0.04 g NH3–N m2 h1 and the total emissions were 6.9, 3.0 and 1.7 kg NH3–N ha1, for treatments (1), (2) and (3), respectively. In both measurements over 80% of the total emission occurred during the first 48 h and there was a clear diurnal rhythm. Increasing rainfall markedly decreased NH3 emission. Volatilization was highest with dry and warm soil. The JTI method appeared to be suitable for measuring NH3 volatilization in this kind of experiment. According to our results, the importance of pastures as a source of NH3 emission in Finland is minor. r 2006 Elsevier Ltd. All rights reserved. Keywords: Ammonia; Nitrogen; Pasture; Gaseous emissions; Dairy cattle; Finland
1. Introduction Corresponding author. Tel.: +358 17 2644 821;
fax: +358 17 2644 851. E-mail addresses: kirsi.saarijarvi@mtt.fi (K. Saarija¨rvi), pasi.mattila@helsinki.fi (P.K. Mattila), perttu.virkajarvi@mtt.fi (P. Virkaja¨rvi). 1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.03.052
Ammonia (NH3) volatilization is a major pathway of nitrogen (N) emissions from agriculture. In 1995, the estimated amount of NH3 emissions in Finland was 35 000 t. Up to 90% of the total amount originates from agriculture, mainly from
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slurry and manure spreading (Gro¨nroos et al., 1998). The risk of NH3 volatilization is greatest when slurry is broadcast on the soil surface during warm and windy weather. According to previous studies, over 20% of the total N from surfacespread cattle slurry may be lost by volatilization (Mattila and Joki-Tokola, 2003). Excreta is also deposited on the soil surface in grazing. In intensive grazing, the total amount of N deposited in dung and urine may be considerable, since about 60–80% of the N ingested by the cows is returned to the pasture in dung and urine (Haynes and Williams, 1993). NH3 emission is dependent on the wind speed, air temperature and soil properties such as pH, moisture, texture, cation exchange capacity (CEC) and temperature, (Bolan et al., 2004). Because of the large variation in NH3 emission caused by climatic and soil conditions, further local research is needed in order to make accurate estimates of regional emissions (Bolan et al., 2004, Bussink, 1996). In particular, none of the previous NH3 emission studies provides valid information on pastures in northern latitudes, as the typical CEC is low (o20 cmol kg1) and the amount of rainfall is usually fairly high (4300 mm) during summers. There are several methods available for measuring NH3 emissions. The most commonly used in previous studies are the mass balance, wind tunnel and micrometeorological methods (Ross and Jarvis, 2001, Bussink, 1996). In this study we used the micrometeorological chamber technique (JTI method; Svensson, 1994). Earlier, the JTI method was used for measuring NH3 volatilization from evenly spread manure or fertilizer (Mattila and JokiTokola, 2003; Rodhe and Rammer, 2002; Misselbrook and Hansen, 2001). The results obtained from comparison of the JTI and integrated horizontal flux (IHF) methods were fairly uniform, even though it was concluded that the JTI method could overestimate emissions higher than 400 g N ha1 h1 (Misselbrook and Hansen, 2001). As the method should be suitable for measuring volatilization from small plots, we studied NH3
emissions from simulated average-sized dung and urine patches. The aim of this study was (1) to investigate the dynamics of NH3 volatilization from intensively managed pastures on a soil type typical of the dairy production area in Finland and (2) to clarify the effect of rainfall on NH3 volatilization. 2. Material and methods 2.1. Experimental site and design The study was carried out during the summers of 2002 and 2003 at Agrifood Research Finland (MTT), North Savo Research Station, Maaninka (631100 N, 271180 E). The soil texture at a depth of 0–10 cm was mainly fine sand (Table 1). The soil moisture content was measured by time domain reflectometry (TDR, Delta-T devices, Cambridge, UK). The soil and air temperatures and the air moisture content were measured by Hobo H8 (Onset Computer Corporation, Boume, MA, USA) and wind speed by a cup anemometer (Wilh. Lambrecht GmbH, Go¨ttingen, Germany) at a height of 2 m. In the experiments the total amount of NH3–N emitted was calculated based on the previously determined annual percentage surface coverage of dung and urine (4% and 17% of the pasture per year, respectively) at the average intensive grazing pressure (herbage allowance 25 kg dry matter (DM) cow1 d1, average stocking rate four cows ha1 y1). The average mass and area of urination and defecation were measured earlier (2.37 kg and 0.35 m2 for urine and 2.47 kg and 0.08 m2 for dung) and the data were used in the experiments. Total N, NH4–N, DM concentrations and pH values of the urine and dung used in Experiment 1 (Exp 1) and Experiment 2 (Exp 2) are presented in Table 2. The application rate of total N in the simulated dung and urine patches was approximately 47 g N m2 and 113 g N m2, respectively. Fresh urine and dung were collected directly from grazing dairy cows in the morning on the first day of each measurement. Samples were taken for the
Table 1 Soil properties (0–10 cm) at the experimental sites
Exp 1 Exp 2
0.002 mm (%)
0.002–0.02 mm (%)
0.02–0.2 mm (%)
0.2 mm (%)
pH
CEC (cmol kg1)
7.7 11.6
11.9 20.7
73.5 49.9
6.9 17.8
6.13 5.86
4.0 3.4
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Table 2 Total N, NH4–N, urea and DM concentrations and pH values of the urine and dung used in Experiments 1 and 2
Experiment 1 Measurement Measurement Measurement Measurement
Total N (g l1)
NH4–N (g l1) fresh urine
NH4–N (g l1) after 48 h
DM (%)
pH
1 2 1 2
Dung Dung Urine Urine
3.8 3.2 7.4 7.5
0.24 0.18 0.04 0.06
nd nd 5.8 5.9
11.9 10.0 5.4 4.8
6.6 6.8 8.5 8.3
Experiment 2 Measurement 1 Measurement 2
Urine Urine
7.5 8.3
0.05 0.06
5.8 6.5
5.1 5.4
8.3 8.4
analysis of total N (Kjeldahl N), ammoniacal N, DM content and pH by the methods used by Kemppainen (1989) (Table 2). The analysis of ammoniacal N included extraction with a solution containing HCl and CaCl2 and subsequent determination of ammonium by distillation of the extract. Before the analysis, samples were stored at 4 1C, except for one urine sample that was stored at room temperature for 48 h to allow the urea N to be converted to the NH4 form. NH3 volatilization was measured with the equilibrium concentration technique (JTI method; Svensson, 1994). The method employs passive diffusional NH3 samplers which are placed at the soil surface both in ambient air and inside chambers that have a constant ventilation rate. The method gives the amount of volatilized NH3 per area and unit of time in the weather conditions prevailing in the ambient air during the measurement. An ambient air sampler holder was placed in the middle of each artificial urine or dung patch. Urine or dung was also applied to the whole area covered by each chamber at the same rate as to the artificial patch. Each replicate consisted of one patch for ambient air measurement and one chamber. The thickness of the laminar boundary layer under the chambers (Llbl,ch) was measured by exposing L-type samplers (Svensson, 1994) in one chamber of each treatment. To estimate the total amount of volatilized N, NH3, the emission between measurement periods was interpolated taking into account the temperature and wind speed during the intervals (Malgeryd, 1996). In Exp 1, measurements were made also at night, but these results may be affected by the condensation of water inside the chambers. Therefore, the results from night measurements were not used when calculating the total NH3–N emission.
Exp 1 comprised two measurements in 2002 (Table 3). The first one lasted for 5 days (June 17–21) and the second was prolonged to 8 days (August 26–September 2) based on the results from the first measurement (Table 4). The experimental field was a second-year timothy-meadow fescue sward. Two hours before the experiment started the grass was cut to 10 cm which is the recommended post-grazing sward height in Finland (Virkaja¨rvi et al., 2002). The whole experimental area was fertilized on May 14 with 100 kg ha1 N, 48% of which was in the form of NO3–N and the rest in the form of NH4–N. The area for the second measurement was also cut and fertilized on June 18 with 100 kg N ha1 and then cut again on August 26. There were four replicates for both urine and dung and one background patch. Each measurement period lasted for 90 min, except when the temperature was below 16 1C when the duration was extended to 120 min. Exp 2 comprised two measurements in 2003, the first on June 24–July 2 and the second on August 18–26. Both measurements lasted for 8 days (Table 3). Exp 2 was performed on a first-year timothymeadow fescue sward cut to 10 cm 2 h before the experiment started. The whole area was fertilized on May 20 with 88 kg ha1 N. The area for the second measurement was also cut and fertilized on June 18 with 80 kg ha1 N and on July 31 with 52 kg N and cut again on August 18. In all fertilization applications, 48% of the N was in the form of NO3–N and the rest in the form of NH4–N. The treatments in Exp 2 were: (1) no irrigation, (2) 5+5 mm irrigation and (3) 20 mm irrigation. The first irrigation in treatments 2 (5 mm) and 3 (20 mm) was applied between periods 1 and 2 and the second irrigation for treatment 2 was applied
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Table 3 Measured treatments and timing of measurement periods in Experiment 1 (U ¼ urine, D ¼ dung) and in Experiment 2 Period
N
Experiment 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 4 4 4 4 4 4 4 4 4 4 4 4 4 4
Experiment 1 2 3 4 5 6 7 8
2 3 3 3 3 3 3 3 3
Date
Time
Hour
17.6.
14:00 16:00 20:00 2:00 9:30 15:00 20:00 2:00 9:30 15:00 20:00 9:30 15:00 15:00
1 3 7 13 21 26 31 37 45 50 55 69 74 98
12:00 17:00 10:30 15:30 15:00 15:00 12:00 18:00
1 6 24 29 52 76 121 199
18.6.
19.6.
20.6. 21.6. 24.6. 25.6. 26.6. 27.6. 29.6. 2.7.
Measured treatment
Date
Time
Hour
Measured treatment
U U U U U U U U U U U U U U
26.8.
14:00 17:00 20:00 2:00 9:30 15:00 20:00 2:00 9:30 15:00 20:00 15:00 14:00 15:00
1 4 7 13 21 26 31 37 45 50 55 74 97 122
U U U U U U U U U U U U U U
13:00 17:00 10:00 14:00 13:00 13:00 13:30 11:30
1 5 23 27 50 74 122 192
20 and 5 mma
D
27.8. D 28.8. D 29.8. 31.8. 2.9.
D
20 and 5 mma
18.8.
5 mmb
19.8. 20.8. 21.8. 23.8. 26.8.
D
D
D
D
5 mmb
Timing of the irrigation treatments and measurement periods in Experiment 2. Only urine was applied in Exp 2. a 20 mm and first part of the 5+5 mm irrigation was given between measurements 1 and 2. b Second part of the 5+5 mm irrigation was given between measurements 3 and 4.
Table 4 Average values of applied N and NH3 emissions from the dung pats and the urine patches in Experiment 1 and from the 0, 5+5 and 20 mm irrigated urine patches in Experiment 2 Experiment 1
Experiment 2
Urine
SE
Dung
SE
0 mm
SE
5+5 mm
SE
20 mm
SE
Measurement 1 Applied total N g Applied as urea and NH4–N g Lost as NH3–N g NH3–N volatilization % of total N
17.5 13.7 3.2 18.4
– – 0.48 2.76
9.3 0.6 0.1 1.2
– – 0.01 0.09
16.2 12.9 1.3 8.0
– – 0.34 2.09
16.2 12.9 0.6 3.7
– – 0.1 0.62
16.2 12.9 0.4 2.2
– – 0.06 0.37
Measurement 2 Applied total N g Applied as urea and NH4–N g Lost as NH3–N g NH3–N volatilization % of total N
17.8 13.9 3.2 17.8
0.73 4.09
7.8 0.4 0.1 1.4
– – 0.01 0.18
19.6 15.7 1.5 9.5
– – 0.37 2.29
19.6 15.7 1 6
– – 0.16 0.97
19.6 15.7 0.4 2.5
– – 0.07 0.44
SE ¼ standard error of mean.
(5 mm) between periods 3 and 4. The duration of each measurement period was 90 min. There were three replicates of the irrigation treatments and a background patch.
3. Results The samplers exposed in ambient air and the Ctype samplers of the chambers were not over-
ARTICLE IN PRESS exposed and, therefore, no results were lost due to overexposure. The L-samplers exposed under the chambers were supersaturated during periods with high NH3 volatilization, but useful results were obtained for the calculation of Llbl,ch from about half of the periods (data not shown).
NH3-N g m-2 h-1
K. Saarija¨rvi et al. / Atmospheric Environment 40 (2006) 5137–5145
3.1. Experiment 1
Urine Dung
Air temp C
Ground temp C
Wind speed m/s
25 C/m/s
The general level of NH3 emissions from the urine patches was high. The highest volatilization rates were 0.34 and 0.54 g NH3–N m2 h1 in June and August, respectively. As expected, emissions from the dung pats were clearly lower with a maximum rate of 0.10 g NH3–N m2 h1. The volatilization followed the typical pattern, being high in the afternoon and low at night. The total amount of volatilized NH3–N from the urine patches was over five times greater than from the dung pats. In June, the NH3 volatilization especially from the dung pats remained appreciable between 48 and 96 h after application. Therefore, measurement in August was prolonged to 168 h. However, the volatilization rate remained low (o0.7 g NH3–N m2 h1) between 31 and 168 h after the application. The daytime temperatures were fairly similar in June and August (means 19.9 and 18.2 1C, respectively, Fig. 1). At night the temperature was slightly higher in June than in August (means 13.6 and 11.7 1C, respectively). The relative humidity followed a diurnal pattern with a typical daytime minimum of 32–50% and a night-time maximum near 100%. In June the wind speed was typically between 0 and 2 m s1 but increased between 48 and 80 h to a maximum of 8.3 m s1. In August the wind speed was between 0 and 4.9 m s1. The soil was extremely dry in the beginning of both measurements. The TDR probe showed soil moistures of 0.104 m3 m3 and 0.090 m3 m3 for June and August, respectively. The precipitation during measurement 1 was 4.5 mm, of which 4.1 mm was on day 1 between 3 and 7 h after application. During measurement 2 the total precipitation was 22.9 mm, of which 1.8 mm occurred 50 h after application 6.3 mm between 74 and 97 h after application 13.2 mm between 97 and 122 h after application. The soil temperature range in depth of 10 cm in June was 21.0–14.1 1C (mean 17.5 1C). Data from August are not available because of equipment failure.
0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 30
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20 15 10 5 0 0
24
48 72 Hours after application
96
Fig. 1. NH3 volatilization from artificial dung and urine patches, air temperature and wind speed during measurement 1 in Experiment 1 in June 2002. Vertical bars represent SE.
3.2. Experiment 2 The NH3 volatilization from the 0 mm irrigation urine patches was lower than in Exp 1. The emission peaks were 0.09 and 0.13 g NH3–N m2 h1 in June and August, respectively (June; Fig. 2). The peak emission from the 5+5 mm treatment in June was 0.071 g NH3–N m2 h1 but, in August the peak value was the same as from the 0 mm treatment. The peak values from the 20 mm treatment were 0.04 and 0.03 g NH3–N m2 h1 in June and August, respectively. The total NH3–N emission from the 0 mm treatment was less than half that of the previous year (Table 4). However, without precipitation the proportion of volatilized NH3–N of the total N applied was almost twice that from the 5+5 mm treatment and four times greater than from the 20 mm treatment. Daytime temperatures in June were a little higher than in August (means 18.1 and 16.6 1C, respectively). The night-time temperatures were similar (means 12.1 and 12.6 1C, respectively). The relative humidity followed a diurnal pattern with a typical daytime minimum of 36–60% and night-time maximum near 100%. In June the wind speed exceeded 3 m s1 (peak 3.7 m s1) only twice briefly during the first period. The rest of the measurement
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20 mm irrigation and first part of the 5 + 5 mm irrigation
0.18
0 mm
NH3-N g m-2h-1
0.16
5 + 5 mm
0.14
Second part of the 5 + 5 mm irrigation
0.12
20 mm
0.10 0.08 0.06 0.04 0.02 0.00 30 Air temp C
Ground temp C
Wind speed m/s
25
C/m/s
20 15 10 5 0 0
24
48 72 Hours after application
96
120
Fig. 2. NH3 volatilization from artificial urine patches, air and ground temperature and wind speed during measurement 1 in Experiment 2 in June 2003. Vertical bars represent SE.
periods in June and throughout measurement periods in August the wind speed remained below 3 m s1. The soil moisture was high at the beginning of both measurements with TDR showing soil moistures of 0.345 m3 m3 and 0.347 m3 m3 for June and August, respectively. The precipitation in June was 1.4 mm and in August 8.6 mm. The soil remained moist throughout the measurements. The soil temperature range at a depth of 10 cm was 17.3–11.5 1C (mean 14.4 1C) and 16.9–12.2 1C (mean 14.9 1C) in June and August, respectively. 4. Discussion The JTI method appeared to be applicable to the kind of measurement carried out here. The edge effect certainly lowers the NH3 concentration in the ambient air above a urine or dung patch, but this corresponds to the actual situation with genuine patches and should not bias the results. However, the NH3 concentration in the ambient air over a pasture with many urine and dung patches may be somewhat higher than in an experiment with only a few patches.
4.1. Effect of treatments Even though the peak emission rates found during the first day of the measurements were high, the proportional emissions over the entire measurements were on a moderate level (1–17% of applied N) compared with the large variation in the literature (3–52%) (Sherlock and Goh, 1984; Ryden et al., 1987; Petersen et al., 1998; Whitehead and Raistrick, 1993). The NH3 emission from dung was less than 5% of the total N applied. This result is in line with other studies (Petersen et al., 1998). The slight increase 74 h after application in June in Exp 1 was probably caused by high wind speed and a large number of insect holes on the surface crust of the dung pats. The peak NH3 emission rates from urine in Exp 1 were high (Figs. 1 and 2) compared with the results of Misselbrook and Hansen (2001) who measured 898 and 905 g NH3–N ha1 h1 by the JTI method from granulated urea and band-spread cattle slurry, respectively, applied to grassland. However, since they used low N application rates (138 kg N ha1 urea, 50 kg NH4–N ha1 slurry), the
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NH3 volatilization is in fairly good agreement with our experiment. Mattila and Joki-Tokola (2003) measured, on average, 3700 and 2000 g NH3–N ha1 h1 by the JTI method from broadcast and band-spread cattle slurry, respectively, during the day of application to ley. These figures are well in line with ours. The relative N loss from urine is lower than that from slurry obviously because of the greater infiltration of urine into the soil. Irrigation of 5+5 mm reduced the NH3 volatilization by 46% and 20 mm by 75% (Fig. 2). Heavy rainfall is known to diminish NH3 volatilization (Bussink, 1996; Whitehead and Raistrick, 1991). However, light rainfall (o5 mm) has increased NH3 volatilization (Bussink, 1996). In our case, the first irrigation of 5 mm given immediately after the first measuring period (1.5 h after application) diminished the NH3 volatilization by ca. 20% compared to the no irrigation treatment. The major part of the decrease occurred after the second 5 mm irrigation applied 25.5 h after application (between periods 3 and 4). In Exp 1, the total emission from the pasture was 16.1 kg NH3–N ha1 when the relative coverage percentages of dung and urine were taken into account. Approximately 96% of the total emission originated from urine. In Exp 2, multiplying the amount of NH3–N volatilized from the urine patches (mean of measurements 1 and 2) by the coverage percentage of urine on pasture gave emissions of 6.9, 3.0 and 1.7 kg NH3–N ha1 for the irrigation treatments of 0, 5+5 and 20 mm, respectively. In both experiments, the calculated total emission was comparable with Bussink (1996) who measured 9.1 kg total NH3–N emission from pasture fertilized with 250 kg N ha1. In our study we did not measure the NH3–N volatilization from fertilizers, and this probably lowers the total emission from the pasture. However, according to the literature, the amount volatilized from granulated fertilizers is small (Sommer et al., 2004), and thus our results should give a relatively accurate estimate of the total NH3–N emission. 4.2. Factors affecting NH3 emission NH3 emission is dependent on the soil pH, moisture, texture, (CEC) and temperature, as well as on the wind speed and air temperature (Bolan et al., 2004). The N concentration and hippuric acid content of urine are also important factors (Petersen et al., 1998).
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In both our experiments, measurements from June and August were very similar, but there was a large difference between the experiments in respect of peak concentrations and the total amount of NH3 volatilized. Overall, the level of volatilization in Exp 2 was only half that of Exp 1. The pH value of the soil in Exp 1 was slightly higher than in Exp 2, which could partly explain the higher emission rate (Table 1). The measured CEC value of the soil was so low in both experimental areas (o10 cmol kg1) that, according to Whitehead and Raistrick (1993), it could not have affected the emission rates. As the weather conditions (air temperature and rainfall) were also comparable during the experimental years, the reason for the difference in the amount of volatilization could be in the soil parameters. This is also supported by the fact that the NH3 concentration inside the chamber, where the influence of the varying wind conditions on the ambient air is minimal, was over three times higher during day 1 in Exp 1 than in Exp 2 (data not presented). Soil moisture and temperature are known to influence the NH3 emission from urine (e.g. Whitehead and Raistrick, 1991; Haynes and Williams, 1993). The greatest difference between Exp 1 and 2 occurred in the soil moisture content at the beginning of the experiments. In Exp 1 the soil was dry, even hydrophobic (soil volumetric water content ca. 10%) when applying the treatments. In Exp 2, on the contrary, the soil volumetric water content at the beginning of the measurements (ca. 35%) exceeded the water holding capacity ca. y 30% at 0.1 MPa measured from the same area by Pietola et al. (2004). Previously wet soil has increased volatilization compared to dry soil (Whitehead and Raistrick, 1991), but in our case the outcome was the opposite. We suggest that this was partly caused by hydrophobic soil conditions, which could have caused the urine to spread on larger surface area in Exp 1 than in Exp 2 and partly by soil temperature which was on average over 3 1C and occasionally over 5 1C higher in Exp 1 than in Exp 2 (Figs. 1 and 2). The importance of soil temperature for NH3 volatilization is supported by van der Putten and Ketelaars (1997). According to Rachhpal-Singh and Nye (1986a,b), the increase in volatilization with increasing temperatures is partly caused by increased urease activity, partly by a greater proportion of the ammoniacal N being present as NH3 gas and partly by faster
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diffusion. For example, urea hydrolysis in soil increased with increasing temperatures from 10 to 40 1C (Vlek and Carter, 1983) while the volatilization increased with increasing temperature up to 20 1C (Whitehead and Raistrick, 1991). Studies made in stable laboratory conditions do not take into account the diurnal temperature rhythm that markedly lowers the temperature of wet soil during the nights and also slows down the warming of the soil during the days. Consequently, a high daytime air temperature is an inadequate descriptor of the soil temperature when the soil volumetric water content is high, as it was in our case. In conclusion, the most important reason for the higher NH3 volatilization in Exp 1 was the combination of dry soil and, consequently, high soil temperatures during the afternoons. The N concentration of the urine was a little higher than average level based on the literature (Bussink, 1996; Petersen et al., 1998) and N concentration of total diurnal urine (6.96 g l1) collected from six cows fed pasture grass indoors on three separate occasions (Sairanen, unpublished). As the difference in N concentration between the years was small, the urine N concentration probably had a minor effect on NH3 volatilization. The hippuric acid concentration of the urine was not measured.
between 20% and 60% of the emitted NH3 is deposited within 2 m. Based on these results, the volatilization of NH3 from pasture is of minor importance and grazing needs little attention as a source of NH3 emissions in Finland.
4.3. The importance of the results
We wish to thank Heikki Riisio¨, M.Sc., for his excellent assistance in the field work and Dr. Helvi Heinonen-Tanski for her valuable comments on the manuscript. This work was financially supported by the Finnish Cultural Foundation and the Finnish Ministry of Agriculture and Forestry.
Compared with our results, some of the previous national NH3 emission estimates of Finnish pastures are overestimates. Kera¨nen and Niskanen (1987) use the results of Buijsman et al. (1987) and estimate that 5% of the dung N and 40% of the urine N are volatilized during grazing. Pipatti (1990) gives a figure of 6.5 kg NH3–N y1 cow1 during the grazing season, while our result 16.1 kg NH3–N ha1 transforms to 4.0 kg NH3–N y1 cow1 when divided by average stocking rate of four cows ha1 y1. As the weather conditions during the Exp 2 were more comparable to the average Finnish summer than in the Exp 1, the actual total volatilization is probably even lower than that. The pasture area in Finland is approximately 110 000 ha. The annual NH3 emission from pastures calculated from our results is 710–1570 t. This is only 2.3–5% of the total NH3 emission caused by agricultural activities (Gro¨nroos et al., 1998). Furthermore, according to Ross and Jarvis (2001),
5. Conclusions 1. The dynamics of NH3 volatilization were well in line with previous research. Over 80% of the total emission occurred during the first 48 h and a clear diurnal rhythm of volatilization was observed. 2. Increasing rainfall markedly decreased NH3 emission. 3. The most important factor explaining the differences in volatilization in this experiment was the combination of soil moisture content and soil temperature. Volatilization was highest with dry and warm soil. 4. The JTI method appeared to be applicable for measuring NH3 volatilization from simulated urine and dung patches. 5. According to our results, the importance of pastures as a source of NH3 emission in Finland is minor and has been overestimated previously. Acknowledgments
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