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Keywords:

  • ammonia volatilization;
  • ammonium nitrogen;
  • grassland;
  • slurry;
  • surface application

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

The objective of this paper is to determine ammonia (NH3) volatilization factors (as a ratio of volatilized NH3-N to applied ammonium nitrogen [NH4-N]) following the application of dairy cattle slurry to grassland surface based on the results of a number of pot and field experiments. Pot experiments examined the effects of both environmental factors (soil water condition and air temperature) and properties of the slurry (dry-matter content, NH4-N content and pH) on NH3 volatilization loss from slurry applied to the soil surface in a pot where grass was grown. A grassland field trial was also carried out to confirm the results from the pot experiments. Our results demonstrated that a slight application rate (<60 Mg ha−1), dry soil water conditions, low air temperature, low NH4-N content in the slurry, low dry-matter content and low pH of the slurry, and acidification by adding superphosphate to the slurry, could abate volatilization. Our experiments also showed that the volatilized NH3-N was basically determined by the application rate of NH4-N from the slurry, even though the slurry was applied at different rates and under conditions that affect NH3 volatilization. From these results we estimated the cumulative volatilization loss of NH3 from the surface-applied slurry from the time the slurry was applied until volatilization was complete and then calculated the volatilization factor. It could be deduced from this calculation that the recommended values of the volatilization factor (g NH3-N [g NH4-N]−1) from the surface-applied slurry were as follows: 0.32 when the application rate of the slurry was less than 6 kg m−2 (60 Mg ha−1); 0.42 when the rate was more than 6 kg m−2; 0.37 when the rate was unknown.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

Cattle manure, such as barnyard manure, slurry and liquid manure, is usually applied to the surface of grasslands in grassland dairy farming. The surface application of manure, however, is a major source of complaints from the public because of the offensive odor and the volatilization of ammonia (NH3) to the atmosphere. Volatilized NH3 is a potent atmospheric pollutant with a wide variety of environmental impacts. Ammonia is a chemically active gas and readily combines with nitrate and sulfate in acid cloud droplets to form particulates (Asman et al. 1998). The formation of particulates prolongs their existence in the atmosphere and, therefore, influences the geographic distribution of acidic depositions (Sommer and Hutchings 2001). In addition, NH3 volatilization not only results in a significant reduction in the nitrogen (N) fertilizer value of the manure (Matsunaka et al. 2003), but is also, following transport and deposition, associated with eutrophication of aquatic systems, soil acidification and disturbance of the nutrient balance in trees and soil because it can raise N fertility levels in nutrient-poor soil, such as forest soil (Roelofs and Houdijk 1991; Sommer and Hutchings 2001). Furthermore, a major source of atmospheric NH3 is agricultural farming, which contributes to more than 50% of global NH3 volatilizations (Food and Agriculture Organization and International Fertilizer Industry Association 2001) and contributes over 70% in intensive livestock farming areas in Europe (Buijsman et al. 1987) and Japan (Hojito et al. 2006).

In Japan the control of NH3 volatilization during and following the application of manure to minimize both the risk of environmental pollution and the reduction in the N fertilizer value of the manure is a serious problem. Nevertheless, there is little information on NH3 volatilization from animal manure applied to grassland surfaces in Japan (Matsumura 1988; Saito et al. 1989) and we have very little information about the volatilization factor, which is defined as the ratio of volatilized NH3 to applied ammonium N (NH4-N) in this paper.

We have been carrying out several experiments to examine the effects of both environmental factors (soil water condition and air temperature) and properties of dairy cattle slurry (dry-matter content, NH4-N content and pH) on NH3 volatilization from the applied slurry. The objective of this paper is to determine NH3 volatilization factors following the application of dairy cattle slurry to grassland surfaces based on the results of a number of pot and field experiments.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

Pot experiments

Pot experiments were conducted from 1999 to 2000. In all our experiments we used plastic pots with a surface area of 0.02 m2 and a depth of 18 cm. The pots were filled with surface layer Gray Upland soil (Aeric, Typic Epiaquults) from our experimental farm. To keep the bulk density of the soil at field conditions, we filled the pot with 2.7 kg of soil on a dry soil basis, with a depth of up to 13 cm of soil in the pot, because the bulk density of the soil was 1.02 g cm−3. This careful soil filling avoided any effect of differences in bulk density of the soil in the pots on NH3 volatilization as differences in the bulk density of the soil may affect infiltration of NH4-N in the applied slurry. Before filling the pots with soil, P2O5 as superphosphate and K2O as potassium sulfate were applied to the soil at a rate of 1.0 and 0.5 g pot−1, respectively, and mixed well with the soil. As the pH of the soil used in our experiments was less than 5.5, we applied commercial calcium carbonate based on the result of a buffer curve of the soil to improve soil acidity. The target soil pH was 6.5. No chemical fertilizer N was applied to the pots in our experiments. We maintained a soil matric water potential in the pots of –31 kPa by irrigation of deionized water twice or three times per day until just before the application of the slurry. No irrigation was conducted in the 120 h following the application of the slurry, which is the time for measurement of NH3 volatilization. The chemical properties of the original soil used in the experiment were as follows; pH(H2O), 5.1; total N and C, 2.5 and 36.3 g kg−1, respectively; available P measured using the Bray No. 2 method, 0.18 g kg−1; cation exchange capacity, 26.8 cmol(+) kg−1; exchangeable K, Ca and Mg, 0.36, 1.65 and 0.19 g kg−1, respectively.

Orchardgrass (Dactylis glomerata, L., var. Okamidori) was sown in late April and cut after growing for approximately 50 days. We applied the slurry to the soil surface of the pots 4 or 5 days after cutting the grass. The slurries used in the experiments were derived from excreta from dairy cattle. Some chemical properties of the slurries in each experiment are shown in Table 1. The application rate of the slurry usually followed three levels, except for some experiments described later; no slurry was used as a control, 6 kg m−2 (60 Mg ha−1) is the recommended rate in Hokkaido, Japan, to avoid environmental pollution (Matsunaka et al. 1988) and 12 kg m−2 (120 Mg ha−1) is considered to be a heavy application.

Table 1.  Some chemical properties of the cattle slurries used in the experiments
ExperimentpHEC (S m−1)DMC (g kg−1)Total C (g kg−1)N (g kg−1)P (g kg−1)K (g kg−1)
NumberFactorRemarksNH4-NOrg. NTotal N
  • Org. N, Organic N = Total N – NH4-N, because NO3-N was not detected in all cases. EC, electric conductivity; DMC, dry matter content of the slurry.

1Soil cover 6.91.95 7327.32.01.93.91.33.0
2Soil water condition 7.11.7912946.51.83.14.91.94.1
3-1Temperature5 and 10°C7.82.2413145.62.33.35.61.56.3
15°C7.71.81 8841.42.33.76.01.55.4
3-2Temperature10°C7.41.9411640.52.03.15.11.35.3
15°C7.22.1212241.91.83.35.11.35.5
20°C7.22.1111740.51.93.15.01.35.5
4NH4-N contentAeration8.92.02 5516.40.92.73.61.02.4
No aeration7.61.36 5719.71.92.74.60.92.0
5DMC (dilution)Raw slurry7.32.4312437.62.02.54.51.24.9
Twofold dilution7.51.43 6218.41.01.22.20.62.5
Threefold dilution7.51.04 4110.90.70.81.50.41.8
6pHLow6.61.85 8935.31.72.44.10.64.0
Middle6.92.22 8331.12.02.94.91.04.5
High7.11.89 8130.61.92.74.61.23.7
7AcidifyingRaw slurry7.52.3312236.72.13.75.81.55.8
Field Experiment Autumn7.71.97 7024.42.02.64.61.44.3
Spring7.41.9310335.72.12.95.01.35.2
Summer7.02.12 8327.22.12.34.41.14.9

We carried out the pot experiments in a glasshouse at Rakuno Gakuen University, except for experiments involving air temperature. To prevent increasing the air temperature in the glasshouse, all windows remained opened all day. The mean air temperature in the glasshouse, however, ranged from 15 to 25°C because the experiments were generally conducted over the summer season. All experiments were conducted with three replicates.

Measurement of NH3 volatilization

We covered the pot with a hood as illustrated in Fig. 1 and trapped the volatilized NH3 following the application of slurry into 40 g L−1 boric acid using a vacuum pump with a suction power of 0.3 m3 h−1. The boric acid solution received indicator reagents of both methyl red and bromocresol green. The solution was titrated by 0.01 mol L−1 sulfuric acid to determine the volatilized NH3-N. Measurements were continued for 120 h following the application of the slurry. The volatilized NH3 was calculated by subtracting the amount of volatilized NH3 in the control pots from the amount in each treatment receiving the slurry.

image

Figure 1. Outline of the trapping equipment used to determine volatilized NH3-N from surface-applied cattle slurry.

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Details of the pot experiments

Experiment 1

Only this experiment was conducted using no grass growing pots to confirm NH3 volatilization from the surface-applied slurry and to determine the effect of soil cover following the application of slurry on volatilization. The slurry and chemical fertilizers (urea and ammonium sulfate) were applied to the soil surface. The application rate of the slurry was 10 kg m−2 and NH4-N as the chemical fertilizer was applied at a rate of 25 g m−2. We covered the applied slurry with soil to a depth of 2 cm just after the application of the slurry.

Experiment 2

The effect of soil water condition on NH3 volatilization was examined at three levels, wet, medium and dry. The soil water matric potential in each level was −3, −31 and −310 kPa, respectively. The method of maintaining the water conditions is the same as that described above.

Experiment 3

The effect of air temperature during the experiment on the volatilization was examined. This experiment was conducted twice as follows; the first experiment (Experiment 3-1) was done under relatively low temperature levels (5, 10 and 15°C) and the second experiment (Experiment 3-2) was done at high temperature levels (10, 15 and 20°C). We used a growth chamber to control temperatures over 10°C. A large refrigerator room with enough light for plant growth was used for the 5°C treatment. As we had only one growth chamber suitable for the experiment, these experiments were conducted on different dates, although treatments of 5 and 10°C in Experiment 3-1 could be done at the same time using both the refrigerator room and the growth chamber. The temperature was kept stable at each treatment level during the experimental period.

Experiment 4

The effect of the NH4-N content in the slurry on volatilization was examined. We treated the slurry with aeration to change the NH4-N content in the slurry. The NH4-N content decreased with aeration, but the pH of the slurry increased and the other properties of the slurry changed slightly (Table 1). In this experiment we only used the recommended application rate and the measurement period of NH3 volatilization was 96 h.

Experiment 5

Three levels of dry-matter content (DMC) of the slurry were examined in this experiment. We prepared the slurries by diluting them twofold or threefold with deionized water prior to application. To avoid the effect of differences in the application rate of NH4-N derived from the slurry on volatilization, we applied 20 g m−2 as NH4-N from the slurries. As the original DMC in the raw slurry was 124 g kg−1, DMC in the twofold and threefold diluted slurries were 62 and 41 g kg−1, respectively (Table 1).

Experiment 6

We collected three types of slurries with pH values of 6.6, 6.9 and 7.1 and used them for this experiment to clarify the effect of pH of the slurry itself on NH3 volatilization.

Experiment 7

To examine the effect of lowering pH of the slurry on NH3 volatilization, we used slurry to which superphosphate was applied to decrease the pH of the slurry. The application rate of the superphosphate was the amount required to obtain a pH value of 6.5. The slurry used as a control received no superphosphate.

Field experiment

We carried out a field experiment from September 1999 to July 2000 to compare the NH3 volatilization factors found in the pot experiments with those recorded in the field. The grassland used in the experiment was timothy (Phleum pretense L., var. Nosappu) sward, which was established in 1997. In general, the grassland was cut twice per year to produce hay or silage. Some chemical properties of soil in this experimental field were as follows; pH(H2O), 6.4; total N and C, 3.0 and 40.3 g kg−1, respectively; available P measured using Bray No. 2 method, 0.25 g kg−1; cation exchange capacity, 24.9 cmol(+) kg−1; exchangeable K, Ca and Mg, 0.28, 1.71 and 0.26 g kg−1, respectively.

Vinyl chloride pipes with a cross-section area of 0.023 m2 were set into the grassland soil. The slurry was applied within the pipes at three different times: late autumn after the second cut (30 October 1999), the following spring (5 May 2000) and summer after the first cut (30 June 2000). The application rate treatments at each time were: 0, the recommended rate (6 kg m−2) and the heavy rate (12 kg m−2). We used the same equipment as illustrated in Fig. 1 to measure volatilized NH3 from the slurry applied to the grassland surfaces in the pipe. The experiment was conducted with three replicates.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

NH3 volatilization from the slurry applied to the soil surface

We clearly observed NH3 volatilization from surface-applied slurry and there was no volatilization from slurry covered with 2-cm deep soil (Fig. 2). These results confirmed that NH3 volatilization only occurs when slurry is applied to the soil surface. Among the treatments of topdressing of chemical fertilizers, only urea showed continuous NH3 volatilization and its volatilization factor, which is the ratio of volatilized NH3-N to N applied as urea, was 0.06 over a 96-h period (Fig. 2).

image

Figure 2. Change in the cumulative amount of volatilized NH3-N from surface-applied cattle slurry (SA-Slurry), chemical fertilizers (urea and ammonium sulfate [AS]) and surface-applied slurry with soil cover (Soil cover) following application over a 96-h period. Error bars indicate standard deviation (n = 3).

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Change in NH3 volatilization rate with time

The NH3 volatilization rate with time in Experiment 2 is illustrated in Fig. 3, which shows a typical pattern. In all our experiments, as shown in Fig. 3, NH3 volatilization rate increased to maximum level within 2 h following the application of the slurry in every treatment and then decreased rapidly. As the peak rate in each experiment was basically dependent on the NH4-N applied in the slurry, the volatilization rate shown in the heavy application was usually higher than that recorded with the recommended application. Each treatment with the same application rate affected volatilization, but the level of the effect was relatively small compared with the application rate of the slurry. In every experiment, there was no significant difference in the volatilization rate among treatments with the same application rate after 24 h or more after application.

image

Figure 3. Profile of the NH3 volatilization rate over 48 h of the 120-h measurement period for different soil water conditions and application rates of cattle slurry. WR, wet soil water condition (−3 kPa) and recommended application rate (6 kg m−2); WH, wet soil water condition and heavy application rate (12 kg m−2); MR, medium soil water condition (−31 kPa) and recommended application rate; MH, medium soil water condition and heavy application rate; DR, dry soil water condition (−310 kPa) and recommended application rate; DH, dry soil water condition and heavy application rate. Error bars indicate the standard deviation (n = 3).

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Cumulative amount of volatilized NH3 and its estimation

In every experiment, it was very clear that the cumulative amount of the volatilized NH3 in the heavy application rate was higher than the amount with the recommended application rate (Fig. 4). Figure 4 also clearly showed that the following conditions reduced NH3 volatilization; dry soil water conditions, low temperatures and low NH4-N content in the slurry, low DMC of the slurry, low pH of the slurry, and the addition of superphosphate to the slurry. Consequently, the cumulative amount of volatilized NH3 decreased under these conditions.

image

Figure 4. Change in the cumulative amount of volatilized NH3-N with time following the application of cattle slurry. Open and solid symbols in Experiments 2, 3, 4, 6 and 7 indicate the recommended application rate (6 kg m−2) and the heavy application rate (12 kg m−2), respectively, and the different symbols show the different treatment levels. The application rate of the slurry in Experiment 5 is referred to in Table 2. Each treatment level is shown in each figure. Error bars indicate standard deviation (n = 3). SP, superphosphate.

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To estimate the amount of volatilized NH3 from the surface-applied slurry we tried to analyze all our data by fitting a model to the measured NH3 volatilization loss. At first we used a model based on the Michaelis–Menten-type equation presented by Sommer and Ersbøll (1994), who fitted this type of model directly to cumulative NH3 loss data. This equation, however, did not fit well to our data (data not shown), possibly because NH3 volatilization in many of our experiments did not completely reach a steady state during the 120-h measurement period, as illustrated in Fig. 4.

We then attempted to use another type of model as illustrated in Fig. 5 and Eq. 1:

image

Figure 5. Model of the cumulative amount of volatilized NH3-N expressed using the equation: N(t) = Nmax(1 − exp( − s·t)). Nmax, total loss of NH3-N as time approached infinity; parameter s, positive constant derived from the fitting to the curve using the least square method.

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  • N(t) = Nmax(1 – exp(–s t)) (1)

This model describes the cumulative NH3 volatilization, N(t), over time, t, since the application. The model parameter Nmax is the total loss of NH3-N as time approached infinity, and the parameter s is the positive constant derived from fitting the observation using the least square method and is involved in the slope of the curve illustrated in Fig. 5. The curve fitting based on Eq. 1 was significant in each experiment (Table 2) and the observed cumulative amount of volatilized NH3-N (Vn) showed an approximate 1:1 relationship with Nmax (Fig. 6). In addition, Nmax could only be significantly estimated from NH4-N applied in the slurry (Fig. 7), even though the data in Fig. 7 included the results of all our experiments in which treatments were widely different from each other. From the results, volatilized NH3-N from the surface-applied slurry could be more precisely estimated using the following equation (Eq. 2) than that estimated using a linear regression in which R2 = 0.834.

Table 2.  NH4-N applied in the slurry (Ns), cumulative amount of volatilized NH3-N for the measurement period (Vn), estimation of cumulative volatilized NH3-N using the equation N(t) = Nmax(1 − exp( − s·t)), volatilization ratio (VR) and the volatilization factor (Vf) calculated from the estimated total volatilized NH3-N (Nmax) and Ns in each experiment
ExperimentNs (g m−2)Vn (g m−2)N(t) = Nmax (1 − exp( − s t))VR = Vn/Ns (g NH3-N (g NH4-N)−1)Vf = Nmax/Ns (g NH3-N (g NH4-N)−1)
NumberFactorApplication rate of the slurry (kg m−2)Level of the factorNmax (g m−2)sCurve fittingR2Application rate of the slurryApplication rate of the slurry
< 6 kg m−2> 6 kg m−2< 6 kg m−2> 6 kg m−2
  • N(t) is the estimated cumulative volatilized NH3-N over time; Nmax, total loss of NH3-N as time approached infinity; parameter s, positive constant derived from the fitting to the curve using the least square method.

  • *

    P < 0.05;

  • **

    P < 0.01; n.s., not significantly different.

2Soil water condition 6−3 kPa10.8 3.0 2.80.0630.9880.27 0.26 
 6−31 kPa10.8 3.1  2.90.0700.9920.28 0.27 
 6−310 kPa10.8 2.5 3.00.0680.9900.23 0.28 
12−3 kPa21.6 9.0 9.10.0300.999 0.42 0.42
12−31 kPa21.6 8.4  7.60.0300.999 0.39 0.35
12−310 kPa21.6 7.1 7.00.0360.999 0.33 0.33
3–1Air temperature, relatively low condition 65°C13.8 5.5 5.10.0470.9590.40 0.37 
 610°C13.8  6.0 5.60.0430.9760.43 0.41 
 615°C13.8 6.9 6.70.0400.9840.50 0.48 
125°C27.610.911.10.0230.984 0.40 0.40
1210°C27.612.413.30.0190.994 0.45 0.48
1215°C27.614.515.80.0190.996 0.52 0.57
3–2Air temperature, relatively high condition 610°C12.03.73.40.0540.9440.31 0.29 
 615°C10.8 4.8 4.50.0460.9660.44 0.41 
 620°C11.4 5.1 4.90.0440.9880.45 0.43 
1210°C24.0 7.8 8.30.0220.982 0.33 0.34
1215°C21.610.711.70.0190.996 0.50 0.54
1220°C22.812.413.90.0180.999 0.55 0.61
4NH4-N content 6Aeration  5.4 1.2 1.20.0950.9750.23 0.22 
 6No aeration11.4 3.0 2.80.0930.9870.26 0.25 
5DMC10Raw slurry20.0 8.1 7.80.0790.993 0.40 0.39
20Twofold dilution20.0 7.9 8.00.0380.999 0.40 0.40
30Threefold dilution20.0  6.2 6.20.0370.998 0.31 0.31
6pH 6pH 6.610.2 2.8 2.70.0430.9990.27 0.27 
 6pH 6.912.0 3.8  3.70.0330.9940.32 0.31 
 6pH 7.111.4 3.6 3.40.0750.9860.32 0.30 
12pH 6.620.4 6.1  6.30.0260.998 0.30 0.31
12pH 6.924.0 8.4  8.60.0260.998 0.35 0.36
12pH 7.122.8 9.4 9.10.0340.985 0.41 0.40
7Acidifying 6Raw slurry12.63.94.00.0290.9990.31 0.31 
 6Superphosphate12.02.93.50.0150.9950.24 0.29 
12Raw slurry25.210.312.30.0150.999 0.41 0.49
12Superphosphate24.06.2  9.30.0090.996 0.26 0.39
Minimum        0.230.260.220.31
Maximum        0.500.550.480.61
Mean          0.33*  0.39*    0.32**    0.42**
Overall mean        0.36 n.s.0.37 n.s.
image

Figure 6. Relationship between the observed cumulative amount of volatilized NH3-N (Vn) and the predicted amount (Nmax). Line in the figure indicates the line of y = x. r, correlation coefficient.

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image

Figure 7. Relationship between the applied NH4-N from the slurry (Ns) and the predicted amount of volatilized NH3-N (Nmax).

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  • Nmax = 0.110 Ns1.43 (R2 = 0.904) (2)

where Ns is the amount of NH4-N applied in the slurry.

NH3 volatilization factor

The observed NH3 volatilization ratio (VR) was calculated using Eq. 3:

  • VR = Vn/Ns(3)

where Vn is the cumulative amount of volatilized NH3-N for the measurement period in each experiment and Ns is the amount of NH4-N applied in the slurry. The VR ranged from 0.23 to 0.50 with the recommended application and from 0.26 to 0.55 with the heavy application (Table 2). The mean VR in the recommended and heavy applications were 0.33 and 0.39, respectively, and the overall mean VR was 0.36.

As illustrated in Fig. 4, however, it appeared that NH3 volatilization did not completely finish during the measurement period in some of the experiments in which the slurry was applied at the heavy rate. This means that Vn may be underestimated compared with Nmax. The NH3 volatilization factor (Vf) should, therefore, be calculated using a revised Eq. 4:

  • Vf = Nmax/Ns(4)

because Nmax can be considered to be the total volatilization loss of NH3-N. The Vf ranged from 0.22 to 0.48 with the recommended application and from 0.31 to 0.61 with the heavy application (Table 2). The mean Vf with the recommended and heavy applications were 0.32 and 0.42, respectively. The overall mean Vf was 0.37. Consequently, the difference between Vf and VR in the heavy application rate was relatively greater than that with the recommended application rate. This confirmed the suggestion that Vn was underestimated compared with Nmax, particularly in treatments using a heavy application of slurry.

Field experiment

The Vn in each application time increased significantly with the application rate of the slurry (Table 3). Using the same application rate the effect of application time on Vn was very clear. The Vn in the autumn application was usually the lowest, followed by the spring application, and the highest was the summer application (Table 3). Therefore, the VR in the autumn application was the lowest and in the summer application it was the highest, regardless of the application rates (Table 3). The VR in the autumn application with the recommended application rate of slurry (6 kg m−2) was slightly out of range of the Vf found in the pot experiments. The VR in the spring and summer applications, however, were within the range of the Vf, regardless of the application rate of the slurry. It is, therefore, likely that the Vf found in our pot experiments can be generally adaptable to field conditions.

Table 3.  NH4-N applied from the slurry (Ns), cumulative amount of volatilized NH3-N for the measurement period (Vn) and the volatilization ratio (VR) in the field experiment
Application of the slurryNs (g m−2)Vn (g m−2)VR = Vn/Ns (g NH3-N (g NH4-N)−1)
Rate (kg m−2)Time
  1. Different letters in the same column indicate significant differences at P < 0.05 using least significant difference.

 6Autumn12.02.1 a0.18 a
 6Spring12.63.9 b0.31 b
 6Summer12.64.4 c0.35 b
12Autumn24.05.8 d0.24 c
12Spring25.27.8 e0.31 b
12Summer25.28.8 f0.35 b

Differences in VR among the application times did not correspond to differences in pH or DMC of the slurries applied at each time (Tables 1,3). With the same application rate of slurry the Ns was very similar at each application time because the NH4-N content in the applied slurries did not differ widely between application times (Tables 1,3). In addition, mean water condition in the surface layer soil (0–20 cm) during the experiment was similar among the autumn, spring and summer application times, that is, −42, −31 and −49 kPa as soil water matric potential, respectively. However, the mean air temperature during the experiment in autumn, spring and summer was 7, 11 and 20°C, respectively. This difference in mean temperature corresponded to differences in VR among application times. These results in the field also support the findings from Experiment 3.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

NH3 volatilization is controlled by two equilibriums, that is, the association–dissociation equilibrium between inline image and NH3 in the liquid phase and the partition equilibrium of NH3 between the liquid and gas phase in immediate contact with the slurry applied on the soil surface. Therefore, many factors directly or indirectly affect volatilization (Sommer and Hutchings 2001). Our experimental results were also consistent with many scientific findings, dry soil water conditions (Donovan and Logan 1983; Sommer et al. 1991), low air temperatures (Braschkat et al. 1997; Moal et al. 1995; Sommer et al. 1991, 1997), low NH4-N content in the slurry (Sommer and Hutchings 2001), low DMC of the slurry (Frost JP 1994; Sommer and Olsen 1991; Stevens et al. 1992), low pH of the slurry (Saito et al. 1989), and acidification by adding acidic substances to the slurry (Bussink et al. 1994; Frost et al. 1990; Saito et al. 1989; Stevens et al. 1989, 1992), that can reduce volatilization. NH3 volatilization from the surface-applied slurry is, therefore, affected by a multitude of factors and, hence, the proportion of NH4-N lost as NH3 is highly variable. Because of this high variation in NH3 volatilization, any model that is used to predict volatilization must include these factors to estimate the N fertilizer value of the surface-applied slurry.

A theoretical model (ALFAM model) including not only the factors discussed above but also some other factors, such as the application method, has already been used to estimate loss (Søgaard et al. 2002). We could not establish a model like ALFAM, although we found that NH3 volatilization losses under many different experimental conditions could be estimated using only the application rate of NH4-N. This might be because the applied NH4-N from the slurry was the only source of volatilization and controlled principally the amount of cumulative NH3 volatilization loss. We should remember, however, that the effect of the applied NH4-N on the cumulative amount of NH3 loss, like Nmax, was exponential rather than linear, as shown in Fig. 7. The NH3 volatilization factor is defined as the ratio of the cumulative amount of NH3 loss to the applied NH4-N in the slurry; however, this relationship is not linear but rather exponential. Thus, the cumulative amount of NH3 loss does not linearly change with the application rate of the slurry. Therefore, we have to show each NH3 volatilization factor corresponding to each application rate of the slurry when we offer the NH3 volatilization factor.

As for the NH3 volatilization factor, Stevens and Laughlin (1997) found from many experimental results that the volatilization factor ranged from 0.31 to 0.93. Our volatilization factors, which ranged from 0.22 to 0.61, using the results of Vf defined by Eq. 4, were relatively lower than the data summarized by Stevens and Laughlin (1997). A lower volatilization factor value was also found by Saito et al. (1989), who found that the factor ranged from 0.2 to 0.4.

In our experiments we examined the major factors affecting NH3 volatilization, but the factors we examined did not cover some another important factors, such as rainfall, wind speed, solar radiation, nature of the vegetative cover on the field and soil properties, such as cation exchange capacity, soil texture and hydraulic conductivity (Sommer and Hutchings 2001). In addition, we carried out only one field experiment to confirm the volatilization factors. From these conditions it is likely that our volatilization factors are not always regarded as recommended values in Japan. Even so, they are useful and valuable because there is no recommended value of NH3 volatilization factor based on the scientific results from Japan at present. Further field-scale experiments and a model describing the NH3 volatilization process from animal manure applied to grassland surface will be needed to obtain a recommendation value of the volatilization factor that can be adopted to grassland throughout Japan.

As a conclusion of this paper we suggest provisionally three NH3 volatilization factors (g NH3-N [g NH4-N]−1) because the volatilization factor should be distinguished by the application rate of the slurry. The first value is 0.32, when the application rate of the slurry is less than 6 kg m−2, the second value is 0.42, when the application rate is more than 6 kg m−2. Finally we suggest a value of 0.37 when the application rate of the slurry is unknown. These values are the mean values found in our experiments and include six factors affecting volatilization at each application rate of the slurry.

ACKNOWLEDGMENTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES

We would like to express our thanks to Dr Takuji Sawamoto for his great help and important suggestions for our experiments and also to the following undergraduate students from the Laboratory of Soil Fertility and Plant Nutrition, Rakuno Gakuen University, for their assistance during the experiments; Mr Yoshiyuki Hara, Mr Koichi Takakura, Miss Kaori Noda and Miss Eri Ozawa.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGMENTS
  8. REFERENCES
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