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Keywords:

  • farmyard manure;
  • fertilizer;
  • grassland;
  • methane;
  • nitrous oxide

Abstract

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

We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N2O) and methane (CH4) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha−1 year−1. In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha−1 year−1 was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N2O and CH4 fluxes using closed chambers. Annual N2O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha−1, respectively. Annual N2O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to N2O emissions following manure application. N2O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), inline image concentration in the soil (R = 0.67, P < 0.001), soil pH (R = –0.46, P < 0.001) and inline image concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: inline image concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 0.26, P < 0.001). Annual CH4 emissions from the manure and fertilizer plots ranged from –0.74 to –0.16 and from –0.84 to –0.52 kg C ha−1, respectively. No significant difference was observed in annual CH4 emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH4 emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH4 fluxes were correlated with inline image concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P < 0.05), both inline image concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.


INTRODUCTION

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

Nitrous oxide (N2O) and methane (CH4) are important greenhouse gases that contribute to the anticipated global warming (Mosier 1998). N2O also contributes to the destruction of the stratospheric ozone (O3); however, CH4 reduces the rate at which O3 is destroyed by chloride radicals (Cicerone 1987).

In grassland soils, N2O is produced as a by-product and an intermediate of microbial nitrification and denitrification processes, respectively. Therefore, N fertilizer (Akiyama et al. 2006; Mosier et al. 1991), slurry (Christensen 1983; Glatzel and Stahr 2001), farmyard manure (Chadwick et al. 2000; Watanabe et al. 1997) and forage crop residue (Baggs et al. 2000; Mori et al. 2007) could be sources of N2O. Important environmental factors that control N2O emission are fertilization, soil moisture, soil temperature, soluble organic C in the soil and soil pH (Bouwman 1996; Davidson 1991; Maag and Vinther 1996; Mosier 1998; Yamulki et al. 1997). Manure application supplies easily degradable C compounds, a suitable nitrifiable N source and moisture to the soil, which makes conditions more favorable for nitrification and denitrification (Chadwick et al. 2000). Furthermore, after manure application, microbial activity is enhanced and oxygen (O2) is consumed, thereby allowing anaerobic sites to develop (Akiyama et al. 2004). As a result, manure application has increased N2O emission from grassland soil (Jones et al. 2005; Mosier 1998).

With respect to CH4, both emission and consumption have been observed from grassland soil (Hu et al. 2001; Kammann et al. 2001; Minami and Kimura 1993). It is important to note that the CH4 flux observed from the soil surface is defined as the net positive flux from soil to the atmosphere. Nitrogen fertilizer has reduced CH4 consumption in the soil (Hu et al. 2002; Jensen and Olsen 1998; Mosier et al. 1991); however, manure has not altered CH4 consumption in the soil (Hütsch et al. 1993). Important environmental factors that control CH4 oxidation are fertilization, soil moisture, soil temperature and soil pH (Amaral et al. 1998; Castro et al. 1995; Dunfield et al. 1993; Mori et al. 2005; Whalen and Reeburgh 1996). Slurry applied on grassland surfaces releases CH4 into the atmosphere and most of the CH4 emitted is derived from the slurry itself (Chadwick and Pain 1997). Ambient air temperature and rainfall are likely to be the most important factors controlling CH4 emission from excreta deposited by grazing animals (Yamulki et al. 1999). However, slurry application has not significantly affected annual CH4 emission from grassland soil (Glatzel and Stahr 2001).

To maintain productive swards, manure and fertilizer application is essential. In Japan, however, little information is available on the long-term effects of manure or fertilizer application on N2O and CH4 fluxes from grasslands. Furthermore, manure management methods, the timing of manure application and climatic conditions during and after manure or fertilizer application vary widely among countries and regions. In Japan, bark and sawdust are often added to cattle manure in its composting process and grasslands receive manure in late autumn to make enough space for the next manure management in the following winter. In the present study, to examine how the application of dairy cattle bark compost in late autumn affects the exchange of N2O and CH4 between grassland soil and the atmosphere, these fluxes were measured from a manure + fertilizer applied plot and a fertilizer-only applied plot over a 2-year period. We also attempted to explain the relationship between N2O and CH4 fluxes and the associated soil and environmental parameters.

MATERIALS AND METHODS

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

Site description

A field study was carried out on grassland plots located at the National Institute of Livestock and Grassland Science in Nasu, Japan (latitude 36°55′N, longitude 139°55′E). The site has an elevation of 320 m a.s.l. and is located on the border where cultivated land transitions to forest area. The dominant plant species were orchardgrass (Dactylis glomerata L.) and Italian ryegrass (Lolium multiflorum Lam.). The soil was derived from volcanic ash; Kurashima et al. (1993) previously classified it as Entic Haplumbrepts, loamy over fragmental, mixed, mesic (Soil Survey Staff 1999). The soil surface was covered with grass litter approximately 5 mm thick. The Ap horizon was observed in the 0–25 cm layer and roots were densely distributed in the 0–5 cm layer. The ground water level was at least 23 m below the soil surface. The 30-year averages for precipitation and temperature were 1,561 mm year−1 and 12.0°C, respectively (National Grassland Research Institute 2001).

Field management

The manure plot (2.3 ha) and the fertilizer plot (2.4 ha) were laid out side by side. The soil surface of both plots was mostly horizontal. Both plots had previously received N fertilizer (200 kg N ha−1 year−1) and were harvested three to four times per year before the initiation of the present study. In the manure plot, the sum of N estimated to be mineralized from the cattle manure and N applied as ammonium sulfate was adjusted to 210 kg N ha−1 year−1 (Table 1). In the fertilizer plot, 210 kg N ha−1 year−1 was applied as ammonium sulfate (Table 1). In both plots, six subplots (5 m × 5 m) were established and treated precisely for gas flux measurement. In 2004, manure (15 Mg ha−1 dairy cattle bark compost; C/N 25, total N 5.0 g kg−1 and 69% moisture) was applied to the manure plot on 10 November (Table 2). In 2005, chemical fertilizer was applied to the manure and fertilizer plots on 15 March, 26 May, 19 July and 15 September, and sward was harvested on 16 May, 11 July, 12 September and 21 November. In 2005, manure (30 Mg ha−1 dairy cattle bark compost; C/N 19, total N 6.1 g kg−1 and 68% moisture) was applied to the manure plot on 28 November (Table 2). In 2006, chemical fertilizer was applied to the manure and fertilizer plots on 16 March, 25 May, 20 July and 8 September, and sward was harvested on 21 May, 14 July, 1 September and 8 November. Nitrogen mineralization from the cattle manure was estimated based on Uchida's model (Shiga et al. 1985). According to this model, the cumulative N mineralization rate (1 – yt) was estimated to be 0.132 in the applied year (t = 1) and 0.202 the following year (t = 2), respectively. The equation is as follows:

Table 1.  Nutrient inputs to the plots from fertilizer and manure during the first year from 9 November 2004 to 8 November 2005 and the second year 9 November 2005 to 8 November 2006
PlotFertilizer application rates (kg ha−1)Mineralization from manure applied on 10 November 2004 (kg ha−1 year−1)Annual input (kg ha−1 year−1)
15 Mar.26 May19 Jul.15 Sep.
FertilizerN60606030210
P2O560303015135
K2O60606030210
ManureN50606030  9.9210
P2O550252512.5 23.4136
K2O50 0 00165215
PlotFertilizer application rates (kg ha−1)Mineralization from manure applied on 10 November 2004 and 28 November 2005 (kg ha−1 year−1)Annual input (kg ha−1 year−1)
16 Mar.25 May20 Jul.8 Sep.
  • N based on Uchida's estimation and PK based on fertilizer recommendations for Hokkaido prefecture.

FertilizerN60606030210
P2O530303015105
K2O60606030210
ManureN30606030 29.4209
P2O512.3524.724.712.35 65.7140
K2O 0 0 0 0269269
Table 2.  Properties of the manure and nutrient mineralization from the manure
Date of application10 November 200428 November 2005
  1. N, P and K mineralization in the second year is the sum of their mineralization from the manure applied on 10 November 2004 and 28 November 2005. FW, fresh weight.

Application rate (Mg ha−1 year−1) 15 30
Moisture (%) 69 68
Total N (g N kg FW−1)  5.0  6.1
Total P (g P2O5 kg FW−1)  7.8  9.0
Total K (g K2O kg FW−1) 15.7 11.7
C/N ratio 25 19
Total N in the applied manure (kg N ha−1 year−1) 75183
N mineralization in the first year (kg N ha−1 year−1)  9.9
N mineralization in the second year (kg N ha−1 year−1)  5.3 24.2
Total P in the applied manure (kg P2O5 ha−1 year−1)117270
P mineralization in the first year (kg P2O5 ha−1 year−1) 23.4
P mineralization in the second year (kg P2O5 ha−1 year−1) 11.7 54.0
Total K in the applied manure (kg K2O ha−1 year−1)236351
K mineralization in the 1st year (kg K2O ha−1 year−1)165
K mineralization in the 2nd year (kg K2O ha−1 year−1) 24246
  • yt = a × 0.01t + c × 0.63t + f × 0.955t

where yt is the rate of N remaining in the manure t years after application, t is the years after manure application (inclusive of the applied year), a, c and f are the rates of organic matter fractions with different decomposition rates (a + c + f = 1). In the case of cattle manure, a, c and f were estimated to be 0.04, 0.15 and 0.81, respectively. Therefore, annual N mineralization rates in the applied year and the following year were estimated to be 13.2% and 7.0%, respectively. Phosphorus and K mineralization from the manure were estimated based on the Handbook of Animal Waste Management and Utilization in Hokkaido 2004 (Hokkaido Prefectural Experiment Stations and Hokkaido Animal Research Center 2004), namely 20% of P and 70% of K are available in the applied year, 10% of P and 10% of K are available the following year, respectively. The manure was obtained from a commercial farm located next to our institute. Nitrogen, P and K fertilizers were applied in the form of ammonium sulfate, superphosphate and potassium sulfate, respectively.

Flux measurement

From November 2004 to November 2006, N2O and CH4 fluxes were determined using a vented closed chamber (Toma and Hatano 2007). In each subplot, a cylindrical chamber (40 cm in diameter, 30 cm in height) was inserted to a depth of 3 cm in the soil. Air (20 mL) within the chamber headspace was drawn using a plastic syringe and stored in a glass vial (10 mL). Air samples were collected from each chamber at 0 and 30 min after the chambers were set up. N2O and CH4 fluxes were calculated from the linear increase in N2O and CH4 concentration over 30 min. Measurements were carried out between 08:00 hours and 11:00 hours to minimize diurnal variation. Cumulative N2O and CH4 emissions were calculated by trapezoidal integration. The equation is as follows:

  • image

where Tn is the cumulative N2O or CH4 emission (kg ha−1period−1), ti is the time at the ith observation (h) and fi is the N2O or CH4 flux at the ith observation (µg m−2 h−1).

Gas analyses

The N2O concentration was determined using a gas chromatograph equipped with an electron capture detector (GC-14B, Porapak Q column; Shimadzu, Kyoto, Japan). The oven and detector temperatures were 80 and 340°C, respectively. The CH4 concentration was determined using a gas chromatograph equipped with a flame ionization detector (GC-8A, molecular sieve 5A column; Shimadzu). The oven and detector temperatures were 70 and 200°C, respectively. These analyses were carried out at the Laboratory of Soil Science, Hokkaido University, Sapporo, Japan, within 1 week.

Soil physical analyses

Intact soil samples were collected from the 0–5 cm layer using 100-mL stainless steel cores (DIK-1801; Daiki, Saitama, Japan). Soil bulk density was determined gravimetrically after the core samples were dried at 105°C for 24 h. Soil moisture in the 0–10 cm layer was monitored using a time domain reflectometry probe (Trime-IT; IMKO, Ettlingen, Germany). Soil moisture content was recalculated using the calibration for Andosol (Hatano et al. 1995). The equation is as follows:

  • θg = 0.9454 × θv + 0.1168

where θv is the time domain reflectrometry device reading (m3 m−3) and θg is the soil moisture content (m3 m−3). Soil temperature at 5 and 10 cm below the surface was monitored using a digital thermometer (PC-2200; Sato, Tokyo, Japan).

Soil chemical analyses

Soil samples were collected from the 0–5 cm layer every one to three flux measurements, sieved through a 2-mm mesh and bulked sufficiently from 10 cores. Subsamples (7.5 g) were extracted with 50 mL of 2 mol L−1 KCl solution or 50 mL of distilled water for analysis of inline image or inline image, respectively, followed by filtration (Whatman No. 6 filter paper; Advantec, Tokyo, Japan). The filtered extracts were kept frozen until colorimetric analysis (FIAstar 5000; Foss Tecator, Höganäs, Sweden). Subsamples (7.5 g) were shaken with 25 mL of distilled water and the pH (H2O) was determined using a pH meter (F-22; Horiba, Kyoto, Japan). Total C and N contents in the soil sampled in November 2004 were determined using a CN analyzer (JM1000CN; J-Science, Kyoto, Japan).

Precipitation

Precipitation data were obtained from meteorological observations made at the National Institute of Livestock and Grassland Science in Nasu, Japan.

Statistical analyses

Statistical analyses were conducted with Statistica 6.1 for Windows (StatSoft, Tulsa, OK, USA). A Mann–Whitney U-test was used to compare N2O fluxes, CH4 fluxes and soil environmental parameters between the plots. An anova was used to detect the quantitative relationship between treatments, years, growing periods and cumulative N2O or CH4 fluxes. Spearman's rank correlation coefficients (Spearman's R) were calculated between the mean of N2O fluxes from the six chambers and the following variables: soil moisture content, soil temperature, inline image and inline image content in the soil and soil pH. Pearson's correlation coefficients (Pearson's R) were calculated between the mean of CH4 fluxes from the six chambers and the abovementioned variables. Multiple regression analysis was carried out between the mean of N2O or CH4 fluxes from the six chambers and the following variables: soil moisture content, soil temperature, inline image and inline image content in the soil and soil pH. The forward stepwise selection was used to select predictor variables. Each variable was considered to be significant when F > 2.

RESULTS

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

Temporal change in N2O flux and annual N2O flux

The N2O flux from the manure and fertilizer plots ranged from 1 to 1,464 and from 2 to 1,226 µg N2O-N m−2 h−1, respectively (Fig. 1a). In November 2004, N2O flux increased (715 µg N2O-N m−2 h−1) just after a rainfall event (8 mm day−1) observed 2 days after manure application (Fig. 1h). In November 2005, N2O flux increased (1,464 µg N2O-N m−2 h−1) just after rainfall (6.5 and 1.5 mm day−1) was observed 5 and 6 days after manure application. In the winter period from November to March, inclusive of this manure application, cumulative fluxes were greater from the manure plot than from the fertilizer plot (Fig. 2, P < 0.001). In the other grass-growing periods, fluxes increased following fertilizer application and reached a maximum in the third grass-growing period. However, no significant difference was observed in cumulative fluxes in each grass-growing period between the plots. In the winter period, cumulative N2O fluxes were greater in 2005 than in 2004 (P < 0.001). In the first grass-growing period, cumulative N2O fluxes were greater in 2005 than in 2006 (P < 0.001). In the second and fourth grass-growing periods, cumulative N2O fluxes were greater in 2006 than in 2005 (P < 0.001 and P < 0.01, respectively). However, in the third grass-growing period there was no significant difference between 2005 and 2006.

image

Figure 1. Temporal changes in (a) N2O flux, (b) CH4 flux, (c) soil moisture, (d) soil temperature at a depth of 10 cm, (e) NH4+, (f) NO3, (g) pH (H2O) and (h) precipitation. Error bars indicate standard deviations (n = 6 for a, b, c and d; n = 3 for e, f and g). *P < 0.05. The arrows indicate the timing of the manure (M) or fertilizer (F) application.

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image

Figure 2. Cumulative N2O emission in the winter and grass-growing periods. Error bars indicate standard deviations (n = 6). *P < 0.05; **P < 0.01.

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Annual N2O emissions from the manure plot were greater than those from the fertilizer plot (Tables 3,4, P < 0.05). Annual N2O emissions from 9 November 2005 to 8 November 2006 were greater than those from 9 November 2004 to 8 November 2005 (Tables 3,4, P < 0.001).

Table 3.  Annual N2O and CH4 emissions
 PlotFirst year (9 Nov. 2004–8 Nov. 2005)Second year (9 Nov. 2005–8 Nov. 2006)
  1. Mean ± standard deviation (n = 6).

N2O (kg N ha−1 year−1)(kg N ha−1 year−1)
Manure7.0 ± 2.811.0 ± 3.6
Fertilizer4.7 ± 1.09.1 ± 2.2
CH4 (kg C ha−1 year−1)(kg C ha−1 year−1)
Manure–0.74 ± 0.32–0.16 ± 0.48
Fertilizer–0.84 ± 0.33–0.52 ± 0.25
Table 4. anova for cumulative N2O emissions
FactordfSSMSFP
  1. df, degrees of freedom; SS, sum of squares; MS, mean square; F, F ratio.

Plot15.105.075.700.019
Year120.320.322.8< 0.001
Period413233.137.2< 0.001
Plot × year10.100.070.080.779
Plot × period410.12.532.840.028
Year × period423.55.876.60< 0.001
Plot × year × period47.101.782.000.100

Temporal change in CH4 flux and annual CH4 flux

The CH4 flux from the manure and fertilizer plots ranged from –32 to 29 and from –34 to 21 µg CH4-C m−2 h−1, respectively (Fig. 1b). It is important to note that negative fluxes mean CH4 consumption in the soil. In 2004, CH4 flux increased following rainfall (8 mm day−1) observed 2 days after manure application (Fig. 1h); however, the CH4 flux was relatively small (20 µg CH4-C m−2 h−1). In 2005, a slight increase was observed in CH4 flux following manure application. In the other grass-growing periods, CH4 flux temporally increased following fertilization and decreased thereafter. Heavy rainfall also increased CH4 flux. In the second and third grass-growing periods, following fertilization, CH4 flux from the manure plot increased in comparison with the fertilizer plot. In the third grass-growing period from July to September, the cumulative CH4 fluxes were greater from the manure plot than from the fertilizer plot (Fig. 3, P < 0.05). In the other periods, however, no significant difference was observed in cumulative CH4 fluxes between the plots. In the second grass-growing period, cumulative CH4 fluxes were greater in 2006 than in 2005 (P < 0.05).

image

Figure 3. Cumulative CH4 emission in the winter and grass-growing periods. Error bars indicate standard deviations (n = 6). *P < 0.05; **P < 0.01.

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No significant difference was observed in annual CH4 emissions between the plots (Tables 3,5). Annual CH4 emissions from 9 November 2005 to 8 November 2006 were greater than from 9 November 2004 to 8 November 2005 (Tables 3,5, P < 0.01).

Table 5. anova for cumulative CH4 emissions
FactordfSSMSFP
  1. df, degrees of freedom; SS, sum of squares; MS, mean square; F, F ratio.

Plot10.0630.0632.370.127
Year10.2800.28010.50.002
Period40.1230.0311.150.337
Plot × year10.0170.0170.640.427
Plot × period40.0670.0170.620.646
Year × period40.1080.0271.010.406
Plot × year × period40.0530.0130.490.740

Soil and climatic parameters

Soil moisture content tended to be greater in the soil of the manure plot than in the soil of the fertilizer plot (Fig. 1c). The soil surface was mostly horizontal in both plots. No significant difference was observed in the soil bulk density of the plots (Table 6).

Table 6.  Soil properties in the experimental plots
PlotBulk density (Mg m−3)Total C content (g C kg−1)Total N content (g N kg−1)C/N ratio
  1. n = 6 for bulk density and n = 3 for total C and N contents and C/N ratio.

Manure0.97 ± 0.074.1 ± 0.30.34 ± 0.0212 ± 0
Fertilizer1.02 ± 0.153.3 ± 0.60.27 ± 0.0412 ± 1

From November to March, the soil temperature at a depth of 10 cm from the soil surface tended to be higher in the soil of the manure plot than in the soil of the fertilizer plot (Fig. 1d). From June to September, however, the soil temperature tended to be higher in the soil of the fertilizer plot than in the soil of the manure plot. The maximum difference in soil temperature between the plots was 1.3–1.5°C. In 2005, the highest and lowest soil temperatures were recorded on 13 January and 5 August, respectively. In 2006, the highest and lowest soil temperatures were recorded on 12 January and 18 August, respectively.

The concentration of inline image and inline image tended to be greater in the soil of the manure plot than in the soil of the fertilizer plot (Fig. 1e,f). This tendency could be attributed to N mineralization from the manure and the inorganic N initially contained in the manure itself. There are only a few exceptions, namely the inline image concentration on 2 June 2006 and the inline image concentration on 21 October 2005 and 2 June and 3 August 2006. In the first grass-growing period, the rate of N application as ammonium sulfate was greater in the fertilizer plot than in the manure plot (Table 1a,b). Nevertheless, the concentration of inline image and inline image in the soil of the manure plot seemed to be greater than in the soil of the fertilizer plot. inline image and inline image concentration in the soil increased within 2 weeks after fertilization and decreased quickly thereafter in both plots. In the second and third grass-growing periods of 2006, however, a negligible increase was observed in the inline image concentration in the soil of the manure plot. No significant differences were observed in the total C and total N contents in the soil or in the C/N ratio between the plots (Table 6).

From November 2004 to November 2005, the soil pH values of the manure plot tended to be lower than those of the fertilizer plot; however, from November 2005 to November 2006, the soil pH values of the manure plot tended to be higher than those of the fertilizer plot (Fig. 1g). In other words, over the 2 years, the soil pH values of the manure plot increased in comparison with those of the fertilizer plot. This trend could be attributed to soil acidification following the application of ammonium sulfate, the high pH of the manure itself and the K, Ca and Mg released from the decomposing manure. This trend could be attributed to the soil acidification following ammonium sulfate application, the high pH of manure itself and the potassium, calcium and magnesium released from the decomposing manure, because the amount of ammonium sulfate application in the manure plot was less than that in the fertilizer plot and manure was only applied to the manure plot.

In the winter period of 2004, and the first, second, third and fourth grass-growing periods of 2005, 186, 135, 303, 810 and 170 mm of rain fell, respectively (Fig. 1h). In the winter period of 2005, and the first, second, third and fourth grass-growing periods of 2006, 149, 213, 428, 390 and 477 mm of rain fell, respectively.

Regression analyses

The N2O fluxes were correlated with soil temperature, inline image concentration in the soil, soil pH and inline image concentration in the soil (Table 7). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: inline image concentration in the soil, soil temperature and soil moisture content (Table 8). Furthermore, in each grass-growing period except for the winter period, precipitation within 10 days after fertilization was correlated with the ratio [N2O-N emission in each grass-growing period]/[N applied as (NH4)2SO4] (Fig. 4). The CH4 fluxes were correlated with inline image concentration in the soil and soil moisture content (Table 7). When included in the multiple regression model (R = 0.29, P < 0.05), both inline image concentration in the soil and soil moisture content were significant (Table 9).

Table 7.  Correlation coefficients between N2O fluxes, CH4 fluxes and soil environmental parameters
 MoistureTemperatureinline imageinline imagepH (H2O) 
  • *

    P < 0.05;

  • **

    P < 0.01;

  • ***

    P < 0.001 (n = 98).

N2O–0.020.70***0.67***0.40***–0.46***Spearman's R
CH4 0.20*0.020.21*–0.060.09Pearson's R
Table 8.  Coefficients of multiple regression analysis for N2O fluxes (µg N2O-N m−2 h−1)
FactorStandardized coefficient βUnstandardized coefficientP
βSD
  1. n = 98; R = 0.72; SD, standard deviation.

inline image (mg N kg−1)0.52   6.70  0.95< 0.001
Temperature (°C)0.36  10.1  2.1< 0.001
Moisture (m3 m−3)0.261077299< 0.001
image

Figure 4. Relationship between the precipitation in 10 days after fertilization and the ratio of [N2O-N emission in each grass-growing period]/[N applied as (NH4)2SO4]. N2O emissions in the winter period were excluded.

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Table 9.  Coefficients of multiple regression analysis for CH4 fluxes (µg CH4-C m−2 h−1)
FactorStandardized coefficient βUnstandardized coefficientP
βSD
  1. n = 98; R = 0.29; SD, standard deviation.

inline image (mg N kg−1)0.200.1100.0530.04
Moisture (m3 m−3)0.2034.817.10.04

DISCUSSION

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

Farmyard manure application increased the annual N2O emission from grassland. This result could be attributed to N2O emission in the winter period following manure application (Figs 1a,2). A small amount of N2O was emitted immediately after manure application; however, N2O emission increased following rainfall after the manure application. The manure contained inorganic N and moisture just after its application. Therefore, the rainfall may have promoted N2O production in the manure itself or in the surface soil. The easily degradable C already present in the manure may have fuelled denitrification to a great extent (Chadwick et al. 2000). In addition, when manure was applied in late autumn, less N uptake by forage crops could have further promoted N2O production. To make the best use of N in organic manure, application should be as close as possible to the time of active crop growth when N demand is greatest (Department for Environment, Food and Rural Affairs 2001). This is particularly true for manure with a high readily available N content (e.g. slurry or poultry manure). In the present study, dairy cattle bark compost was applied and usually contains low available N. Nevertheless, high N2O emission was observed following manure application, contributing greatly to annual N2O emission (Fig. 2).

In the third grass-growing period, the high soil moisture and temperature conditions may have promoted manure decomposition (Fig. 1c,d); however, no significant difference was observed in cumulative N2O emission between the plots (Fig. 2). Even after fertilizer application, when inorganic N concentration in the soil and N2O flux simultaneously increased (Fig. 1e,f), no significant difference was observed in N2O flux between the plots. One possible explanation for this result is that the decomposition of the manure was relatively slow because of the high C/N ratio. Toma and Hatano (2007) demonstrated that the ratio of [N2O-N emission]/[N applied as various crop residues] ranged from –0.43 to 0.86% and was negatively correlated with the C/N ratio. N2O emission from manure applied to grassland may vary with animal type because differences in diet, feed conversion and manure management will result in differences in manure composition (Chadwick et al. 2000). Akiyama and Tsuruta (2003) reported that only 0.08 and 0.05% of applied N was converted to N2O from high C/N organic fertilizers, namely dried cattle manure (C/N: 24.3) and sawdust containing cattle manure (C/N: 15.9), respectively. When manure is continuously applied for many years, however, its application could increase N2O emission in the third grass-growing period. In addition, manure application on the soil surface might change the moisture and temperature conditions in the surface soil (Fig. 1c,d). In the present study, however, it was unclear whether the differences in the soil moisture and soil temperature of the plots resulted from manure application. Therefore, further extended observation is required to understand how continuous manure application affects N2O emission.

In the second and fourth grass-growing periods, N application as ammonium sulfate was the same in 2005 and 2006 (Table 1a,b). Nevertheless, cumulative N2O emissions in these grass-growing periods were greater in 2006 than in 2005 (Fig. 2). This inter-annual difference in cumulative N2O emissions in each grass-growing period could be attributed to the rainfall pattern (Fig. 1h). In 2005, precipitation was concentrated in the third grass-growing period. In 2006, however, precipitation was more evenly distributed throughout the year; some rainfall was coincidently observed following fertilization and the soil moisture content increased just after fertilization (Fig. 1c). The precipitation within 10 days after fertilization correlated with the ratio [N2O-N emission]/[N applied as (NH4)2SO4] in each grass-growing period (Fig. 4), suggesting that N2O production occurred shortly after the rainfall and significantly increased N2O emission derived from N fertilizer. Diffusion of N2O produced in the soil is suppressed following rainfall because soil water regulates aeration in the soil. In addition, N2O is easily soluble in soil water (0.64 mL mL−1) and may be stored for a while in the soil solution (Glatzel and Stahr 2001). Therefore, there is a time lag between N2O production and following N2O diffusion. In the present study, N2O fluxes generally peaked within approximately 10 days after fertilization. The soil moisture content ranged from 0.40 to 0.65 m3 m−3 (Fig. 1c), corresponding to a range of 65 to 105% water-filled pore space; therefore, denitrification could be the predominant source of N2O (Davidson 1991).

The result of the multiple regression analysis for N2O flux suggests that the high soil temperature in summer promoted microbial N2O production when inline image concentration in the soil increased just after fertilizer application (Table 8). Furthermore, soil moisture was another important factor regulating N2O emission from soil.

In our previous report, annual N2O emissions observed from other unfertilized grassland plots at our institute ranged from 0.39 to 1.59 kg N2O-N ha−1 year−1 (Mori et al. 2005). The non-leguminous grassland plot emitted only 0.39 kg N2O-N ha−1 year−1. Therefore, in the present study, most N2O emission could be derived from the manure and the fertilizer applied during the study.

Both negative and positive CH4 fluxes were observed from both plots (Fig. 1b). Therefore, CH4 flux could be the result of CH4 oxidation and CH4 production. In the winter period of 2004, CH4 flux was positive following rainfall (8 mm day−1) observed 2 days after manure application (Fig. 1h), suggesting that the rainfall could develop anaerobic microsites in the manure itself or in the surface soil and consequently CH4 was produced. Chadwick and Pain (1997) suggested that CH4 emission from manure with high dry-matter content was unaffected by soil type because the manure did not infiltrate into the soil. In the present study, the dry-matter content of the manure was quite high (31–32%). Therefore, rainfall may have partly leached easily degradable C already contained in the manure into the soil. As a result, microbial respiration of organic C may regulate O2 supply in the manure itself or in the surface soil and consequently CH4 may be produced in the manure itself or in the surface soil. However, the observed CH4 emission was quite small with a negligible contribution to annual CH4 emission (Fig. 3). This result agrees well with previously reported results in slurry-applied grassland (Glatzel and Stahr 2001).

In the third grass-growing period, manure application increased cumulative CH4 emissions (Fig. 3). In the fertilizer plot, cumulative CH4 emissions were negative. In the manure plot, however, cumulative CH4 emissions were not significantly different from zero. One possible explanation for this result is that, in the manure decomposing process, soil microorganisms lowered the O2 concentration in the surface soil and consequently reduced the CH4 oxidation rate in the surface soil. Oxygen is essential for microbial CH4 oxidation; therefore, O2 concentration controls the CH4 oxidation rate in the soil (Schnell and King 1995). CH4 production from easily degradable C compounds released from the decomposing manure is another explanation.

The result of the multiple regression analysis for CH4 flux suggests that inline image in the soil and soil moisture could have inhibited CH4 oxidation in the soil (Table 9). This result is in line with previously reported results for grasslands and forests (Jensen and Olsen 1998; Morishita et al. 2004; Mosier et al. 1991). In the third grass-growing period, inline image concentration tended to be greater in the soil of the manure plot than in the soil of the fertilizer plot (Fig. 1e). Therefore, inline image released from the decomposing manure could reduce the CH4 oxidation rate in the soil.

In our previous report, annual CH4 emissions observed from other unfertilized grassland plots at our institute ranged from –2.4 to –1.8 kg CH4-C ha−1 year−1 (Mori et al. 2005). In the present study, CH4 flux tended to increase temporally following fertilization (Fig. 1b); therefore, inline image supplemented from ammonium sulfate could have inhibited CH4 oxidation in the soil. In addition, the moisture content in the soil (Fig. 1c) was slightly greater than that in the previous report (Mori et al. 2005). Therefore, this difference in annual CH4 emission could be attributed to fertilization and aeration in the soil.

In the second grass-growing period, cumulative CH4 fluxes were greater in 2006 than in 2005 (Fig. 3, P < 0.05). This inter-annual difference in cumulative CH4 emissions in this grass-growing period could be attributed to the rainfall pattern (Fig. 1h). During the second grass-growing period much more precipitation was observed in 2006 than in 2005. This difference in rainfall was obviously reflected in the soil moisture content during this period (Fig. 1c) and consequently soil moisture controls CH4 and O2 diffusion by regulating soil aeration (Mori et al. 2005).

Conclusions

Manure application increased the annual N2O emission from grassland. The N2O emission observed following the manure application contributed to the annual N2O emission. inline image concentration in the soil, soil temperature and soil moisture were the main factors controlling N2O flux. CH4 emission following manure application was negligible and annual CH4 emission was not affected by manure application. inline image in the soil exhibited a weakly positive correlation with CH4 fluxes. Rainfall pattern was another important factor controlling inter-annual variation in cumulative N2O and CH4 fluxes from grassland.

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 thank the Racing and Livestock Association for providing the funds for this research project (GHGG-Japan). We also thank the Japan Grassland Agriculture and Forage Seed Association for organizing this research project. We thank Dr Osamu Imura, National Institute of Lifestock and Grassland Science (NILGS), for his valuable comments on the statistical analyses.

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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