Factors affecting nitric oxide and nitrous oxide emissions from ...

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estimates from Colorado grasslands, and these are quite different to intensively developed pasture, where only one estimate was available. Global NOx budgets do confirm that the soil source of NO is similar in magnitude to fossil fuel emissions of NOx (Davidson & Kingerlee, 1997). Stehfest & Bouwman (2006) examined N2O and NO emission from agricultural fields and soils under natural vegetation, and found that on a global basis grasslands comprised almost 30% of the NO emissions from ‘agricultural fields and soils under natural vegetation’. Grazed grasslands were excluded from this most recent study due to insufficient studies and reporting of data. Given the rates of N in ruminant urine patches and the prevalence of managed grazing systems worldwide it might be expected that NO emissions from grazed grassland would make a significant contribution to the global NO budget from soils. Table 2-1 Global Inventory of NO Emissions from Soils (Davidson & Kingerlee, 1997) It is known that reactive forms of N in the atmosphere are mainly represented by oxidized N2O and NO + NO2 and reduced forms of N (NHx). The primary sources of these reactive N forms in the troposphere include fossil fuel combustion, biomass burning, lightning, soil microbial activity and transport from the stratosphere. 4
As noted in the introduction N2O is a precursor to NO formation in the stratosphere and subsequent O3 depletion, it also contributes to ca. 6% of the greenhouse gas effect. While NO is involved in production of O3 in the troposphere as noted in the introduction. These forms of N (NO and NO2) except N2O can be deposited onto terrestrial and aquatic ecosystems via dry and wet depositions causing deleterious effects on these ecosystems. These effects include soil acidification and nutrient enhancement that can lead to eutrophication of natural pristine ecosystems (Fraser & Chilvers, 1981; Holland & Lamarque, 1997; Johnson et al., 1991; Kahl et al., 1993). 2.3 Production mechanisms of NOx and N2O in soils Microbial soil processes are the dominant source of both N2O and NO in soils with nitrification, denitrification, nitrifier-denitrification and abiotic reactions all recognized as mechanisms (Firestone & Davidson, 1989; Wrage et al., 2001). Nitrification is the process where ammonia and/or nitrite (NO2 - ) are oxidised by chemoautotrophic or heterotrophic soil bacteria that use these N substrates as a primary energy source. Ammonia (NH3) is formed from the ammonium (NH4 + ) ion. The first stage in the nitrification pathway is the conversion of NH3 to hydroxylamine (NH2OH) by ammonia monooxygenase. The second reaction involves the oxidation of NH2OH to nitrite by hydroxylamine oxidoreductase via uncharacterised intermediaries. Nitric oxide has been identified as a possible oxidative intermediate (Fig. 2.1) but the exact role and nature of this process has not been conclusively demonstrated (Hooper, 1989). In the final stage of nitrification, nitrite (NO2 - ) is converted to nitrate (NO3 - ) by nitrite oxidoreductase. Ammonia oxidation is considered to be the rate limiting step for nitrification since NO2 - is rarely found to accumulate in the environment (Prosser, 1989). In high concentrations NH3 is toxic to NO2 - oxidising bacteria (Chalk & Smith, 1983). The process of ammonia oxidation leads to a net acidification of the soil (Wrage et al., 2001). In well aerated soil NO fluxes have ranged from 0.1 to 10% of the NH4 + oxidized (Anderson & Levine, 1987; Hutchinson & Brams, 1992; Poth & Focht, 1985; Veldkamp & Keller, 1997). Nitrous oxide is also formed during nitrification via the chemical decomposition of NH2OH or NO2 - , which can be considered a form of abiotic N2O production (Wrage et al., 2001). 5
Page 1 and 2: Factors affecting nitric oxide and
Page 3 and 4: In experiment two (chapter 5) the o
Page 5 and 6: Acknowledgements I am deeply thankf
Page 7 and 8: Table of Contents Abstract.........
Page 9 and 10: 6.3.7 NOx fluxes...................
Page 11 and 12: List of Tables Table 2-1 Global Inv
Page 13 and 14: Table 7-1 Mean and S.E.M of soil pH
Page 15 and 16: Figure 4.16 Initial soil pH and NH4
Page 17 and 18: Figure 5.29 Q10(5-15 o C) values fo
Page 19 and 20: Figure 7.13 Soil N2O-N fluxes over
Page 21 and 22: Chapter 1 Introduction Managed past
Page 23: 2.1 Introduction Chapter 2 Review o
Page 27 and 28: Figure 2.3 Transformation of minera
Page 29 and 30: 2.5 NOx emissions from urine patche
Page 31 and 32: emissions but not NO. This at odds
Page 33 and 34: 2.6.4 Temperature Soil temperature
Page 35 and 36: 3.1 Introduction Chapter 3 Material
Page 37 and 38: difference. The LMA-3D was also abl
Page 39 and 40: NO 2 reading on LMA-3D (ppbV) 60 50
Page 41 and 42: Concentration (NO-N g m -3 ) 20 18
Page 43 and 44: depth of 7 cm and drying them in th
Page 45: 3.9 Laboratory experiments A Paparu
Page 48 and 49: 4.2 Materials and Methods 4.2.1 Soi
Page 50 and 51: 4.3 Results 4.3.1 Soil NH4 + -N con
Page 52 and 53: NO 2 - -N (g g -1 dry soil) 5 4 3 2
Page 54 and 55: NO x-N Soil pH N 2O-N NH 4 + -N NO
Page 56 and 57: 4.3.3 Soil NO3 - -N concentrations
Page 58 and 59: Table 4-7 Net NH4 + -N depletion an
Page 60 and 61: 4.3.6 Soil surface pH After urine a
Page 62 and 63: When data were pooled over all samp
Page 64 and 65: The NO-N flux was influenced by a s
Page 66 and 67: 4.3.8.1 Net NH4 + -N depletion and
Page 68 and 69: When the mean NO-N flux rate betwee
Page 70 and 71: 4.3.9 N2O fluxes In the absence of
Page 72 and 73: The cumulative N2O emissions as a p
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µg N 2O-N g -1 soil h -1 0.025 0.0
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concentrations (Tables, 4-2 - 4-5),
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4.4 Regression analysis 4.4.1 Predi
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4.4.2 Prediction of N2O-N When log1
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Soil surface pH increases occurred
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Unlike the NO-N fluxes, which were
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optimum pH was observed for net NO-
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Future work could further examine t
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5.2 Materials and Methods 5.2.1 Tre
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NH 4 + -N (g g -1 dry soil) 1000 80
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NH 4 + -N (g g -1 dry soil) NH 4 +
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NO 2 - -N (g g -1 dry soil) 14 12 1
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NO 2 - -N (g g-1 dry soil) NO 2 - -
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Table 5-3 Pearson correlation betwe
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5.3.3 Soil NO3 - -N concentrations
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NO 3 - -N (g g -1 dry soil) NO 3 -
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Rate of depletion/accumulation (ng
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NH4 + -N:NO 3 - -N ratio 180 160 14
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Surface soil pH 8.0 7.5 7.0 6.5 6.0
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HNO 2 (ng g -1 dry soil) 60 50 40 3
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g NO-N m -2 h -1 140 120 100 80 60
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g NO-N m -2 h -1 50 40 30 20 10 0 2
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Q 10 (15-22 o C) 80 60 40 20 0 11%
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Table 5-9 Mean NO-N flux as a perce
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These treatment effects led to a si
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g N 2O-N m -2 h -1 g N 2 O-N m -2 h
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Temperature Moisture NO-N NH 4 + -N
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Temperature Moisture NO-N NH 4 + -N
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Q 10 (15-22 o C) 100 80 60 40 20 0
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N 2O-N: NO-N 500 400 300 200 100 0
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WFPS (%) 100 80 60 40 20 0 5 10 15
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Table 5-18 The results of multiple
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Table 5-19 The significance of vari
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Table 5-22 The results of multiple
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pool. For example, when averaged ov
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depletion rate, was the soil pH. It
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0.20 g H2O g -1 soil, and temperatu
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the current experimental results. U
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134
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collected from cows at the Lincoln
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NH 4 + -N (g g -1 dry soil) 1200 10
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concentrations increasing at differ
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6.3.4 Net NH4 + -N depletion and NO
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Soil pH 8.0 7.5 7.0 6.5 6.0 5.5 5.0
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6.3.7 NOx fluxes Urine-N applicatio
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Cumulative NO-N (% of urine-N appli
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6.3.7.1 NO-N flux rate as a percent
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6.3.8 N2O fluxes The mean N2O-N flu
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Cumulative N 2 O-N ( % of uine-N ap
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6.3.10 Soil WFPS Soil moisture cont
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Table 6-6 Correlation of log10NO-N
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log 10 NO-N predicted log 10 NO-N p
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6.5 Discussion 6.5.1 Soil inorganic
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The concentrations of HNO2 were thu
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% of NO 2 - -N pool beings turnedov
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6.6 Conclusions Urine-N application
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7.2 Materials and Methods 7.2.1 Fie
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7.2.4 Meteorological data and soil
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7.3.5 Soil ammonium: nitrate ratio
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treatments showed a significant eff
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7.3.7 Theoretical HNO2 concentratio
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7.3.8 Rainfall and Water Filled Por
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7.3.10 NOx fluxes The only gas dete
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7.3.12 N2O-N: NO-N ratio There were
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Table 7-3 Results of multiple regre
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Measured/Predicted NO-N flux 400 30
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The predicted NO-N fluxes were inte
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Table 7-7 Regression coefficients d
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logN 2 O-N 4 3 2 1 0 logN 2 O-N vs
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lowering of the net NH4 + -N deplet
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approximately 6 degrees , NO3 - -N
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204
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8.2 Materials and Method Materials
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8.3.4 Net NH4 + -N depletion rates
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8.3.6 Theoretical HNO2 concentratio
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8.3.8 Soil temperature Mean soil te
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8.3.10 N2O fluxes The N2O-N fluxes
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8.4 Regression analysis 8.4.1 Predi
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The rainfall was regular (after day
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days. This was considerably higher
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to be proportional to the rate of N
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9.7 Future studies The relationshi
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Bronson, K. F., Sparling, G. P., &
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Galbally, I. E. (1989). Factor cont
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Maljanen, M., Martikkala, M., Kopon
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Scholes, M. C., Martin, R., Scholes
Page 256 and 257:
Van Slyke, D. D. (1911). A method f
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