Nitrous oxide, N2O, is the third most important (in global warming terms) of the greenhouse gases, after carbon dioxide and methane. As this book describes, although it only comprises 320 parts per billion of the earth's atmosphere, it has a so-called Global Warming Potential nearly 300 times greater than that of carbon dioxide. N2O emissions are difficult to estimate, because they are predominantly biogenic in origin. The N2O is formed in soils and oceans throughout the world, by the microbial processes of nitrification and denitrification, that utilize the reactive N compounds ammonium and nitrate, respectively. These forms of nitrogen are released during the natural biogeochemical nitrogen cycle, but are also released by human activity. In fact, the quantity of these compounds entering the biosphere has virtually doubled since the beginning of the industrial age, and this increase has been matched by a corresponding increase in N2O emissions. The largest source is now agriculture, driven mainly by the use of synthetic nitrogen fertilizers. The other major diffuse source derives from release of NOx into the atmosphere from fossil fuel combustion and biomass burning, as well as ammonia from livestock manure. Some N2O also comes directly from combustion, and from two processes in the chemical industry: the production of nitric acid, and the production of adipic acid, used in nylon manufacture.Action is being taken to curb the industrial point-source emissions of N2O, but measures to limit or reduce agricultural emissions are inherently more difficult to devise. As we enter an era in which measures are being explored to reduce fossil fuel use and/or capture or sequester the CO2 emissions from the fuel, it is likely that the relative importance of N2O in the 'Kyoto basket' of greenhouse gases will increase, because comparable mitigation measures for N2O are inherently more difficult, and because expansion of the land area devoted to crops, to feed the increasing global population and to accommodate the current development of biofuels, is likely to lead to an increase in N fertilizer use, and thus N2O emission, worldwide. The aim of this book is to provide a synthesis of scientific information on the primary sources and sinks of nitrous oxide and an assessment of likely trends in atmospheric concentrations over the next century and the potential for mitigation measures.
Artificial Soil Fertilization:Crop fertilization has been called the great saviour of humanity. Aside from increasing crop yields to help feed a human population that keeps on growing it is assumed to help farmers by increasing their profits. Sadly both of these statements are false. Not only has the rates of malnutrition and famine risen but our over-use of synthetic fertilizers and pesticides has resulted in overall decreases of usable farm land.As for the myth of increased profits, the largest recuring annual expense for farmers is for synthetic fertilizers and pesticides. While there are small increases at harvest time, there is a heavy strain on the soil itself as well as on the quality of the food produced. These synthetic chemicals are absorbed by the plants which are then absorbed by us. Apart from this it takes a lot of energy/electricity to create synthetic fertilizers and pesticides so their impact on climate change is actually larger when we factor this in.Mobile/Stationary Sources of Fossil Fuel Combustion:Fossil fuel use is again a major contributor to the emissions of another greenhouse gas. When any fossil fuel is burnt it creates nitrous oxide emissions. The majority of stationary emissions of N2O come from coal fired power plants. As for mobile emissions of N2O, almost all of it comes from the passenger cars and trucks that are used to transport people and goods. This is because catalytic converters are designed to promote the emissions of N2O even though it is a powerful greenhouse gas that can trap almost 300 times more heat than CO2.Livestock Manure:Nitrous oxide is also emited when the organic nitrogen in manure and urine decomposes. So places like poultry, beef and dairy cattle farms produce significant amounts of N2O. Because of this industrialized farming practices are the most important source of N2O emissions. It would be easy to blame farmers for this current situation but consumers have to make demands on the market if there is to be any change from what has become the norm.
The key variables leading to N2O emission are well understood and have beenreviewed extensively (Davidson et al., 1993; Skiba and Smith, 2000; Smith et al.,1998). Two biological processes are the principal sources of N2O: Nitrification is anaerobic process in which ammonium (NH4) is oxidised to nitrate (NO3) (Davidson etal., 1993). Some of the NH4 is channelled into production of NO and N2O (Poth andFocht, 1985).The second process is denitrification. It is the anaerobic reduction of NO3 to N2Oand N2 (Davidson and A., 1993), through a wide range of bacteria, which are able todenitrify. The largest rates of N2O emission tend to be associated with denitrification(Skiba and Smith, 2000).
The production, consumption and transport of greenhouse gases are stronglyinfluenced by changes in soil structure (Maag et al., 1996), temperature (Skiba etal., 1998; Smith et al., 1998) and in water content (Ball et al., 1999; Dobbie andSmith, 2001; Maljanen et al., 2003). In addition, nitrogen availability (Skiba andSmith, 2000), nitrogen deposition (Kitzler et al., 2006b), soil acidity (Yamulki et al.,1997), soil organic matter (Kitzler et al., 2006a), soil microbial activity (Castro et al.,1995; Dobbie et al., 1996) and the vegetation type (Papen and Butterbach-Bahl,1999; Pilegaard et al., 2006) have a pronounced influence on various chemical,physical and biological soil properties, which lead to greenhouse gas exchange.Understandig these exchange dynamics is critical for the construction of regionaltrace gas models and for the prediction of trace gas fluxes under climate changescenarios.
Anincrease in temperature leads to an increase in the size of anaerobic zones and thusleads to an increase in the rate of denitrification (Smith et al., 2003). Highest N2Oemissions, separated by land use type, were measured at our grassland sites. Thisis supported by laboratory studies of Schaufler et Al. (2009). Most of our grasslandswere fertilized and grazed, which results in high mineral N soil content. Theavailability of mineral N as a substrate for nitrification and denitrification is anessential requirement for stimulating N2O emission (Skiba and Smith, 2000).Application of mineral N fertilisers, excreta and urine of grazing animals increasesN2O emissions very rapidly (Skiba and Smith, 2000).
Beuro of merterological research center – BMRC
N2O were marginally significantlyhigher (P50.04) in the exclusion plot prior to thestart of the exclusion treatment, and then becamesignificantly lower in the exclusion plot compared withthe control plot (Po0.01) during the wet seasons afterthe throughfall exclusion began
CLIMATE CHANGE<br />Definition:<br /> Climate change refers to a change in the state of the climate that can be identified (e.g. using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. It refers to any change in climate over time, whether due to natural variability or as a result of human activity.<br />This usage differs from that in the United Nations Framework Convention on Climate Change (UNFCCC), where climate change refers to a change of climate that is attributed directly or indirectly by human activity.<br />Source: Climate Change 2007: Synthesis Report<br />
Emissions<br />Nitrification: <br />Aerobic process in which ammonium (NH4) is oxidised to nitrate (NO3) (Davidson et al., 1993). Some of the NH4 is channelled into production of NO and N2O (Poth and Focht, 1985).<br />2. Denitrification: <br /> It is the anaerobic reduction of NO3 to N2O and N2 (Davidson and A., 1993), through a wide range of bacteria, which are able to denitrify. The largest rates of N2O emission tend to be associated with denitrification (Skiba and Smith, 2000).<br />
FINDINGS - temperature<br />The global temperature will rise upbetween 1.5 and 4.5°C, especially in the northern altitudes in comparison to the restof Europe (IPCC, 2007).<br />A laboratory investigation was performed to measure N2O fluxes from 13 Northern European soils with different land use types (cropland, forest, grassland and wetland).<br />Most Sites emission increased under increasing temperature conditions. <br />Source: Climate Change effects on greenhouse gas emissions from Northern European soils - Universität Wien 2009, <br />
FINDINGS - Temperature<br />The Pearson rank correlation demonstrates that at nine sites soil temperature has a<br />positive influence on N2O emissions with an r ranging from 0.15 to 0.45 at BE-Vie<br />and DK-RisOnly the two sites IE-Dri and RU-Fyo soil temperature has a<br />negative influence on the N2O fluxes. At the two forest sites FI-Sod and UK-Gri no<br />significant effect could be seen.<br />Statistical Correlation Test was conducted : Pearson or Spearman : correlation factors (r),significance level (p),and number of observations (n), between N2O fluxes and the independent factor soil temperature (Temp. [°C ] from 5-20°C) <br />Anincrease in temperature leads to an increase in the size of anaerobic zones and thus<br />leads to an increase in the rate of denitrification (Smith et al., 2003).<br />Source: Climate Change effects on greenhouse gas emissions from Northern European soils - Universität Wien 2009, <br />
FINDINGS - Temperature<br />Another interesting study was done by using simulated technology and market relationships governing nitrous oxide (N2O) emissions from US agriculture for the purpose of conducting policy-sensitive emissions modelling of this greenhouse gas. <br />Source: Future N2O from US agriculture: projecting effects of changing land use, agricultural technology, and climate on N2O emissions 2002<br />
FINDINGS – Soil Moisture <br />The precipitation during summer will rise in thenorthern higher latitudes of Europe in comparison to the rest of the Europe (IPCC, 2007).<br />The same study of the 13 sites of Northern Europe was extended to the change in WFPS ( water filled pore space )<br />For most of the sites emission increased with the increase in WFPS<br />Source: Climate Change effects on greenhouse gas emissions from Northern European soils - Universität Wien 2009, <br />
FINDINGS – SOIL MOISTURE<br />We observed a positive correlation of N2O with soil moisture for 11 from 13 sites. The mean correlation factor for N2O emissions ranged from 0.15, at NLCab,up to 0.46, at DK-LVa site, (Table 7). One arable soil (BE-Lon) and one forestsite (BE-Bra) showed nosignificant correlation between N2O increase andincreasing soil moisture.<br />Assoil WFPS increases, diffusion of O2 into soil aggregates will decrease and henceClimate Change effects on greenhouse gas emissions from Northern European soilsmuch of the soil will become anaerobic. This causes increased N2O emissions bydenitrification (Dobbie and Smith, 2001). <br />Source: Climate Change effects on greenhouse gas emissions from Northern European soils - Universität Wien 2009, <br />
FINDINGS – soil moisture<br />Source: Effects of an experimental drought on soil emissions of carbon dioxide, methane, nitrous oxide, and nitric oxide in a moist tropical forest<br />E R IC A. DAV IDSON et al. <br />Another interesting study was done in Amazon Basin. Where the climate change predictions are that regional climate may become drier as a result of less recirculation of water between the deforested biosphere and the atmosphere (Shukla et al., 1990; Nobre et al., 1991; Costa & Foley, 2000;Werth & Avisar, 2002).<br />The shaded regions show the periods when thethroughfall exclusion panels were in place. <br />Monthly precipitation at the study site for 1999–2002 <br />
FINDINGS – soil moisture<br />For N2O, the annual emissions from the exclusion<br />plot were about half those of the control plot, and this isa statistically significant effect of the treatment. <br />Source: Effects of an experimental drought on soil emissions of carbon dioxide, methane, nitrous oxide, and nitric oxide in a moist tropical forest<br />E R IC A. DAV IDSON et al. <br />
Findings – Soil Moisture <br />The relationship between volumetric water content of the top 30cm soil with surface fluxes <br />N2O fluxes were positively correlated with VWC. The ratio of N2O:NO fluxes was also positivelycorrelated with VWC. Similar results have been shownfor many sites, where wet conditions favour the morereduced gas, N2O, and dry conditions favour the moreoxidized gas, NO (Firestone & Davidson, 1989; Davidsonet al., 2000a; Davidson & Verchot, 2000).<br />Source: Effects of an experimental drought on soil emissions of carbon dioxide, methane, nitrous oxide, and nitric oxide in a moist tropical forest<br />E R IC A. DAV IDSON et al. <br />