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PhD topic Oliver Larsen
of biological waste management to mitigation of climate change – a
greenhouse gas balance for composting and compost application
|Abstract:||Beside water vapor
(H2O) and carbon dioxide (CO2), the main
contributing gases to climate change are methane (CH4)
and nitrous oxide (N2O). It is a widely accepted thesis
that human activities enhance the emissions of climate changing
greenhouse gases (GHG). The atmospheric concentration of
N2O for example has increased by a factor 1.2 since
pre-industrial times (Stocker et al., 2013). According to the report
of the German national GHG inventory (Strogies and Gniffke, 2013)
N2O contributes with 6.2 % to German GHG emissions in
2011, which correlates to 57,144 Gg CO2-equivalents.
With 71 % (40,557 Gg CO2-equivalents), the main part
of German N2O emissions originated from agricultural soils
(Strogies and Gniffke, 2013). Processes in soil effecting
N2O emissions are the priming effect, nitrification and
According to Thangarajan et al. (2013) the priming effect (term suggested by Bingeman et al., 1953) describes the stimulation of soil organic decomposition by the addition of organic amendments. Thereby a change or growth in microbial activity leads to CO2, CH4 as well as N2O emissions.
Nitrification and denitrification are the two main sources for N2O. Nitrification is the oxidation of ammonium () to nitrate (). The conversion comprises several partial steps like the formation of N2O among others. Chemo-auto trophic bacteria from the species of Nitrosomonas and Nitrobacter carry out these aerobic reactions. Denitrification is the reduction of via nitrite () to gaseous nitrous oxides (NO, N2O) and molecular nitrogen (N2). The responsible species of bacteria, Pseudomonas and Alcaligenes, require low level of oxygen and easily decomposable organic substances. Whereas Nitrification is the main N2O production process in well-aerated soils in moderate climate, Denitrification mainly causes N2O emissions in humid and carbon rich soils. The presence of is the prerequisite for Nitrification and denitrification. Sources for Ammonium can be mineral fertilizers like ammonium sulfate (NH4)2SO4 or ammonium nitrate H4N2O3. (Blume et al., 2010)
Sources for Nitrogen on German agricultural soils are mainly mineral fertilizers, harvesting residues and manure with 46 %, 26 % and 21 %, respectively (Strogies and Gniffke, 2013). Ding et al. (2013) showed for maize and wheat fields in China that 74 % to 98 % of fertilizer induced N2O emissions appears short after (within two weeks) fertilization. Similarly, Vallejo et al. (2006) states that liquid fertilizers cause N2O peaks right after the fertilization, whereas N2O from solid fertilizers peaks during the first irrigation period. These numbers indicate overloads of fertilizers. It can be assumed that the buffer ability of agricultural soils is not sufficient to provide a continual release of the applied fertilizers. Additionally to the release of GHGs an intensive use of mineral fertilizer can contribute to soil degradation, damage to the environment, and loss of biodiversity (Jiang and Yan, 2010, see Thangarajan, 2013). An alternative to mineral fertilizer can be organic amendments (OA), like compost. Organic agriculture possesses several advantages such as improving plant growth and yield, soil carbon (C) content, and microbial biomass and activity, and preventing desertification by improving soil structure and fertility (Thangarajan, 2013). Furthermore a study by Franco-Otero et al. (see Thangaraja, 2013, 2012) reported that soil amended with compost from municipal solid waste (MSW) showed higher total organic C, humic acid C, fulvic acid C, water-soluble C, proteins, and available forms of P, K, Fe and Zn than the unamended soils. Additionally, the application of compost can affect GHG emissions as well. Ding et al. (2013) express that increasing soil organic carbon by adding compost to arable soils in the North China plain has the potential to reduce the amount of mineral fertilizer and mitigate N2O emissions. Other studies however reported that the application of compost enhance N2O emissions (Thangaraja, 2013).
Although there have been a few studies about the impact of compost amendment on climate change, there has been no GHG balance including both, emissions from production and emissions from application of compost. Within this thesis, the link between GHG emissions from production of compost and the potential reduction of GHG emissions from compost application on arable soils will be established. To accomplish that goal following research questions are asked:
1.1. Research question
i. To which extent does composting of organic residues contribute to the formation of GHG emissions?
ii. Does different methods of composting show different potentials of formation of GHG emissions?
iii. Which effect do different methods of compost application have on the formation of GHG from agricultural soils?
iv. What effect does the quality of the compost and the input substrate have on GHG emissions from agricultural soils? These five research questions will be answered due to conducting following research work packages:
1.2. Research work packages
i. Quantification of GHG emissions from two different composting approaches of organic municipal solid waste
ii. Investigation of the application effect of compost on agricultural soils with focus on GHG emissions
iii. Development of a GHG balance comprising the composting process and the application of the compost on agricultural soils
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