Benedikt Klein, 16.4.2012
Journal of Plant Nutrition and Soil Science
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Mineralization of nitrogen and N losses by denitrification in a soil incubation
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experiment as related to the aggregate sizes, soil temperatures and water
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contents
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Introduction:
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The use of nitrogen fertiliser for agricultural production brings two bad effects for the
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environment: First the enrichment of nitrate in soak- and ground water (Heyder et al.
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1993), second the emission of N2 and N2O through nitrification- and denitrification
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processes. Nitrous oxide is in consequence of its stability harmful to the climate. It
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reaches the stratosphere without any problems and supports the ozone depletion
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(Conrad, 1990, Braun et al., 1994). Nitrous oxide is about 310-times more harmful
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then the greenhouse gas CO2 (IPCC, 1995). Since the beginning of industrialization
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until now the N2O level rose from 270 ppb to 319 ppb (UNFCCC, 2008).
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Only one-third of nitrogen from nitrogen fertiliser which is used for agriculture
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production accumulates in plants, the rest remains unaffected in soil. The annual
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surplus amounts up to 100 kg N/ha (Nieder et al. 2007). This nitrogen surplus could
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easily be used during denitrification or accumulate in soak- and ground water.
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Globally, the loss of nitrogen is considered up to 107-161 Mio t N per year during
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denitrification (N2 and N2O) and 18-33 Mio. t N per year by eluviation (Heyder,
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1993).
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Not only the amount of N-fertiliser contributes to the loss of Nitrogen throughout
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denitrification, but also important is the type of tillage. Seiler and Conrad (1980)
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stated that application of nitrogen fertiliser always provokes bring a positive effect on
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denitrification (Seiler & Conrad, 1980), but other factors like, dryness or low
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temperatures decrease the process of denitrification (Mengel, 1982). A high activity
Benedikt Klein, 16.4.2012
Journal of Plant Nutrition and Soil Science
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of soil microbes depends on the aggregate size, there is more microbe activity in
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small than in big aggregates once (Albers B.P., 1993).
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Up to 70 % of N2O-emission come from the microbiological processes of nitrification
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and denitrification (Oenema et al., 2001).
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Nitrification benefits from high oxygen concentrations, a soil water level of pF 2.7, a
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neutral pH and moderate temperatures (20-25°C). However, denitrification is
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favoured by anaerobic conditions, high temperatures (over 25°C, minimum 0-5°C),
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high water content as well as high levels of nitrate and organic components. The
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effect of high- temperature and soil water levels on denitrification is well documented
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(Beck, 1979, Abou-Seada, 1986).
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With this background, the presented paper describes the dependence of high
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temperature and soil water as a function of the microbe activity in small aggregates
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(2 mm). With this knowledge, the loss of nitrogen and the N-mineralization is
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expected to be considerably lower in small soil aggregates than in the bigger ones. It
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should be shown that the influence of small aggregates on lowering the nitrogen loss
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by denitrification is an important factor maybe more important than only the effect of
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high- water and temperature levels.