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| Titel |
Fertilizer impact on biogenic nitric oxide emissions from agricultural soils of the Taklimakan desert (Xinjiang, China) |
| VerfasserIn |
A. D. Fechner, T. Behrendt, M. Bruse, B. Mamtimin, M. O. Andreae, F. X. Meixner |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068745
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| Zusammenfassung |
| It is known that soil microbial processes play a crucial role in the production and
consumption of atmospheric trace gases worldwide. Soils are mostly a major source of
biogenic nitric oxide (NO). The main influencing factors controlling soil NO emissions are
soil moisture, soil temperature, as well as nutrient availability.
Adding fertilizer to agricultural soils changes the pool of nutrients and impacts the net
NO emission from these soils. Irrigated and fertilized oases around the great Central Asian
Taklamakan desert form the backbone of the agricultural output (80% of the Chinese cotton
production) of the Xinjiang Uygur Autonomous Region (NW-China). While nowadays 90%
of the agricultural output is produced on just 4.3% of Xinjiang’s total area, recent and future
enlargement of farmland and intensification of agriculture will definitely impact the
regional soil NO emission and consequently the budget of nitrogen oxides and
ozone.
We present a systematic laboratory study of the influence of urea (CH4N2O) and
diammonium hydrogen phosphate ((NH4)2HPO4, DAP) fertilizer on NO emissions from
Xinjiang soil samples. Urea is the most widely and excessively applied fertilizer in Xinjiang.
Typically, about 600 kg ha-1 yr-1(in terms of mass of nitrogen) were applied to a cotton
field in four separate events. In the laboratory, the fertilizer was applied accordingly, ranging
from one quarter of the field amount within one of the four events (i.e. 37.5 kg ha-1 yr-1) to
quadruple of that (150 kg ha-1 yr-1). Two different measurement series have been
performed on six sub- samples (each out of a total of three soil samples taken in Xinjiang):
the first series was conducted solely with urea fertilizer, the second one with a mixture of urea
and DAP (2:1).
All sub-samples were prepared in a standardized way: a fixed mass of soil (~0.06 kg,
dried in field) was sieved (2 mm) and stored at 4Ë C. Then it was wetted up to a soil moisture
tension of 1.8Â pF. Subsequently, fertilizer was added and the experiments were started
immediately, without any pre-incubation in a dynamic chamber system (6 individual
chambers under controlled incubation conditions). Measurements were performed at
alternating soil temperature levels, switching between 20Ë C and 30Ë C after every 6
chamber cycle. To inhibit fast drying of the soil, moist air (RH~80%) was used for flushing
the chambers. Only towards the end of each experiment relative humidity of the flushing flow
was gradually reduced to zero (computer controlled) to dry out each soil sample
completely.
The experiments clearly demonstrated that the use of fertilizer causes significant changes
of biogenic NO soil emissions. It seems that depending on the initial nutrient content of the
soil, an addition of ammonium based fertilizer (urea) may increase or decrease net NO
release rates. While addition of urea to soils with an already high initial nutrient content lead
to a decrease, addition to soils of low initial nutrient content lead to an increase of net NO
emission. After reaching a critical – most likely toxic – level of nutrient content in the soil,
the addition of even more ammonium based fertilizer causes a decline of net NO
emission. There is strong indication that the use of urea and DAP mixtures may lead to
lower gaseous loss of nitrogen to the atmosphere than by application of urea alone. |
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