Methane oxidation in arable soil as inhibited by ammonium, nitrite, and organic manure with respect to soil pH |
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Authors: | B W Hütsch |
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Institution: | (1) Institute of Plant Nutrition, Justus-Liebig-University, Südanlage 6, D-35390 Giessen, Germany Fax: +49-641-99-39169, DE |
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Abstract: | The effects of inorganic N and organic manure, applied to a loamy arable soil, on CH4 oxidation were investigated in laboratory incubation experiments. Applications (40 mg N kg–1) of NH4Cl, (NH4)2SO4, and urea caused strong instantaneous inhibition of CH4 oxidation by 96%, 80%, and 84%, respectively. After nitrification of the added N the inhibitory effect was not fully reversible,
resulting in an residual inhibition of 21%, 16%, and 25% in the NH4Cl, (NH4)2SO4, and urea treatments, respectively. With large NH4
+ applications 240 mg N kg–1 as (NH4)2SO4] the residual inhibition was as high as 64%. Exogenous NO2
– (40 mg NO2
–-N kg–1) initially inhibited CH4 oxidation by 84%, decreasing to 41% after its oxidation. Therefore, applied NO2
– was a more effective inhibitor of CH4 consumption than NH4
+. Temporary accumulation of NO2
– during nitrification of added N was small (maximum: 1.9 mg NO2
–-N kg–1) and thus of minor importance with respect to the persistent inhibition after NH4
+ or urea application. CH4 oxidation after NaNO3 (40 mg N kg–1) and NaCl addition did not differ to that of the untreated soil. The effect of organic manures on CH4 oxidation depended on their C/N ratio: fresh sugar beet leaves enhanced mineralization, which caused an instantaneous 20%
inhibition, whereas after wheat straw application available soil N was rapidly immobilized and no effect on CH4 oxidation was found. The 28% increase in CH4 oxidation after biowaste compost application was not related to its C/N ratio and was probably the result of an inoculation
with methanotrophic bacteria. Only with high NH4
+ application rates (240 mg N kg–1) could the persistent inhibitory effect partly be attributed to a pH decrease during nitrification. The exact reason for
the observed persistent inhibition after a single, moderate NH4
+ or urea application is still unknown and merits further study.
Received: 31 October 1997 |
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Keywords: | Methane oxidation Ammonium Soil pH Nitrite Organic manure |
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