Begum, Shamim Ara

De Neve, Stefaan

Kader, Mohammed Abdul

Sleutel, Steven

English

Ghent University Academic Bibliography

Geophysical Research AbstractsVol. 15, EGU2013-1317, 2013EGU General Assembly 2013© Author(s) 2012. CC Attribution 3.0 License.Anaerobic N mineralization in paddy soils in relation to inundationmanagement, physicochemical soil fractions, mineralogy and soilpropertiesSteven Sleutel (1), Mohammed Abdul Kader (2), Shamim Ara Begum (2), and Stefaan De Neve (1)(1) Ghent University, Department of Soil Management, Ghent, Belgium (steven.sleutel@UGent.be), (2) BangladeshAgricultural University, Department of Soil Science, Mymenshing, BangladeshAnaerobic N mineralization measured from (saturated) repacked soil cores from 25 paddy fields in Bangladeshand was previously found to negatively related to soil N content on a relative basis. This suggests that other factorslike soil organic matter (SOM) quality or abiotic factors instead control the anaerobic N mineralization process.We therefore assessed different physical and chemical fractions of SOM, management factors and various soilproperties as predictors for the net anaerobic N mineralization.1◦ First, we assessed routinely analyzed soil parameters (soil N and soil organic carbon, texture, pH, oxalate-and pyrophosphate-extractable Fe, Al, and Mn, fixed-NH4 content). We found no significant influences of neithersoil mineralogy nor the annual length of inundation on soil N mineralization. The anaerobic N mineralizationcorrelated positively with Na-pyrophosphate-extractable Fe and negatively with pH (both at P<0.01). At this stageit is, however, not known if these relations between net evolution of NH4 and pH and Fe content are causal orindirect.2◦ Second, the 25 samples collected from farmers’ fields were physically fractionated into particulate OM andsilt and clay associated OM. The silt and clay sized OM was further chemically fractionated by oxidation with6%NaOCl to isolate an oxidation-resistant OM fraction, followed by extraction of mineral bound OM with10%HF thereby isolating the HF-resistant OM. None of the physicochemical SOM fractions were found usefulpredictors anaerobic N mineralization. The linkage between these chemical soil N fractions and N supplyingprocesses actually occurring in the soil thus appears to be weak. Regardless, we hypothesize that variation instrength of N-mineral and N-OM linkages is likely to explain variation in bio-availability of organic N andproneness to mineralization. Yet, in order to separate kinetically different soil N fractions we then postulated thatan alternative approach would be required, which instead isolates soil N fractions on the basis of bonding strength.In this respect bonding strength should be seen as opposite of proneness to dissolution of released N into water,the habitat of soil microorganisms mediating soil N mineralization. We hypothesize that soil N extracted by waterat increasing temperatures would reflect such N fractions with increasing bonding strength, in turn equivalent todecreasing bio-availability. Although water has frequently been used to extract labile SOM, its use has mostlybeen limited to 100◦C.3◦ Third we developed sub critical water extraction (SCWE) at 100◦C, 150◦C and 200◦C to isolate SOM fractionsfrom the set of 25 paddy soil samples. In all cases, SCWE organic carbon (SCWE-OC) and N (SCWE-N) in-creased exponentially with the increase of temperature. SCWE preferentially extracted N over OC with increasingtemperature. The efficiency of SCWE and the selectivity towards N were both lower in soils with increasingly reac-tive clay mineralogy. No correlations were found between the SCWE fractions and anaerobic N mineralization rate.In conclusion, SOM quantity and SOM quality, here represented by C and N distribution over physico-chemical fractions, don’t seem to dominantly determine anaerobic N mineralization in primarily young floodplainpaddy soils. Other factors with exceeding control (pH and pyrophosphate extractable Fe) appear to exist. Possibly,the specific young genesis stage of most of the soils included (termed ‘floodplain’ soils) results in a limitedavailability of readily reducible Fe. Being an important alternative electron acceptor under submerged conditions,the availability of Fe, which is also controlled by pH, may be a bottleneck in the anaerobic N mineralizationprocess. This needs to be further investigated by controlled incubation experiments with detailed follow-up of pH,redox potential, Fe in solution and mineral N.

Anaerobic N mineralization in paddy soils in relation to inundation management, physicochemical soil fractions, mineralogy and soil properties

https://biblio.ugent.be/publication/4082229/file/4087654

Anaerobic N mineralization in paddy soils in relation to inundation management, physicochemical soil fractions, mineralogy and soil properties

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