scholarly journals Evaluation of denitrification and decomposition from three biogeochemical models using laboratory measurements of N<sub>2</sub>, N<sub>2</sub>O and CO<sub>2</sub>

2021 ◽  
Vol 18 (20) ◽  
pp. 5681-5697
Author(s):  
Balázs Grosz ◽  
Reinhard Well ◽  
Rene Dechow ◽  
Jan Reent Köster ◽  
Mohammad Ibrahim Khalil ◽  
...  
Keyword(s):  
Sandy Soil ◽  
Measurement Techniques ◽  
Model Complexity ◽  
Model Parameters ◽  
Silt Loam ◽  
Arable Soils ◽  
Control Factors ◽  
Biogeochemical Models ◽  
Silt Loam Soil ◽  
Loam Soil

Abstract. Biogeochemical models are essential for the prediction and management of nitrogen (N) cycling in agroecosystems, but the accuracy of the denitrification and decomposition sub-modules is critical. Current models were developed before suitable soil N2 flux data were available, which may have led to inaccuracies in how denitrification was described. New measurement techniques, using gas chromatography and isotope-ratio mass spectrometry (IRMS), have enabled the collection of more robust N2, N2O and CO2 data. We incubated two arable soils – a silt-loam and a sand soil – for 34 and 58 d, respectively, with small field-relevant changes made to control factors during this period. For the silt-loam soil, seven treatments varying in moisture, bulk density and NO3- contents were included, with temperature changing during the incubation. The sandy soil was incubated with and without incorporation of litter (ryegrass), with temperature, water content and NO3- content changing during the incubation. The denitrification and decomposition sub-modules of DeNi, Coup and DNDC were tested using the data. No systematic calibration of the model parameters was conducted since our intention was to evaluate the general model structure or “default” model runs. Measured fluxes generally responded as expected to control factors. We assessed the direction of modeled responses to control factors using three categories: no response, a response in the same direction as measurements or a response in the opposite direction to measurements. DNDC responses were 14 %, 52 % and 34 %, respectively. Coup responses were 47 %, 19 % and 34 %, respectively. DeNi responses were 0 %, 67 % and 33 %, respectively. The magnitudes of the modeled fluxes were underestimated by Coup and DNDC and overestimated by DeNi for the sandy soil, while there was no general trend for the silt-loam soil. None of the models was able to determine litter-induced decomposition correctly. To conclude, the currently used sub-modules are not able to consistently simulate the denitrification and decomposition processes. For better model evaluation and development, we need to design better experiments, take more frequent measurements, use new or updated measurement techniques, address model complexity, add missing processes to the models, calibrate denitrifier microbial dynamics, and evaluate the anaerobic soil volume concept.

scholarly journals Soil texture can predominantly control organic matter mineralization in temperate climates by regulating soil moisture rather than through direct stabilization

2021 ◽  
Author(s):  
Haichao Li ◽  
Jan Van den Bulcke ◽  
Orly Mendoza ◽  
Heleen Deroo ◽  
Geert Haesaert ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Microbial Activity ◽  
Sandy Soil ◽  
Soil Texture ◽  
Capillary Rise ◽  
Sandy Soils ◽  
Silt Loam ◽  
Silt Loam Soil ◽  
Loam Soil ◽  
Silty Soils

&lt;p&gt;Soil organic carbon (OC) levels generally increase with increasing clay and silt content under a similar climatic zone because of increased association of OC to clay minerals and stronger occlusion inside aggregates. Surprisingly though, in Western Europe many silt loam soils actually bear low topsoil OC levels compared to lighter textured soils. Soil texture obviously also strongly controls moisture availability with consequent indirect impact on heterotrophic activity. We hypothesized that with increasingly frequent summer drought: 1) soil microbial activity in sandy soils is more likely impeded due to their limited water holding capacity retention during droughts, while soil OC mineralization in silty soils remain be less drought-limited; 2) capillary rise from sufficiently shallow groundwater would, on the other hand, alleviate the water stress in lighter textures. To test these hypotheses, we established a one-year field trial with manipulation of soil texture, monitoring of soil moisture and maize-C decomposition via &lt;sup&gt;13/12&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; emissions. The upper 0.5 m soil layer was replaced by sand, sandy loam and silt loam soil with low soil OC. Another sandy soil treatment with a gravel layer was also included beneath the sand layer to exclude capillary rise. Soil texture did not affect maize-C mineralization (C&lt;sub&gt;maize&lt;/sub&gt;-min) until April 2019 and thereafter C&lt;sub&gt;maize&lt;/sub&gt;-min rates were higher in the silt loam than in the sandy soils (P=0.01). &amp;#952;&lt;sub&gt;v&lt;/sub&gt; correlated positively with the C&lt;sub&gt;maize&lt;/sub&gt;-min rate for the sand-textured soils only but not for the finer textures. These results clearly highlight that soil texture controlled C&lt;sub&gt;maize&lt;/sub&gt;-min indirectly through regulating moisture under the field conditions starting from about May, when soils faced a period of drought. By the end of the experiment, more added C&lt;sub&gt;maize&lt;/sub&gt; was mineralized in the silt loam soil (81%) (P&lt;0.05) than in the sandy soil (56%). Capillary rise did not result in a significant increase in cumulative C&lt;sub&gt;maize&lt;/sub&gt;-min in the sandy soil, seemingly because the capillary fringe did not reach the sandy topsoil layer. These results imply that, under future climate scenarios the frequency of drought is expected to increase, the largely unimpeded microbial activity in silty soils might lead to a further stronger difference in soil OC with coarser textured soils under similar management.&lt;/p&gt;

scholarly journals Evaluation of denitrification from three biogeochemical models using laboratory measurements of N<sub>2</sub>, N<sub>2</sub>O and CO<sub>2</sub>

2021 ◽  
Author(s):  
Balázs Grosz ◽  
Reinhard Well ◽  
Rene Dechow ◽  
Jan Reent Köster ◽  
M. Ibrahim Khalil ◽  
...  
Keyword(s):  
Measurement Techniques ◽  
Isotope Ratio Mass Spectrometry ◽  
Parameter Determination ◽  
Future Research ◽  
Model Parameters ◽  
Model Structure ◽  
Arable Soils ◽  
Loamy Soil ◽  
Biogeochemical Models ◽  
Induced Decomposition

Abstract. Biogeochemical models are useful for the prediction of nitrogen (N) cycling processes, but accurate description of the denitrification and decomposition sub-modules is critical. Current models were developed before suitable soil N2 flux data were available; new measurement techniques have enabled the collection of improved N2 data. We use measured data from two laboratory incubations to test the denitrification sub-modules of existing biogeochemical models. Two arable soils – a silt-loam and a sand – were incubated for 34 and 58 days, respectively. Fluxes of N2, N2O and CO2 were quantified using gas chromatography and isotope-ratio mass spectrometry (IRMS). For the loamy soil, seven moisture and three NO3− contents were included, with temperature changing during the incubation. The sandy soil was incubated with and without incorporation of litter (ryegrass), with temperature, water content and NO3− content changing during the incubation. Three common biogeochemical models (Coup, DNDC and DeNi) were tested using the data. No systematic calibration of the model parameters was conducted since our intention was to evaluate the general model structure or “default” model runs. As compared with measured fluxes, the average N2+N2O fluxes of the default runs for loamy soil were approximately 3 times higher for Deni, 105 times smaller for DNDC and 22 times smaller for Coup. For the sandy soils, default runs were 3 times higher for DeNi, 7 times smaller for DNDC and 12 times smaller for Coup. While measured fluxes were overestimated by DeNi and underestimated by DNDC and Coup, the temporal patterns of the measured and the modeled emissions were similar for the different treatments. None of the models was able to determine litter-induced decomposition correctly. The reason for the differences between the measured and modeled values can be traced back to model structure uncertainty and/or parameter uncertainty. Given the aim of our work – to assess existing model processes for further development and/or to identify missing processes within the models – these results provide valuable insights into avenues for future research. We conclude that the predicting power of the models could be improved through future experiments that collect data on denitrification activity with a concurrent focus on control parameter determination.

scholarly journals VEGETATIVE GROWTH AND NUTRIENT LEVELS OF LINGONBERRIES GROWN IN FOUR ALASKAN SUBSTRATES

1982 ◽  
Vol 62 (4) ◽  
pp. 969-977 ◽  
Author(s):  
PATRICIA S. HOLLOWAY ◽  
ROBERT M. VAN VELDHUIZEN ◽  
CECIL STUSHNOFF ◽  
DAVID K. WILDUNG
Keyword(s):  
Vegetative Growth ◽  
Sandy Loam ◽  
Leaf Size ◽  
Maximum Growth ◽  
Stem Length ◽  
Dry Matter Accumulation ◽  
Silt Loam ◽  
Tissue Samples ◽  
Silt Loam Soil ◽  
Loam Soil

Vegetative growth of lingonberries was observed on plants growing in four unsterilized, native-Alaskan substrates: coarsely-ground Lemeta peat, Fairbanks silt loam soil, a mixture of peat and silt loam soil and washed Chena very fine sandy loam soil. Following three growing seasons, plants in the peat treatment showed the greatest increase in vegetative growth as revealed by the number of new stems produced, stem length and dry weight per plant. Leaf size did not differ among substrate treatments. The leaves on plants grown in the peat substrate remained green throughout the entire experiment. The leaves of plants in all other treatments showed varying degrees of chlorosis followed by reddening and necrosis. Differences in concentration of N, P, K, Mn, Fe, Zn and Al in whole-plant tissue samples were recorded. The results indicate lingonberries should be grown in a peat substrate for maximum growth and dry matter accumulation.

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