Assessing Gas Diffusion Coefficients in Growing Media from in situ Water Flow and Storage Measurements

Large-sized particles (coarse peat, bark or sawdust) are often added to growing media to improve substrate aeration properties (gas storage and exchange). Recent studies have shown that large fragments mixed with fines may create barriers that restrict gas diffusion or create competition for oxygen even if they improve air storage. An experiment was carried out to compare the growth performances of growing media containing large fragments and to assess their aeration status using different methods. Different mixes were made of a fine sphagnum peat (average size 2.4 mm) and a coarse (1-2, 2-4, 4-6, 6-10, and 10-20 mm particles) sphagnum peat or bark (2-4 and 10-20 mm). These substrates had different aeration properties and were used to grow Poinsettia and Impatiens ‘New Guinea’ in a greenhouse, resulting in differences in plant growth. The results show that air-filled porosity remained relatively unaffected by fragment size. Gas relative diffusivity differed significantly between treatments and was highest in the mix with the 2-4 mm particles and diminished rapidly as fragment size increased from 4 to 20 mm or decreased to 1-2 mm. Diffusivity was clearly lower in the bark/peat mixes but showed the same trend with coarse fragments. Root and shoot growth parameters were significantly and positively correlated to gas relative diffusivity. Moreover, the growth reduction observed in the bark/peat mixes relative to pure peat was most likely linked to limited gas exchange. Air-filled porosity assessments performed in situ (in the pot itself) or prior to potting, in cylinders, gave inconsistent results or were not significantly correlated to plant growth, indicating that aeration limitations are better diagnosed with gas diffusivity in growing media.Key words: Air-filled porosity, gas relative diffusivity, gas diffusion, peat substrates, bark, Euphorbia pulcherima, Impatiens (× novae-guinea)

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The simultaneous determination of air permeability and gas diffusion through ice layers in the field

Hydrology Research ◽

10.2166/nh.2007.008 ◽

2007 ◽

Vol 38 (3) ◽

pp. 203-210 ◽

Cited By ~ 2

Author(s):

G. Fortin ◽

E. van Bochove ◽

H.G. Jones ◽

G. Thériault ◽

M. Bernier

Keyword(s):

Diffusion Coefficients ◽

Gas Diffusion ◽

Air Permeability ◽

Structural Variations ◽

Compacted Soil ◽

Gas Chamber ◽

And Diffusion ◽

Sequential Measurements

A coupled air permeameter–gas chamber has been used to measure both the air permeability and diffusion coefficient of an inert gas through natural ice layers. The apparatus was designed to take sequential measurements of both these parameters for the same sample without any intermediate manipulation of the specimen. In avoiding manipulation, errors related to the structural variations between different replicates are eliminated. The apparatus is portable, allowing measurements to be made directly at the study site. The permeability is directly measured in situ by the air permeameter while gas samples used in the diffusion experiments are collected and subsequently analysed at the laboratory. The validation of the apparatus was accomplished by comparing theoretical values for the permeability of beds of spherical beads with known dimensions. Measured permeability values,for different ice samples vary from 0.005 × 10−10 to 12.9 × 10−10 m2. Mean diffusion coefficients ranged from 0.013 to 0.028 cm2 s−1. These values are situated in the range for those found between hard packed snow and loose compacted soil.

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Electrokinetic and in situ spectroscopic investigations of CO electrochemical reduction on copper

Nature Communications ◽

10.1038/s41467-021-23582-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jing Li ◽

Xiaoxia Chang ◽

Haochen Zhang ◽

Arnav S. Malkani ◽

Mu-jeng Cheng ◽

...

Keyword(s):

Mass Transport ◽

Active Sites ◽

Gas Diffusion ◽

Reduction Reaction ◽

Adsorbed Hydrogen ◽

Diffusion Type ◽

Proton Coupled Electron Transfer ◽

Alkaline Electrolytes ◽

Reaction Orders

AbstractRigorous electrokinetic results are key to understanding the reaction mechanisms in the electrochemical CO reduction reaction (CORR), however, most reported results are compromised by the CO mass transport limitation. In this work, we determined mass transport-free CORR kinetics by employing a gas-diffusion type electrode and identified dependence of catalyst surface speciation on the electrolyte pH using in-situ surface enhanced vibrational spectroscopies. Based on the measured Tafel slopes and reaction orders, we demonstrate that the formation rates of C2+ products are most likely limited by the dimerization of CO adsorbate. CH4 production is limited by the CO hydrogenation step via a proton coupled electron transfer and a chemical hydrogenation step of CO by adsorbed hydrogen atom in weakly (7 < pH < 11) and strongly (pH > 11) alkaline electrolytes, respectively. Further, CH4 and C2+ products are likely formed on distinct types of active sites.

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Effects of processing, moisture, and storage length on the fermentation profile, particle size, and ruminal disappearance of reconstituted corn grain

Journal of Animal Science ◽

10.1093/jas/skaa332 ◽

2020 ◽

Vol 98 (11) ◽

Author(s):

Ana L M Gomes ◽

Antonio V I Bueno ◽

Fernando A Jacovaci ◽

Guilherme Donadel ◽

Luiz F Ferraretto ◽

...

Keyword(s):

Particle Size ◽

Lactic Acid ◽

Butyric Acid ◽

Hammer Mill ◽

Moisture Concentration ◽

Fermentation Profile ◽

And Storage ◽

Ground Corn ◽

Corn Grain

Abstract Our objective was to examine the effects of processing, moisture, and anaerobic storage length of reconstituted corn grain (RCG) on the fermentation profile, geometric mean particle size (GMPS), and ruminal dry matter disappearance (DMD). Dry corn kernels were ground (hammer mill, 5-mm screen) or rolled, then rehydrated to 30%, 35%, or 40% moisture, and stored for 0, 14, 30, 60, 90, 120, or 180 d in laboratory silos. Rolled corn had an increased GMPS compared with ground corn (2.24 and 1.13 mm, respectively, at ensiling). However, there was a trend for an interaction between processing and moisture concentration to affect particle size, with GMPS increasing with increased moisture concentration, especially in ground corn. Longer storage periods also slightly increased GMPS. Processing, moisture, and storage length interacted to affect the fermentation pattern (two- or three-way interactions). Overall, pH decreased, whereas lactic acid, acetic acid, ethanol, and NH3-N increased with storage length. RCG with 30% moisture had less lactic acid than corn with 35% and 40% moisture, indicating that fermentation might have been curtailed and also due to the clostridial fermentation that converts lactic acid to butyric acid. Ensiling reconstituted ground corn with 30% of moisture led to greater concentrations of ethanol and butyric acid, resulting in greater DM loss than grain rehydrated to 35% or 40% of moisture. Ammonia-N and in situ ruminal DMD were highest for reconstituted ground corn with 35% or 40% of moisture, mainly after 60 d of storage. Therefore, longer storage periods and greater moisture contents did not offset the negative effect of greater particle size on the in situ ruminal DMD of rolled RCG. Nonetheless, RCG should be ensiled with more than 30% moisture and stored for at least 2 mo to improve the ruminal DMD and reduce the formation of ethanol and butyric acid.

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