scholarly journals Carbon sequestration and selected hydraulic characteristics under conservation agriculture and traditional tillage practices in Malawi

Soil Research ◽  
2020 ◽  
Vol 58 (8) ◽  
pp. 759
Author(s):  
Pacsu L. Simwaka ◽  
Eyob H. Tesfamariam ◽  
Amos R. Ngwira ◽  
Paxie W. Chirwa
Keyword(s):  
Organic Carbon ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Particulate Organic Carbon ◽  
Hydraulic Properties ◽  
Conservation Agriculture ◽  
Sub Saharan Africa ◽  
Ecological Zones ◽  
Agro Ecological Zones

Conservation agriculture (CA) is increasingly promoted among smallholder farmers of sub-Saharan Africa in a quest to improve food security while sustaining the natural resource base of the agro-ecosystems where agriculture is based. The aim of this study was to investigate the effects of CA and traditional tillage on soil organic carbon (SOC) and selected hydraulic properties in two contrasting agro-ecological zones of Malawi. Six farmers hosted on-farm trials in each location, with each farmer having the following treatments: CA with continuous sole maize (CA-SM), CA with maize–legume intercrops (CA-ML), and traditional tillage with continuous sole maize (CT-SM). Soil samples were randomly collected in October 2015, from farmers’ fields located in Chipeni, Chinguluwe, Lemu, and Zidyana where CA had been implemented for 10 years (2005–2015) at six depth intervals: 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Bulk density, soil water characteristics, and pore size distribution were determined using undisturbed core samples. At all sites, CA improved total SOC, carbon stocks, and the stable fraction of particulate organic carbon. Maize–legume intercropping under CA had 35%, 33%, and 73% more total SOC than CT-SM in Chipeni, Lemu, and Zidyana respectively. In Chinguluwe and Lemu, CA-ML had 0.54 and 0.50 g kg–1 respectively more stable fraction of particulate organic carbon (POMP) than CT-SM; whereas in Chipeni, CA-SM had 0.73 g kg–1 higher POMP compared with CT-SM. CA also improved soil porosity, pore size distribution, and water retention capacity by increasing the proportion of mesopores and micropores compared with CT-SM. Thus, changing management practices from CT-SM to CA has the potential to improve the soil organic matter and soil hydraulic properties across agro-ecological zones in Malawi, which is important for sustainable agriculture. Farmers should be encouraged to minimise tillage, retain residues as mulch on the soil surface, and practice crop rotation.

scholarly journals Hydraulic Properties of Forest Soils with Stagnic Conditions

Forests ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1113
Author(s):  
Stefan Julich ◽  
Janis Kreiselmeier ◽  
Simon Scheibler ◽  
Rainer Petzold ◽  
Kai Schwärzel ◽  
...  
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Soil Samples ◽  
Stagnant Water ◽  
Infiltration Rates ◽  
Retention Characteristic ◽  
Water Conditions

Tree species, e.g., shallow vs. deep rooting tree species, have a distinct impact on hydrological properties and pore size distribution of soils. In our study, we determined the soil hydrologic properties and pore size distribution at three forest stands and one pasture as reference on soils with stagnant water conditions. All sites are located in the Wermsdorf Forest, where historical studies have demonstrated severe silvicultural problems associated with stagnant water in the soil. The studied stands represent different stages of forest management with a young 25-year-old oak (Sessile Oak (Quercus petraea) and Red oak (Q. robur)) plantation, a 170-year-old oak stand and a 95-year-old Norway Spruce (Picea abies) stand in second rotation. We determined the infiltration rates under saturated and near-saturated conditions with a hood-infiltrometer at the topsoil as well as the saturated hydraulic conductivity and water retention characteristic from undisturbed soil samples taken from the surface and 30 cm depth. We used the bi-modal Kosugi function to calculate the water retention characteristic and applied the normalized Young-Laplace equation to determine the pore size distribution of the soil samples. Our results show that the soils of the old stands have higher amounts of transmission pores, which lead to higher infiltration rates and conductance of water into the subsoil. Moreover, the air capacity under the old oak was highest at the surface and at 30 cm depth. There was also an observable difference between the spruce and oak regarding their contrasting root system architecture. Under the oak, higher hydraulic conductivities and air capacities were observed, which may indicate a higher and wider connected macropore system. Our results confirm other findings that higher infiltration rates due to higher abundance of macropores can be found in older forest stands. Our results also demonstrate that an adapted forest management is important, especially at sites affected by stagnant water conditions. However, more measurements are needed to expand the existing data base of soil hydraulic properties of forest soils in temperate climates.

SOIL HYDRAULIC PROPERTIES DETERMINED WITH WATER AND WITH A HYDROCARBON LIQUID

1970 ◽  
Vol 50 (1) ◽  
pp. 79-84 ◽  
Author(s):  
J. C. VAN SCHAIK
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Relative Permeability ◽  
Hydraulic Properties ◽  
Direct Transfer ◽  
Soil Hydraulic Properties ◽  
Distribution Index ◽  
Wetting Fluid ◽  
Hydrocarbon Oil

Hydraulic properties of three soils were compared using either water or a hydrocarbon oil as the wetting fluid. Equations relating various properties for oil were also valid for water when appropriate values for water were used. As differences in saturated permeability were not consistent, a direct transfer of data obtained with oil to those of water was not possible. The relative permeability for both fluids showed better agreement because bubbling pressures were similar. However, the pore-size distribution index for water was somewhat lower than that for oil.

Quantification of key factors driving the microbial metabolism in the vadose zone – A microscale-modelling perspective

2021 ◽  
Author(s):  
Amir Golparvar ◽  
Matthias Kästner ◽  
Martin Thullner
Keyword(s):  
Microbial Community ◽  
Organic Carbon ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Microbial Activity ◽  
Water Flow ◽  
Vadose Zone ◽  
Reactive Transport ◽  
Chemical Factors

<p>Organic carbon (C), either originated from soil organic carbon or introduced externally from anthropogenic sources, is the main pool for providing microorganisms with materials for biosynthesis (anabolism) and energy for catabolism. Routing the carbon source between catabolic and anabolic pathways eventually decides over the fate of C; either if it leaves the system as inorganic carbon (i.e. CO<sub>2</sub>) or, it stays in it due to anabolism and cell synthesis processes. The microbial carbon use efficiency (CUE) – and thus the proportion of the C that (potentially) remains in soil – depends on various factors.  Physio-chemical condition of the hosting environment, the composition and activity of the microbial community and in extreme cases, climatic changes can cause a high spatio-temporal variability in microbial activity and CUE. At microscale, also the pore-size distribution, pore connectivity and pore water-content can (directly or indirectly) alter the distribution of carbon and energy fluxes in soils. Across different soil types and conditions, the evolution of microbial community and of their CUE in the simultaneous presence of various factors are poorly understood.</p><p>In order to capture the in-situ dynamics of microbial activity and CUE in the dynamically changing environment of the vadose zone, we apply a pore-scale reactive transport modelling approach to disentangle the interplay of physio-chemical factors in the evolution of the soil carbon pool. Our modelling framework is capable providing a resolution of unsaturated water flow and solute transport at the microscale combined with capturing the underlying biogeochemical processes for tracking the evolution of microbial communities along with C pools in soil. Physical properties of the porous structure (such as pore geometry, pore size distribution and their connectivity) are accounted for via using digitized -CT images. Variable water flow and distribution is achieved by solving the Navier Stokes equation. A full set of advective-diffusive-reactive transport equation is solved for all chemical and microbial species to investigate their evolution in time and space. Model simulation cover various scenarios differing in properties of the solid matrix, imposed flow conditions and considered organic carbon substrates. Sensitivity simulations are performed to single out the effect of different bio-physio-chemical factors on evolution of microbial biomass and CUE.</p>

Determining pore size distribution in wet earlywood cell wall by solute exclusion using total organic carbon technique (TOC)

2014 ◽  
Vol 48 (4) ◽  
pp. 787-795 ◽  
Author(s):  
Aldo Rolleri ◽  
Francisco Burgos ◽  
Claudio Bravo-Linares ◽  
Ester Vásquez ◽  
Fernando Droppelmann
Keyword(s):  
Cell Wall ◽  
Organic Carbon ◽  
Pore Size Distribution ◽  
Total Organic Carbon ◽  
Pore Size ◽  
Size Distribution ◽  
Solute Exclusion

SOIL HYDRAULIC PROPERTIES AFFECTED BY SATURATION TECHNIQUE

1969 ◽  
Vol 49 (1) ◽  
pp. 95-102 ◽  
Author(s):  
J. C. van Schaik ◽  
G. E. Laliberte
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Atmospheric Pressure ◽  
Hydraulic Properties ◽  
Test Fluid ◽  
Soil Hydraulic Properties ◽  
Vacuum Saturation ◽  
Distribution Index ◽  
Entrapped Air

Properties characterizing the hydraulic behavior of three soils were determined from drainage cycle tests using samples wetted with core test fluid by three saturation techniques: saturation under vacuum, saturation from below at atmospheric pressure and saturation from above at atmospheric pressure. Saturated permeability and pore-size distribution index were notably less for samples saturated at atmospheric pressure than for the vacuum-saturated samples. Bubbling pressure and residual saturation, on the other hand, were not affected by saturation technique. The observed dependence of saturated permeability and pore-size distribution index on saturation technique was attributed to the effect of entrapped air. In the modeling of field problems, determining the hydraulic properties of soils wetted at atmospheric pressure is advised.

pyGAPS: A Python-Based Framework for Adsorption Isotherm Processing and Material Characterisation

2019 ◽  
Author(s):  
Paul Iacomi ◽  
Philip L. Llewellyn
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Surface Area ◽  
Isosteric Heat ◽  
Material Characterisation ◽  
Mixture Adsorption ◽  
Surface Energetics ◽  
Adsorption Processing ◽  
User Friendly

Material characterisation through adsorption is a widely-used laboratory technique. The isotherms obtained through volumetric or gravimetric experiments impart insight through their features but can also be analysed to determine material characteristics such as specific surface area, pore size distribution, surface energetics, or used for predicting mixture adsorption. The pyGAPS (python General Adsorption Processing Suite) framework was developed to address the need for high-throughput processing of such adsorption data, independent of the origin, while also being capable of presenting individual results in a user-friendly manner. It contains many common characterisation methods such as: BET and Langmuir surface area, t and α plots, pore size distribution calculations (BJH, Dollimore-Heal, Horvath-Kawazoe, DFT/NLDFT kernel fitting), isosteric heat calculations, IAST calculations, isotherm modelling and more, as well as the ability to import and store data from Excel, CSV, JSON and sqlite databases. In this work, a description of the capabilities of pyGAPS is presented. The code is then be used in two case studies: a routine characterisation of a UiO-66(Zr) sample and in the processing of an adsorption dataset of a commercial carbon (Takeda 5A) for applications in gas separation.

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