Soil Nutrient Effects on Suction and Volumetric Water Content in Heavily Compacted Vegetated Soil

Time domain reflectometry (TDR) can be used to determine the volumetric water content of soils. This note describes the utilization of a TDR miniprobe in triaxial testing. The TDR performance was examined with a series of tests that not only proved its reliability but also resulted in two empirical correlations. Using these correlations, the degree of saturation and volumetric water content during triaxial testing could be determined. The TDR was then put to use in a laboratory program designed to investigate the response of loose gassy sand under static and cyclic loading. Because of the TDR measurements it was possible to determine the degree of saturation and void ratio of the gassy specimens. The TDR miniprobe proved to be accurate, simple to use, and inexpensive to build.Key words: time domain reflectometry, TDR, triaxial testing, gassy, unsaturated.

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Hyphal colonization of Rhizophagus irregularis increases unsaturated hydraulic conductivity of a loamy sand distant from roots

10.5194/egusphere-egu21-4564 ◽

2021 ◽

Author(s):

Michael Bitterlich ◽

Richard Pauwels

Keyword(s):

Hydraulic Conductivity ◽

Water Content ◽

Hydraulic Properties ◽

Volumetric Water Content ◽

Rhizophagus Irregularis ◽

Loamy Sand ◽

Soil Hydraulic Properties ◽

Unsaturated Hydraulic Conductivity ◽

Soil Hydraulic ◽

Root Exclusion

Hydraulic properties of mycorrhizal soils have rarely been reported and difficulties in directly assigning potential effects to hyphae of arbuscular mycorrhizal fungi (AMF) arise from other consequences of AMF being present, i.e. their influence on growth and water consumption rates of their host plants that both also influence soil hydraulic properties.We assumed that the typical nylon meshes used for root-exclusion experiments in mycorrhizal research can provide a dynamic hydraulic barrier. It is expected that the uniform pore size of the rigid meshes causes a sudden hydraulic decoupling of the enmeshed inner volume from the surrounding soil as soon as the mesh pores become air-filled. Growing plants below the soil moisture threshold for hydraulic decoupling would minimize plant-size effects on root-exclusion compartments and allow for a more direct assignment of hyphal presence to modulations in soil hydraulic properties.We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm&#179;) containing a loamy sand, either with or without the introduction of a 20 &#181;m nylon mesh equidistantly between the tensiometers. Introduction of a mesh reduced hydraulic conductivity across the soil volumes by two orders of magnitude from 471 to 6 &#181;m d-1 at 20% volumetric water content.We grew maize plants inoculated or not with Rhizophagus irregularis in the same soil in pots that contained root-exclusion compartments while maintaining 20% volumetric water content. When hyphae were present in the compartments, water potential and unsaturated hydraulic conductivity increased for a given water content compared to compartments free of hyphae. These differences increased with progressive soil drying.We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.&#160;

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Construction and calibration of TDR probes for volumetric water content estimation in a Distroferric Red Latosol

Engenharia Agrícola ◽

10.1590/s0100-69162013000500004 ◽

2013 ◽

Vol 33 (5) ◽

pp. 919-928 ◽

Cited By ~ 3

Author(s):

Rosimaldo Soncela ◽

Silvio C. Sampaio ◽

Marcio A. Vilas Boas ◽

Maria H. F. Tavares ◽

Adriana Smanhotto

Keyword(s):

Water Content ◽

Irrigation Management ◽

Time Domain Reflectometry ◽

Volumetric Water Content ◽

Coefficient Of Determination ◽

Calibration Model ◽

Advantages And Disadvantages ◽

Disturbed Soil ◽

Red Latosol ◽

The Time Domain

The determination of volumetric water content of soils is an important factor in irrigation management. Among the indirect methods for estimating, the time-domain reflectometry (TDR) technique has received a significant attention. Like any other technique, it has advantages and disadvantages, but its greatest disadvantage is the need of calibration and high cost of acquisition. The main goal of this study was to establish a calibration model for the TDR equipment, Trase System Model 6050X1, to estimate the volumetric water content in a Distroferric Red Latosol. The calibration was carried out in a laboratory with disturbed soil samples under study, packed in PVC columns of a volume of 0.0078m³. The TDR probes were handcrafted with three rods and 0.20m long. They were vertically installed in soil columns, with a total of five probes per column and sixteen columns. The weightings were carried out in a digital scale, while daily readings of dielectric constant were obtained in TDR equipment. The linear model θν = 0.0103 Ka + 0.1900 to estimate the studied volumetric water content showed an excellent coefficient of determination (0.93), enabling the use of probes in indirect estimation of soil moisture.

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Calibration of the time‐domain reflectometer and determination of the volumetric water content of the soil profile in an ultisol of Costa Rica

Communications in Soil Science and Plant Analysis ◽

10.1080/00103629609369713 ◽

1996 ◽

Vol 27 (9-10) ◽

pp. 2433-2442

Author(s):

R. Salas ◽

D. R. Bouldin ◽

E. Molina

Keyword(s):

Costa Rica ◽

Water Content ◽

Time Domain ◽

Soil Profile ◽

Volumetric Water Content ◽

The Time Domain ◽

Time Domain Reflectometer

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Experimental study on dual capillary barrier using recycled asphalt pavement materials

Canadian Geotechnical Journal ◽

10.1139/cgj-2013-0432 ◽

2014 ◽

Vol 51 (10) ◽

pp. 1165-1177 ◽

Cited By ~ 18

Author(s):

F.R. Harnas ◽

H. Rahardjo ◽

E.C. Leong ◽

J.Y. Wang

Keyword(s):

Water Content ◽

Pore Water Pressure ◽

Water Pressure ◽

Water Storage ◽

Pressure Head ◽

Volumetric Water Content ◽

Capillary Barrier ◽

Recycled Asphalt ◽

Fine Grained ◽

Drainage Rate

The performance of a capillary barrier cover as a cover system is affected by the ability of the capillary barrier to store water. To increase the water storage of a capillary barrier cover, the dual capillary barrier (DCB) concept is proposed. The objective of this paper is to investigate the water storage of the proposed DCB as compared to the storage of a traditional single capillary barrier (SCB). The investigation is conducted using two one-dimensional infiltration column tests under different rainfall conditions. The results show that a DCB stores more water as compared to SCB. The results show that the fine-grained layers of a DCB have higher volumetric water contents during drainage as compared to that of the fine-grained layer of an SCB. The higher volumetric water content is caused by the fact that the thickness of the layers in a DCB corresponds to a pore-water pressure head range where the material has the highest volumetric water content. In addition, a slower drainage rate is resulted from additional layering in a DCB.

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