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

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

<p>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.</p><p>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.</p><p>We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm³) containing a loamy sand, either with or without the introduction of a 20 µm 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 µm d<sup>-1</sup> at 20% volumetric water content.</p><p>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.</p><p>We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.</p><p> </p>

scholarly journals Impact of freeze–thaw cycles on soil structure and soil hydraulic properties

SOIL ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 179-191
Author(s):  
Frederic Leuther ◽  
Steffen Schlüter
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Structure ◽  
Hydraulic Properties ◽  
Initial Structure ◽  
Soil Hydraulic Properties ◽  
Freeze Thaw ◽  
Frost Action ◽  
Unsaturated Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
The Impact

Abstract. The ploughing of soils in autumn drastically loosens the soil structure and, at the same time, reduces its stability against external stresses. A fragmentation of these artificially produced soil clods during wintertime is often observed in areas with air temperatures fluctuating around the freezing point. From the pore perspective, it is still unclear (i) under which conditions frost action has a measurable effect on soil structure, (ii) what the impact on soil hydraulic properties is, and (iii) how many freeze–thaw cycles (FTCs) are necessary to induce soil structure changes. The aim of this study was to analyse the cumulative effects of multiple FTC on soil structure and soil hydraulic properties for two different textures and two different initial structures. A silt clay with a substantial amount of swelling clay minerals and a silty loam with fewer swell/shrink dynamics were either kept intact in undisturbed soil cores taken from the topsoil from a grassland or repacked with soil clods taken from a ploughed field nearby. FTCs were simulated under controlled conditions and changes in pore structure ≥ 48 µm were regularly recorded using X-ray µCT. After 19 FTCs, the impact on hydraulic properties were measured, and the resolution of structural characteristics were enhanced towards narrow macropores with subsamples scanned at 10 µm. The impact of FTC on soil structure was dependent on the initial structure, soil texture, and the number of FTCs. Frost action induced a consolidation of repacked soil clods, resulting in a systematic reduction in pore sizes and macropore connectivity. In contrast, the macropore systems of the undisturbed soils were only slightly affected. Independent of the initial structure, a fragmentation of soil clods and macro-aggregates larger than 0.8 to 1.2 mm increased the connectivity of pores smaller than 0.5 to 0.8 mm. The fragmentation increased the unsaturated hydraulic conductivity of all treatments by a factor of 3 in by a factor of 3 in a matrix potential range of −100 to −350 hPa, while water retention was only slightly affected for the silt clay soil. Already 2 to 5 FTCs enforced a well-connected pore system of narrow macropores in all treatments, but it was steadily improved by further FTCs. The implications of fewer FTCs during milder winters caused by global warming are twofold. In ploughed soils, the beneficial seedbed consolidation will be less intense. In grassland soils, which have reached a soil structure in dynamic equilibrium that has experienced many FTCs in the making, there is still a beneficial increase in water supply through increasing unsaturated hydraulic conductivity by continued FTCs that might also be less efficient in the future.

euptfv2: updated hydraulic pedotransfer functions for Europe

2021 ◽  
Author(s):  
Brigitta Szabó ◽  
Melanie Weynants ◽  
Tobias Weber
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Properties ◽  
Water Content ◽  
Hydraulic Properties ◽  
Field Capacity ◽  
Pedotransfer Functions ◽  
Predictor Variables ◽  
Soil Hydraulic Properties ◽  
Matric Potential ◽  
Soil Hydraulic

<p>We present improved European hydraulic pedotransfer functions (PTFs) which now use the machine learning algorithm random forest and include prediction uncertainties. The new PTFs (euptfv2) are an update of the previously published euptfv1 (Tóth et al., 2015). With the derived hydraulic PTFs soil hydraulic properties and van Genuchten-Mualem model parameters can be predicted from easily available soil properties. The updated PTFs perform significantly better than euptfv1 and are applicable for 32 predictor variables combinations. The uncertainties reflect uncertainties from the considered input data, predictors and the applied algorithm. The euptfv2 includes transfer functions to compute soil water content at saturation (0 cm matric potential head), field capacity (both -100 and -330 cm matric potential head) and wilting point (-15,000 cm matric potential head), plant available water content computed with field capacity at -100 and -330 cm matric potential head, saturated hydraulic conductivity, and Mualem-van Genuchten parameters of the moisture retention and hydraulic conductivity curves. The influence of predictor variables on predicted soil hydraulic properties is explored and suggestions to best predictor variables given.</p><p>The algorithms have been implemented in a web interface (https://ptfinterface.rissac.hu) and an R package (https://doi.org/10.5281/ZENODO.3759442) to facilitate the use of the PTFs, where the PTFs’ selection is automated based on soil properties available for the predictions and required soil hydraulic property.</p><p>The new PTFs will be applied to derive soil hydraulic properties for field- and catchment- scale hydrological modelling in European case studies of the OPTAIN project (https://www.optain.eu/). Functional evaluation of the PTFs is performed under the iAqueduct research project.</p><p> </p><p>This research has been supported by the Hungarian National Research, Development and Innovation Office (grant no. KH124765), the János Bolyai Research Scholarship of the Hungarian Academy of Sciences (grant no. BO/00088/18/4), and the German Research Foundation (grant no. SFB 1253/12017). OPTAIN is funded by the European Union’s Horizon 2020 Program for research and innovation under Grant Agreement No. 862756.</p>

scholarly journals An easily installable groundwater lysimeter to determine waterbalance components and hydraulic properties of peat soils

2003 ◽  
Vol 7 (1) ◽  
pp. 23-32 ◽  
Author(s):  
K. Schwaerzel ◽  
H. P. Bohl
Keyword(s):  
Hydraulic Conductivity ◽  
Hydraulic Properties ◽  
Capillary Flow ◽  
Soil Hydraulic Properties ◽  
Peat Soils ◽  
Simple Method ◽  
Groundwater Levels ◽  
Unsaturated Hydraulic Conductivity ◽  
Wide Range ◽  
Soil Hydraulic

Abstract. A simple method for the installation of groundwater lysimeters in peat soils was developed which reduces both time and financial effort significantly. The method was applied on several sites in the Rhinluch, a fen peat land 60 km northwest of Berlin, Germany. Over a two-year period, upward capillary flow and evapotranspiration rates under grassland with different groundwater levels were measured. The installation of tensiometers and TDR probes additionally allowed the in situ determination of the soil hydraulic properties (water retention and unsaturated hydraulic conductivity). The results of the measurements of the unsaturated hydraulic conductivity demonstrate that more than one single method has to be applied if the whole range of the conductivity function from saturation to highly unsaturated is to be covered. Measuring the unsaturated conductivity can be done only in the lab for an adequately wide range of soil moisture conditions. Keywords: peat soils, soil hydraulic properties, evapotranspiration, capillary flow, root distribution, unsaturated zone

Comparison of the Instantaneous Profile Method and inverse modelling for the prediction of effective soil hydraulic properties

Soil Research ◽  
2005 ◽  
Vol 43 (5) ◽  
pp. 599 ◽  
Author(s):  
Oagile Dikinya
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Sandy Soil ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Pressure Head ◽  
Inverse Modelling ◽  
Soil Hydraulic Properties ◽  
Loamy Soil ◽  
Soil Hydraulic

Soil hydraulic conductivity K(θ) and soil water retention θ(h) have been determined from a drainage experiment. Two lysimeters, one filled with a sandy soil and the other with a loamy soil, were set up for a 1-dimensional transient flow experiment. The data were collected after flooding the lysimeters with water. Soil water contents were measured by time domain reflectrometry (TDR) and pressure heads were measured by tensiometers with mercury manometers. The experimental data determined by the instantaneous profile method (IPM) were compared with the results obtained by inverse modelling. The inverse modelling proved to be superior to the IPM methodology in effective prediction of hydraulic properties. The measurable properties water content and pressure head were optimised for the following datasets: water content (WC), pressure head (P-h), and a combination of WC and P-h. For both soils the optimisation of the dataset with both WC and P-h resulted in parameters that corresponded closely to the soil hydraulic data generated by the IPM method. The correspondence for the water retention data was better than for the hydraulic conductivity data. The datasets with WC only or P-h only did not contain enough information to accurately estimate the soil hydraulic properties. In most cases the results indicated that the sandy soil gave better agreement than the loamy soil. This was attributed to the faster drainage of the sandy than the loamy soil.

Root effects on soil water and hydraulic properties

Biologia ◽  
2007 ◽  
Vol 62 (5) ◽  
Author(s):  
Horst Gerke ◽  
Rolf Kuchenbuch
Keyword(s):  
Soil Moisture ◽  
Moisture Content ◽  
Water Content ◽  
Bulk Density ◽  
Soil Water ◽  
Soil Water Content ◽  
Hydraulic Properties ◽  
Soil Hydraulic Properties ◽  
Soil Hydraulic ◽  
Root Effects

AbstractPlants can affect soil moisture and the soil hydraulic properties both directly by root water uptake and indirectly by modifying the soil structure. Furthermore, water in plant roots is mostly neglected when studying soil hydraulic properties. In this contribution, we analyze effects of the moisture content inside roots as compared to bulk soil moisture contents and speculate on implications of non-capillary-bound root water for determination of soil moisture and calibration of soil hydraulic properties.In a field crop of maize (Zea mays) of 75 cm row spacing, we sampled the total soil volumes of 0.7 m × 0.4 m and 0.3 m deep plots at the time of tasseling. For each of the 84 soil cubes of 10 cm edge length, root mass and length as well as moisture content and soil bulk density were determined. Roots were separated in 3 size classes for which a mean root porosity of 0.82 was obtained from the relation between root dry mass density and root bulk density using pycnometers. The spatially distributed fractions of root water contents were compared with those of the water in capillary pores of the soil matrix.Water inside roots was mostly below 2–5% of total soil water content; however, locally near the plant rows it was up to 20%. The results suggest that soil moisture in roots should be separately considered. Upon drying, the relation between the soil and root water may change towards water remaining in roots. Relations depend especially on soil water retention properties, growth stages, and root distributions. Gravimetric soil water content measurement could be misleading and TDR probes providing an integrated signal are difficult to interpret. Root effects should be more intensively studied for improved field soil water balance calculations.

Soil hydraulic properties of an Orthic Black Chernozem under long-term tillage and residue management

1996 ◽  
Vol 76 (1) ◽  
pp. 63-71 ◽  
Author(s):  
Baldev Singh ◽  
D. S. Chanasyk ◽  
W. B. McGill
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Size ◽  
Hydraulic Properties ◽  
Total Porosity ◽  
Residue Management ◽  
Soil Hydraulic Properties ◽  
Transmission Characteristics ◽  
Hordeum Vulgare L ◽  
No Till ◽  
Soil Hydraulic

The effects of tillage on soil hydraulic properties are unclear from the literature and residue effects are little reported. The hydraulic properties of an Orthic Black Chernozem under three tillage-residue systems in central Alberta — tillage with straw incorporated (till+straw) or removed (till−straw) — and no tillage with straw on the surface (no till+straw) — were studied for 2 yr. Measurements began in the 9th year of continuous barley (Hordeum vulgare L.).Plant-available water capacity differed among treatments only in the 0–2.5 cm layer, due to differences in water retention at −1500 kPa. Pore size partitioning revealed relatively high macroporosities (14–18% of total porosity) and residual porosity (34–41% of total porosity), but no treatment differences in the tillage layer. Saturated hydraulic conductivity (Ksat), infiltration rate and cumulative infiltration at 1 h followed the trend: no till+straw > till+straw > till−straw. Infiltration characteristics and hydraulic conductivity had considerable temporal variation. Interestingly, field and laboratory measurements gave the same order of magnitude of transmission characteristics. The common similarity of the no till+straw and the till+straw treatments and their usual difference from the till−straw treatment, especially in the water transmission characteristics, indicate the importance of the return of residue to the soil. The influence of straw on soil hydraulic properties does not appear to depend on whether it was incorporated or not. Key words: tillage, straw, residue, soil hydraulic properties, infiltration, pore size distribution

scholarly journals Comparison of the inverse modeling approach and traditional methods to estimate the unsaturated hydraulic properties in a sandy loam soil

2020 ◽  
Vol 34 (3) ◽  
pp. 310-324
Author(s):  
Leonardo Ezequiel Scherger ◽  
Victoria Zanello ◽  
Claudio Lexow
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Hydraulic Properties ◽  
Sandy Loam ◽  
Inverse Solution ◽  
Pedotransfer Functions ◽  
Retention Data ◽  
Soil Water Retention ◽  
Solution Approach ◽  
Soil Hydraulic

The aim of this work is to compare the use of the inverse solution approach in the estimation of soil hydraulic properties with traditional tension disk infiltrometer (TDI) data analysis, field retention data and commonly used pedotransfer functions (PTFs). Field data were collected in an experimental plot located at Bahía Blanca, Argentina. Field infiltration under saturated conditions was measured by the inverse auger hole method and infiltration under unsaturated conditions were carried out with TDI. Field retention data (θ(h)) were also collected periodically. The HYDRUS 2D/3D software was used to optimize soil hydraulic parameters by inverse solution according to TDI data. The saturated hydraulic conductivity measured by inverse auger hole method (5.53 cm.h-1) and calculated by Wooding analytical approach (5.35 cm.h-1) and inverse numerical simulations (5.36 cm.h-1) showed very close values. According to macroporosity estimates infiltrated water is mainly conducted through soils micro and mesopores.  Macropores only channeled 15.9% of total infiltrated flow.  Soil water retention curves (SWRC) predicted by PTFs did not represented correctly field retention data. The best adjustment between water content at specific pressure heads predicted by SWRCs and field measured water content was reached by the TDI inverse solution approach (RMSE: 0.050 cm3.cm-3). The inverse solution approach probed to be a simple and practical method to obtain an accurate estimate of both, SWRC and hydraulic conductivity curve.

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