Routine measurement of the soil water potential gradient near saturation using a pair of tube tensiometers

Soil Research ◽  
2001 ◽  
Vol 39 (5) ◽  
pp. 1147 ◽  
Author(s):  
P. A. Hutchinson ◽  
W. J. Bond
Keyword(s):  
Hydraulic Conductivity ◽  
Water Potential ◽  
Soil Water ◽  
Soil Water Potential ◽  
Potential Gradient ◽  
Darcy's Law ◽  
Deep Drainage ◽  
Soil Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Water Potential Gradient

We describe a new tensiometer for routine measurements of the soil water potential near saturation. The device is called the tube tensiometer because it is a long, open-topped, vertical tube (>1 m long) that is filled with porous material. The tube tensiometer has advantages over other known tensiometers as it does not require maintenance when the sensing tip dries beyond its air entry pressure and it is capable of being completely buried beyond the cultivation zone so that it does not foul tillage and harvesting equipment. The disadvantage of the tube tensiometer is that it only operates in the range of soil water potentials from –L to 0 cm of water, where L is the length of the tube tensiometer. The output from the tube tensiometer was compared with mercury tensiometers in a 120-day controlled field drainage and evaporation experiment. The regression between instruments was high (r2 = 0.99) and the accuracy of the tube tensiometer was <0.5 cm of water. The soil water potential gradient near saturation can be measured by installing a pair of vertically separated tube tensiometers. If the soil hydraulic conductivity is known then the soil water flux near saturation can be estimated using Darcy's Law. When the installation depth is below the active rooting zone of a crop then deep drainage can be estimated. This application of the tube tensiometer was demonstrated by measuring the vertical soil water potential gradient at a depth of 1 m beneath a wheat field near Harden, NSW, in response to winter rainfall. The major limitation to the use of Darcy's Law for the routine monitoring of deep drainage remains the estimation of the soil hydraulic conductivity. Ongoing work is focussing on the use of tube tensiometers to provide simultaneous measurements of both hydraulic gradient and hydraulic conductivity.

A modelling framework to predict transpiration reductions during drought based on soil hydraulics 

2021 ◽  
Author(s):  
Andrea Carminati ◽  
Mathieu Javaux
Keyword(s):  
Hydraulic Conductivity ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Soil Water ◽  
Stomatal Closure ◽  
Soil Water Potential ◽  
Soil Drying ◽  
Soil Hydraulic Conductivity ◽  
Plant Hydraulics ◽  
Soil Hydraulic

<p>There is increasing need for mechanistic and predictive models of transpiration and stomatal response to drought. Global measurements of transpiration showed that the decrease in soil moisture is a primary constrain on transpiration. Additionally, a recent meta-analysis indicated that stomatal closure is explained by the loss in soil hydraulic conductivity, more than that of the xylem. Despite these evidences on the role of soil drying as a key driver of transpiration reduction, the mechanisms by which soil drying impacts transpiration, including the effect of different soil hydraulic properties, are not fully understood.</p><p>Here, we propose that stomata regulate transpiration in such a way that the relation between transpiration and the difference in water potential between soil and leaves remains linear during soil drying and increasing vapor pressure deficit (VPD). The onset of hydraulic nonlinearity sets the maximum stomatal conductance at a given soil water potential and VPD. The resulting trajectory of the stomatal conductance for varying soil water potentials and VPD depends on soil and plant hydraulics, with the soil hydraulic conductivity and root length being the most sensitive parameters.</p><p>From this hydraulic framework it follows that stomatal closure is not simply a function of soil moisture, soil water potential or leaf water potential. Instead, it depends on transpiration demand and soil-plant hydraulics in a predictable way. The proposed concept allows to predict transpiration reductions during drought with a limited number of parameters: transpiration demand, plant hydraulic conductivity, soil hydraulic conductivity and active root length. In conclusion, this framework highlights the role of the soil hydraulic conductivity as primary constrain on transpiration, and thus on stomatal conductance and photosynthesis.</p>

scholarly journals Soil hydraulic conductivily measurement on a sloping field

2000 ◽  
Vol 4 (3) ◽  
pp. 480-482
Author(s):  
Luís Carlos Timm ◽  
Julio Cesar Martins de Oliveira ◽  
Tânia Toyomi Tominaga ◽  
Fábio Augusto Meira Cássaro ◽  
Klaus Reichardt ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water Potential ◽  
Vertical Flow ◽  
Experimental Site ◽  
Soil Hydraulic Conductivity ◽  
Soil Movement ◽  
Neutron Probe ◽  
Field Methodology ◽  
Sloping Field ◽  
Soil Hydraulic

A field methodology is presented for the measurement of the soil hydraulic conductivity in a sloping field, minimizing the leveling soil movement before water pounding and redistribution. The assurance of vertical flow only is performed through soil water potential isolines. The hydraulic conductivity was determined by the instantaneous profile method. Results for the nine neutron probe access tubes indicate that one single K(theta) relation is sufficient to represent the experimental site.

The decline in xylem flow to mango fruit at the end of its development is related to the appearance of embolism in the fruit pedicel

2015 ◽  
Vol 42 (7) ◽  
pp. 668 ◽  
Author(s):  
Thibault Nordey ◽  
Mathieu Léchaudel ◽  
Michel Génard
Keyword(s):  
Hydraulic Conductivity ◽  
Water Potential ◽  
Fruit Development ◽  
Hydraulic Properties ◽  
Potential Gradient ◽  
Mango Fruit ◽  
Xylem Flow ◽  
Water Potential Gradient ◽  
The Impact ◽  
Late Growth

The decline in xylem flow during the late growth stage in most fruits may be due either to a decrease in the water potential gradient between the stem bearing the fruit and the fruit tissues or to a decrease in the hydraulic conductivity of xylem vessels, or both. In this study, we analysed changes in xylem flows to the mango Mangifera indica L. fruit during its development to identify the sources of variation by measuring changes in the water potential gradient and in the hydraulic properties of the fruit pedicel. The variations in xylem and transpiration flows were estimated at several stages of mango fruit development from the daily changes in the fresh mass of detached and girdled fruits on branches. The water potential gradient was estimated by monitoring the diurnal water potential in the stem and fruit. The hydraulic properties of the fruit pedicel were estimated using a flow meter. The results indicated that xylem flow increased in the early stages of fruit development and decreased in the late stage. Variations in xylem flow were related to the decrease in the hydraulic conductivity of xylem vessels but not to a decrease in the water potential gradient. The hydraulic conductivity of the fruit pedicel decreased during late growth due to embolism caused by a decrease in the fruit water potential. Further studies should establish the impact of the decrease in the hydraulic conductivity of the fruit pedicel on mango growth.

Tree/pasture interactions at a range of tree densities in an agroforestry experiment. III. Water uptake in relation to soil hydraulic conductivity and rooting patterns

1990 ◽  
Vol 41 (4) ◽  
pp. 709 ◽  
Author(s):  
J Eastham ◽  
CW Rose ◽  
DM Cameron ◽  
SJ Rance ◽  
T Talsma ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Root Length ◽  
Tree Density ◽  
Soil Hydraulic Conductivity ◽  
Tree Transpiration ◽  
Rooting Patterns ◽  
Soil Hydraulic ◽  
Water Contents

Eucalyptus grandis was planted in a Nelder fan design in November 1983 into a previously established pasture dominated by Setaria sphacelata cv. Kazungula, at the CSIRO Sanford Pasture Research Station, Queensland, Australia. Nine concentric rings of 18 trees were planted at radii of 4.4-61.6 m, giving a range of tree densities which decreased from 3580 to 42 stems/ha. Tree transpiration was studied at three tree densities (2150, 304 and 82 stems/ha, representing high, medium and low densities) over a 'drought' period of approximately 1 yr (Nov. 1985-Sep. 1986) and related to rooting patterns and soil hydraulic properties. Over the range of soil water contents studied, the ratio of tree transpiration rate to equilibrium evaporation rate (T/Esub(eq)) decreased linearly with decreasing mean soil water content at each tree density. To investigate the effects of soil hydraulic conductivity and root length density on the total transpirational flux, overall soil conductances (Ksub(s)) were calculated, with soil conductance in each horizon weighted according to the length of root in that horizon. At each tree density, decreases in the ratio T/Esub(eq) were related to decreases in ln Ksub(s) measured at 1.2 m from the stem. A more rapid decrease in T/Esub(eq) with decrease in water content observed at the low tree density was attributed to a greater decrease in Ksub(s) as mean water contents decreased. The greater decrease in Ksub(s) at low tree densities was associated with a larger proportion of water extracted and a higher proportion of total root length in surface soil horizons, which showed a greater decrease in hydraulic conductivity than subsoil horizons for the same decrease in water content.

scholarly journals Assessing Water Infiltration and Soil Water Repellency in Brazilian Atlantic Forest Soils

2020 ◽  
Vol 10 (6) ◽  
pp. 1950 ◽  
Author(s):  
Sergio Esteban Lozano-Baez ◽  
Miguel Cooper ◽  
Silvio Frosini de Barros Ferraz ◽  
Ricardo Ribeiro Rodrigues ◽  
Laurent Lassabatere ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Atlantic Forest ◽  
Water Repellency ◽  
Water Infiltration ◽  
Brazilian Atlantic Forest ◽  
Soil Water Repellency ◽  
Soil Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Remnant Forest

This study presents the results of the soil hydraulic characterization performed under three land covers, namely pasture, 9-year-old restored forest, and remnant forest, in the Brazilian Atlantic Forest. Two types of infiltration tests were performed, namely tension (Mini-Disk Infiltrometer, MDI) and ponding (Beerkan) tests. MDI and Beerkan tests provided complementary information, highlighting a clear increase of the hydraulic conductivity, especially at the remnant forest plots, when moving from near-saturated to saturated conditions. In addition, measuring the unsaturated soil hydraulic conductivity with different water pressure heads allowed the estimation of the macroscopic capillary length in the field. This approach, in conjunction with Beerkan measurements, allowed the design better estimates of the saturated soil hydraulic conductivity under challenging field conditions, such as soil water repellency (SWR). This research also reports, for the first time, evidence of SWR in the Atlantic Forest, which affected the early stage of the infiltration process with more frequency in the remnant forest.

A parameterised equation to estimate soil hydraulic conductivity in the field

Soil Research ◽  
2004 ◽  
Vol 42 (3) ◽  
pp. 283 ◽  
Author(s):  
K. Reichardt ◽  
L. C. Timm ◽  
O. O. S. Bacchi ◽  
J. C. M. Oliveira ◽  
D. Dourado-Neto
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Water Dynamics ◽  
Water Drainage ◽  
Soil Water Dynamics ◽  
Soil Hydraulic Conductivity ◽  
Exponential Character ◽  
Simplifying Assumptions ◽  
Soil Hydraulic

The description of soil water dynamics using the Darcy–Buckingham approach involves the determination and use of soil hydraulic conductivity K v. soil water content θ functions. Many of the methods developed for the measurement of K are based on simplifying assumptions, such as the unit gradient and the choice of fixed models for the K(θ) relation. The need of quick, simple, and inexpensive methods to measure K(θ) in the field using a large number of replicates has also led soil physicists to develop simple methods. This paper presents a procedure that makes use of parameters of equations used to explain the internal water drainage process, and that naturally leads to the exponential character of the K(θ) relation. Results show that the parameterised equation represents a more rigorous estimation of K(θ), compared with the methods that assume unit gradient.

Libardi's method refinement for soil hydraulic conductivity measurement

Soil Research ◽  
2001 ◽  
Vol 39 (4) ◽  
pp. 851 ◽  
Author(s):  
P. L. Libardi ◽  
P. L. Libardi ◽  
K. Reichardt ◽  
K. Reichardt
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Conductivity Measurement ◽  
Soil Surface ◽  
Hydraulic Gradient ◽  
Saturated Soil ◽  
Soil Hydraulic Conductivity ◽  
Soil Hydraulic

The method of Libardi to estimate soil hydraulic conductivity in the field, during the redistribution of soil water, is discussed and improved. It is shown that if the saturated soil water content is measured at the soil surface, values at any other depth can be calculated from the database used to compute hydraulic conductivity. Since the saturated soil water content is difficult to measure and critical to the establishment of the hydraulic conductivity functions, this is an important refinement of the method. It is also shown that the unit hydraulic gradient assumption, which is part of the methodology, does not introduce significant errors in the estimation of soil hydraulic conductivity.

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