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Rainer Horn - One of the best experts on this subject based on the ideXlab platform.
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Determination of critical soil water content and Matric Potential for wind erosion
Journal of Soils and Sediments, 2011Co-Authors: Kristine Bolte, Peter Hartmann, Heiner Fleige, Rainer HornAbstract:Purpose Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θ_crit.) for deflation was extended to include Matric Potential (Ψ_crit.) as well. The focus of this paper is to quantify the Θ_crit. and Ψ_crit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψ_crit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height. Materials and methods The influence of soil water content and Matric Potential upon wind erosion was tested under wind tunnel conditions. Both were investigated in N = 49 wind tunnel experiments for a sandy Podzol topsoil from north-western Germany under a typical, constant free-stream velocity of 6.8 m s^−1. The surface (0–0.2 cm) water content was measured using a microwave sensor; Matric Potential at 0.5 cm depth was measured by laboratory tensiometer and sediment discharge was measured by modified Wilson and Cooke and combined suspended sediment traps and saltiphone. The superficial (0–0.2 cm) Matric Potential cannot be measured directly and was thus modelled using a van Genuchten retention curve model. Results and discussion The range of Θ_crit. was determined to be between 4.9 and 4.0 wt.% at the soil surface; the Ψ_crit. ranged from −75 to −43 kPa at a depth of 0.5 cm. Modelled Matric Potential at the soil surface resulted in lower values between −1.3 and −2.3 MPa as a consequence of steep gradients within soil layers. The reduction of the Θ_crit. and Ψ_crit. led to a steeply significant, almost 20-fold increase in soil losses, projected at 0.56 up to 11.00 Mg ha^−1 h^−1. The ranges of Θ_crit. and Ψ_crit. were ensured by both statistical ascertainment and impulse detection method for validation. The latter yields the specific process-based Θ_crit. and Ψ_crit. at the initiation of erosion and is hence considered the more precise threshold parameter. The impracticability of measuring the soil surface Matric Potential directly requires its modelling or derivation from measurement of relative humidity—which is only applicable for soils in equilibrium with atmospheric humidity. The modelled Matric Potentials are much lower compared to those measured at 0.5 cm depth in consequence of steep gradients within soil layers. Erosion data derived by wind tunnel experiments are not directly comparable to field data, as the wind tunnel device facilitates neither the avalanching process nor the development of a flow saturated with sediment amongst others. Discrepancies of measured sediment discharge compared to those in the literature are most of all attributable to a different reference surface area of erosion in wind tunnel experiments. Conclusions Wind tunnel experiments showed that the initiation of wind erosion can be attributed to certain ranges of Θ_crit. and Ψ_crit.. Specifying the interparticle (capillary) forces Ψ_m provides a precise parameter for describing soil strength. The Ψ_m can be regulated by conservation tillage. Measurements of soil sediment discharge at typical Θ and wind velocity indicate that the sandur plains in north-western Germany are endangered by wind erosion. Besides the regulation of soil moisture and Matric Potential, conservation soil management or the installation of shelter belts and hedges increase the overall surface roughness across various scales and hence reduce the wind erosion risk.
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Determination of critical soil water content and Matric Potential for wind erosion
Journal of Soils and Sediments, 2010Co-Authors: Kristine Bolte, Peter Hartmann, Heiner Fleige, Rainer HornAbstract:Purpose Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θcrit.) for deflation was extended to include Matric Potential (Ψcrit.) as well. The focus of this paper is to quantify the Θcrit. and Ψcrit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψcrit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height.
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Microtensiometer technique for in situ measurement of soil Matric Potential and root water extraction from a sandy soil
Plant and Soil, 1993Co-Authors: Doris Vetterlein, Horst Marschner, Rainer HornAbstract:The suitability of microtensiometers to measure the spatial variation of soil Matric Potential and its diurnal change was tested in a pot experiment with pearl millet (Pennisetum americanum [L.] Leeke) in a sandy soil as the soil dried out.
William R. Whalley - One of the best experts on this subject based on the ideXlab platform.
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Estimating penetrometer resistance and Matric Potential from the velocities of shear and compression waves
Soil Science Society of America Journal, 2013Co-Authors: Weida Gao, M. Jenkins, Chris W. Watts, Tao Ren, Ho-chul Shin, Shahram Taherzadeh, Keith Attenborough, William R. WhalleyAbstract:Recently there has been interest in using the velocity of elastic waves to deduce soil physical properties. We wanted to validate the suggestion that the small strain shear modulus has a relatively simple linear relationship with penetrometer resistance. We were also interested in testing published equations for predicting shear wave velocity with an independent data set. Three soils were investigated in this study: a loamy sand soil and two silty clay loam soils. The soils were packed into cores with vertical axial stresses of 30, 200, or 1000 kPa. Following saturation, they were drained to a range of Matric Potentials between −10 and −500 kPa. After equilibration, we measured the velocities of shear (S wave) and compression (P wave) waves as well as the penetrometer resistances. Our data confirmed a previous proposal that the penetrometer resistance was an approximately linear function of the small strain shear modulus but tested the relationship by direct measurement. The relationships were found to have some sensitivity to soil type. Nevertheless, we show for the first time that there is considerable Potential for using S wave velocity to deduce penetrometer resistance with a calibration that is relatively insensitive to soil type. Although estimation of the Matric Potential with either shear or compression wave velocity was found not to be very accurate, the possibility for estimating the Matric Potential from an elastic wave velocity given a priori knowledge of the void ratio is an interesting opportunity.
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Measurement of the Matric Potential of soil water in the rhizosphere
Journal of experimental botany, 2013Co-Authors: William R. Whalley, Eric S. Ober, M. JenkinsAbstract:The availability of soil water, and the ability of plants to extract it, are important variables in plant research. The Matric Potential has been a useful way to describe water status in a soil-plant system. In soil it is the Potential that is derived from the surface tension of water menisci between soil particles. The magnitude of Matric Potential depends on the soil water content, the size of the soil pores, the surface properties of the soil particles, and the surface tension of the soil water. Of all the measures of soil water, Matric Potential is perhaps the most useful for plant scientists. In this review, the relationship between Matric Potential and soil water content is explored. It is shown that for any given soil type, this relationship is not unique and therefore both soil water content and Matric Potential need to be measured for the soil water status to be fully described. However, in comparison with water content, approaches for measuring Matric Potential have received less attention until recently. In this review, a critique of current methods to measure Matric Potential is presented, together with their limitations as well as underexploited opportunities. The relative merits of both direct and indirect methods to measure Matric Potential are discussed. The different approaches needed in wet and dry soil are outlined. In the final part of the paper, the emerging technologies are discussed in so far as our current imagination allows. The review draws upon current developments in the field of civil engineering where the measurement of Matric Potential is also important. The approaches made by civil engineers have been more imaginative than those of plant and soil scientists.
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a porous matrix sensor to measure the Matric Potential of soil water in the field
European Journal of Soil Science, 2007Co-Authors: William R. Whalley, L. J. Clark, W.a. Take, N. R. A. Bird, P. K. Leech, R. E. Cope, Chris W. WattsAbstract:The Matric Potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring Matric Potential) typically only operates in the range 0 to -85 kPa. In this paper, we report the development of a porous-matrix sensor to measure Matric Potential in the approximate range -50 to -300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of Matric Potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of Matric Potential when soil dried to Matric Potentials more negative than -80 kPa. The porous-matrix sensors appeared to give reliable readings of Matric Potential in soil down to -300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable Potential to help understand plant responses to drying soil.
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A porous‐matrix sensor to measure the Matric Potential of soil water in the field
European Journal of Soil Science, 2007Co-Authors: William R. Whalley, L. J. Clark, W.a. Take, N. R. A. Bird, P. K. Leech, R. E. Cope, Chris W. WattsAbstract:The Matric Potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring Matric Potential) typically only operates in the range 0 to -85 kPa. In this paper, we report the development of a porous-matrix sensor to measure Matric Potential in the approximate range -50 to -300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of Matric Potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of Matric Potential when soil dried to Matric Potentials more negative than -80 kPa. The porous-matrix sensors appeared to give reliable readings of Matric Potential in soil down to -300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable Potential to help understand plant responses to drying soil.
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The design of porous material sensors to measure the Matric Potential of water in soil
European Journal of Soil Science, 2001Co-Authors: William R. Whalley, N. R. A. Bird, Chris W. Watts, M. A. Hilhorst, J. Balendonck, D.j. LongstaffAbstract:Summary In recent years the use of porous material sensors for Matric Potential, which were originally intended for soil drier than −100 kPa, has been extended to wet soils. In these wetter soils, unpredictable behaviour of the sensors has been reported. We have studied the design of porous material sensors of Matric Potential in soil and propose a hypothesis to explain this unpredictability, and suggest recommendations for a design of sensor which will behave more reliably. The development of an experimental porous material sensor of Matric Potential based on this design is described. It operates between 0 and −60 kPa, and both the drying and wetting moisture characteristics were measured. In this sensor the porous material was a ceramic and its water content was measured with a dielectric water content sensor. We tested a simple closed-form hysteresis model to convert the measured water content of the porous material into Matric Potential under laboratory conditions. This was shown to give better results than using a calibration based on the drying moisture characteristic curve, where the predicted Matric Potentials were too small. The use of the experimental sensors in the field environment is described. Both types of sensor were installed using the same procedure. As far as we are aware the experimental sensor described in this paper is the first porous material sensor of Matric Potential that can be installed in the same way as a conventional tensiometer. Both conventional tensiometers and the experimental porous material sensors gave similar estimates of Matric Potential.
Chris W. Watts - One of the best experts on this subject based on the ideXlab platform.
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Estimating penetrometer resistance and Matric Potential from the velocities of shear and compression waves
Soil Science Society of America Journal, 2013Co-Authors: Weida Gao, M. Jenkins, Chris W. Watts, Tao Ren, Ho-chul Shin, Shahram Taherzadeh, Keith Attenborough, William R. WhalleyAbstract:Recently there has been interest in using the velocity of elastic waves to deduce soil physical properties. We wanted to validate the suggestion that the small strain shear modulus has a relatively simple linear relationship with penetrometer resistance. We were also interested in testing published equations for predicting shear wave velocity with an independent data set. Three soils were investigated in this study: a loamy sand soil and two silty clay loam soils. The soils were packed into cores with vertical axial stresses of 30, 200, or 1000 kPa. Following saturation, they were drained to a range of Matric Potentials between −10 and −500 kPa. After equilibration, we measured the velocities of shear (S wave) and compression (P wave) waves as well as the penetrometer resistances. Our data confirmed a previous proposal that the penetrometer resistance was an approximately linear function of the small strain shear modulus but tested the relationship by direct measurement. The relationships were found to have some sensitivity to soil type. Nevertheless, we show for the first time that there is considerable Potential for using S wave velocity to deduce penetrometer resistance with a calibration that is relatively insensitive to soil type. Although estimation of the Matric Potential with either shear or compression wave velocity was found not to be very accurate, the possibility for estimating the Matric Potential from an elastic wave velocity given a priori knowledge of the void ratio is an interesting opportunity.
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a porous matrix sensor to measure the Matric Potential of soil water in the field
European Journal of Soil Science, 2007Co-Authors: William R. Whalley, L. J. Clark, W.a. Take, N. R. A. Bird, P. K. Leech, R. E. Cope, Chris W. WattsAbstract:The Matric Potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring Matric Potential) typically only operates in the range 0 to -85 kPa. In this paper, we report the development of a porous-matrix sensor to measure Matric Potential in the approximate range -50 to -300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of Matric Potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of Matric Potential when soil dried to Matric Potentials more negative than -80 kPa. The porous-matrix sensors appeared to give reliable readings of Matric Potential in soil down to -300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable Potential to help understand plant responses to drying soil.
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A porous‐matrix sensor to measure the Matric Potential of soil water in the field
European Journal of Soil Science, 2007Co-Authors: William R. Whalley, L. J. Clark, W.a. Take, N. R. A. Bird, P. K. Leech, R. E. Cope, Chris W. WattsAbstract:The Matric Potential of soil water is probably the most useful assessment of soil water status. However, the water-filled tensiometer (the benchmark instrument for measuring Matric Potential) typically only operates in the range 0 to -85 kPa. In this paper, we report the development of a porous-matrix sensor to measure Matric Potential in the approximate range -50 to -300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of Matric Potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water-filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of Matric Potential when soil dried to Matric Potentials more negative than -80 kPa. The porous-matrix sensors appeared to give reliable readings of Matric Potential in soil down to -300 kPa and also responded appropriately to repeated wetting and drying. This porous-matrix sensor has considerable Potential to help understand plant responses to drying soil.
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The design of porous material sensors to measure the Matric Potential of water in soil
European Journal of Soil Science, 2001Co-Authors: William R. Whalley, N. R. A. Bird, Chris W. Watts, M. A. Hilhorst, J. Balendonck, D.j. LongstaffAbstract:Summary In recent years the use of porous material sensors for Matric Potential, which were originally intended for soil drier than −100 kPa, has been extended to wet soils. In these wetter soils, unpredictable behaviour of the sensors has been reported. We have studied the design of porous material sensors of Matric Potential in soil and propose a hypothesis to explain this unpredictability, and suggest recommendations for a design of sensor which will behave more reliably. The development of an experimental porous material sensor of Matric Potential based on this design is described. It operates between 0 and −60 kPa, and both the drying and wetting moisture characteristics were measured. In this sensor the porous material was a ceramic and its water content was measured with a dielectric water content sensor. We tested a simple closed-form hysteresis model to convert the measured water content of the porous material into Matric Potential under laboratory conditions. This was shown to give better results than using a calibration based on the drying moisture characteristic curve, where the predicted Matric Potentials were too small. The use of the experimental sensors in the field environment is described. Both types of sensor were installed using the same procedure. As far as we are aware the experimental sensor described in this paper is the first porous material sensor of Matric Potential that can be installed in the same way as a conventional tensiometer. Both conventional tensiometers and the experimental porous material sensors gave similar estimates of Matric Potential.
C E Mullins - One of the best experts on this subject based on the ideXlab platform.
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influence of soil temperature and Matric Potential on sugar beet seedling colonization and suppression of pythium damping off by the antagonistic bacteria pseudomonas fluorescens and bacillus subtilis
Phytopathology, 2004Co-Authors: Christoph Schmidt, F. Agostini, Carlo Leifert, K Killham, C E MullinsAbstract:ABSTRACT Pseudomonas fluorescens B5 and Bacillus subtilis MBI 600 colonized sugar beet seedlings at Matric Potentials of -7 x 10(3), -140 x 10(3), and -330 x 10(3) Pa and under five temperature regimes ranging from 7 to 35 degrees C, with diurnal fluctuations of 5 to 22 degrees C. No interaction between Matric Potential and temperature was observed. In situ bioluminescence indicated physiological activity of Pseudomonas fluorescens B5. Colonization of the root at >/=4 cm below the seed decreased at very low Matric Potential (-330 x 10(3) Pa). Total population size of Pseudomonas fluorescens B5 per seedling was significantly increased at -140 x 10(3) Pa. However, Matric Potential had no significant effect on the population density of Pseudomonas fluorescens per gram of root fresh weight and did not affect the distribution of the population down the root. Total population size per seedling and downward colonization by Pseudomonas fluorescens B5 were significantly reduced at high temperatures (25 to 35 degrees C). Maximum colonization down the root occurred at intermediate temperature (15 degrees C) at both Matric Potentials (-7 x 10(3) and -140 x 10(3) Pa). Addition of B. subtilis MBI 600 to the seed had no effect on rhizosphere populations of Pseudomonas fluorescens B5. Populations of B. subtilis MBI 600, which consisted largely of spores, were slightly reduced at lower Matric Potentials and were not affected by temperature. Survival and dry weight of plants in soils infested with Pythium spp. decreased with increasing soil temperature and Matric Potential, indicating an increase in disease pressure. However, there was no significant interaction between the two factors. At -330 x 10(3) Pa, soil dryness but not Pythium infection was the limiting factor for plant emergence. At temperatures of 7 to 25 degrees C and Matric Potentials of -7 x 10(3) to 120 x 10(3) Pa, treatment with Pseudomonas fluorescens B5 increased plant survival and dry weight. At 7 degrees C and -120 x 10(3) Pa, there was almost complete emergence of seeds treated with Pseudomonas fluorescens B5. Antagonistic activity of Pseudomonas fluorescens B5 decreased with increasing soil temperature and decreasing Matric Potential. At 25 to 35 degrees C and -7 x 10(3) Pa, no effect was observed. In regimes with different day and night temperatures, the maximum (day) temperature was decisive for disease development and antagonistic activity. B. subtilis MBI 600 displayed no significant antagonistic effect against Pythium ultimum and did not influence the performance of Pseudomonas fluorescens B5 in combined inocula.
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use and accuracy of the filter paper technique for measurement of soil Matric Potential
European Journal of Soil Science, 1995Co-Authors: R.n. Deka, Morgan Wairiu, P. W. Mtakwa, Elmar M. Veenendaal, C E Mullins, J. TownendAbstract:Summary A filter–paper technique that can be used to measure the Matric Potential of field soil is described in detail. When a calibrated batch of filter papers is used, the precision is limited by the variability between individual papers and the limitation of weighing to the nearest mg. The absolute accuracy is also limited by the instruments used for calibration. There was reasonable agreement between batches of the same type of paper, suggesting that our generalized calibration curves can be used for Whatman No. 42 filter papers where accuracy is not paramount. For Potentials ≥−2.5 MPa, papers need to be equilibrated with the soil for 6 d. To achieve the same accuracy at lower Potentials longer equilibration periods are required. Results suggest that the technique should be effective down to at least −100 MPa if soils are allowed to equilibrate fully with the papers. Coefficients of determination (r2) for the calibration lines were all ≥0.92. A regression of log(-Matric Potential) measured by the filter paper technique against measurements made using tensiometers and a psychrometer over a range of Potentials between −1 kPa and −10 MPa gave an r2 value of 0.995.
Kristine Bolte - One of the best experts on this subject based on the ideXlab platform.
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Determination of critical soil water content and Matric Potential for wind erosion
Journal of Soils and Sediments, 2011Co-Authors: Kristine Bolte, Peter Hartmann, Heiner Fleige, Rainer HornAbstract:Purpose Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θ_crit.) for deflation was extended to include Matric Potential (Ψ_crit.) as well. The focus of this paper is to quantify the Θ_crit. and Ψ_crit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψ_crit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height. Materials and methods The influence of soil water content and Matric Potential upon wind erosion was tested under wind tunnel conditions. Both were investigated in N = 49 wind tunnel experiments for a sandy Podzol topsoil from north-western Germany under a typical, constant free-stream velocity of 6.8 m s^−1. The surface (0–0.2 cm) water content was measured using a microwave sensor; Matric Potential at 0.5 cm depth was measured by laboratory tensiometer and sediment discharge was measured by modified Wilson and Cooke and combined suspended sediment traps and saltiphone. The superficial (0–0.2 cm) Matric Potential cannot be measured directly and was thus modelled using a van Genuchten retention curve model. Results and discussion The range of Θ_crit. was determined to be between 4.9 and 4.0 wt.% at the soil surface; the Ψ_crit. ranged from −75 to −43 kPa at a depth of 0.5 cm. Modelled Matric Potential at the soil surface resulted in lower values between −1.3 and −2.3 MPa as a consequence of steep gradients within soil layers. The reduction of the Θ_crit. and Ψ_crit. led to a steeply significant, almost 20-fold increase in soil losses, projected at 0.56 up to 11.00 Mg ha^−1 h^−1. The ranges of Θ_crit. and Ψ_crit. were ensured by both statistical ascertainment and impulse detection method for validation. The latter yields the specific process-based Θ_crit. and Ψ_crit. at the initiation of erosion and is hence considered the more precise threshold parameter. The impracticability of measuring the soil surface Matric Potential directly requires its modelling or derivation from measurement of relative humidity—which is only applicable for soils in equilibrium with atmospheric humidity. The modelled Matric Potentials are much lower compared to those measured at 0.5 cm depth in consequence of steep gradients within soil layers. Erosion data derived by wind tunnel experiments are not directly comparable to field data, as the wind tunnel device facilitates neither the avalanching process nor the development of a flow saturated with sediment amongst others. Discrepancies of measured sediment discharge compared to those in the literature are most of all attributable to a different reference surface area of erosion in wind tunnel experiments. Conclusions Wind tunnel experiments showed that the initiation of wind erosion can be attributed to certain ranges of Θ_crit. and Ψ_crit.. Specifying the interparticle (capillary) forces Ψ_m provides a precise parameter for describing soil strength. The Ψ_m can be regulated by conservation tillage. Measurements of soil sediment discharge at typical Θ and wind velocity indicate that the sandur plains in north-western Germany are endangered by wind erosion. Besides the regulation of soil moisture and Matric Potential, conservation soil management or the installation of shelter belts and hedges increase the overall surface roughness across various scales and hence reduce the wind erosion risk.
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Determination of critical soil water content and Matric Potential for wind erosion
Journal of Soils and Sediments, 2010Co-Authors: Kristine Bolte, Peter Hartmann, Heiner Fleige, Rainer HornAbstract:Purpose Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θcrit.) for deflation was extended to include Matric Potential (Ψcrit.) as well. The focus of this paper is to quantify the Θcrit. and Ψcrit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψcrit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height.