Influence Of Matric Potential Research Articles

Impact of potassium concentration and matric potential on soil stability derived from rheological parameters

The soil solution influences the soil stability in different ways: via water content as due to drainage menisci contract particles, and via the chemical composition including different ions in different amounts. While the first aspect was at least examined on the mesoscale, the second aspect remains widely unexplored when it comes to the influence of single ions on the microscale of soils. Previously published papers indicate a higher soil stability under the influence of potassium that cannot be explained only by its positive effect on plant growth and the enhanced shrinkage and swelling processes caused thereby. Parameters derived from rheological measurements can be used to examine the influence of soil solution in different compositions and matric potentials on soil microstructure. The rheological parameters were obtained by means of an amplitude sweep test where soil samples are subjected to oscillating forces with increasing deflection. From the sample's resistance towards this deformation storage modulus G′ and loss modulus G″ are derived, representing elastic and plastic deformation, respectively. Characteristic stability values of the moduli curves are the end of the linear viscoelastic (LVE) range indicating irreversible deformation and the yield point indicating flow. Additionally, the maximum shear stress during the test was used to characterize the maximum resistance of the sample against deformation. In our investigations we found higher soil stability on the microscale with higher ion concentration and more negative matric potentials. With potassium chloride the LVE range extended and the yield point shifted to higher deformation and stress values. Consequently, the influence of potassium chloride resulted in a higher stability of the microstructure based on the storage and loss modulus as well as the shear stress. With increasing ion concentrations in the soil solution a further increase in microstructural strength was detected. Regarding the influence of matric potential both the shear stress at the end of the LVE range and the maximum shear stress increased with more negative matric potentials, because a higher drainage intensity resulted in higher effective stresses caused by stabilising menisci, cemented bonds due to precipitation of salts and increased number of contact areas between particles. Additionally, the yield point attained higher values for storage and loss modulus, respectively.

Influence of matric potential and soil compaction on growth of the take-all fungus through soil

Growth responses of the take-all fungus, Gaeumannomyces graminis var. tritici , to matric potentials between zero and −0.01 MPa were investigated. Growth was influenced by soil compaction. The range of matric potentials over which the fungus grew well was restricted with increasing bulk density. In soil near saturation, when total gas-filled pore space (GFP) was less than 0.08 cm 3 air cm −3 soil, no growth occurred at any level of compaction, probably because oxygen became limiting. Above GFP 0.27 cm 3 air cm −3 soil, differences in growth due to compaction could not be distinguished. It is argued that, when total GFP was in the range 0.08–0.27 cm 3 air cm −3 soil, the size distribution and number of GFPs are primarily responsible for the differences in growth observed at different levels of compaction. These observations have implications for predicting the impact of changing tillage practice on disease severity.

Influence of matric potentials on carpogenic germination of sclerotia ofSclerotinia sclerotiorum. II. A comparison of results obtained with different techniques

Four techniques to study the influence of soil matric potential on carpogenic germination of sclerotia of Sclerotinia sclerotiorum were compared. These were the inclined box, polyethylene glycol, sealed jars, and tension plates. The inclined box technique showed that at high matric potential (-0.1 to -0.4 bar) percent germination was higher on the soil surface than at 1 cm depth, but the opposite occurred at potentials of less than-1 bar. All techniques showed that at matric potentials close to 0 bar, germination would occur only if sclerotia were on the soil surface and adequate oxygen was available; buried sclerotia failed to germinate and many rotted. The lowest matric potentials that appeared to induce carpogenic germination using the inclined box, polyethylene glycol, and sealed jar techniques were -4, -7, and - 15 bars respectively, With the latter two techniques the matric potentials are probably understated; thus, although sclerotia can germinate in soil well below field capacity, the lower limit is probably that shown by the inclined box technique. This technique provides the closest approximation to field conditions.

The Influence of Matric Potential, Soil Texture, and Soil Amendment on Root Disease Caused by Phytophthora cinnamomi

The Influence of Matric Potential, Soil Texture, and Soil Amendment on Root Disease Caused by Phytophthora cinnamomi

Influence of Soil Water Matric Potential and Hydraulic Conductivity on the Germination of Rape (Brassica napusL.)

The influence of matric potential and hydraulic conductivity on the water absorption and germination of rape (Brassica napus L.) was investigated by comparative studies in three seed-soil water systems. In all systems the rate of germination and total germination were substantially retarded with decreasing matric potential. Hydraulic conductivity of the soil system was demonstrated to be a limiting factor in the germination process. The effects of matric potential and hydraulic conductivity on water absorption followed closely those demonstrated for germination. The influence of matric potential was shown to be comparable to that of osmotic potential provided consideration was given to the hydraulic properties of the soil-seed system.

The Influence of Soil Water Matric Potential on the Strength Properties of Unsaturated Soil

AbstractA study was made of the contribution that matric potential makes to effective stress and therefore the strength properties of two unsaturated soils. From an evaluation of the effective stress parameters C' and ø', and the unconfined strength, the shear strength, effective stress, and the χ factor were estimated as a function of soil water matric potential over the range −0.59 to −15.1 bars.The strength properties of a Gretna clay increased rapidly with decreasing matric potential. In a Wellwood loam, however, the strength properties remained relatively constant over the range −0.59 to −15.1 bars.The influence of matric potential on the strength properties of an unsaturated soil can be described in terms of the contribution that matric potential makes to the effective stress operating in the soil system. A measure of the proportion of the matric potential operative in the effective stress is given by the χ factor which is related to the degree of saturation. Therefore, the influence that matric potential has on the strength of an unsaturated soil is related to the moisture retention properties of the soil.The implications arising from the contribution that matric potential makes to the strength properties of an unsaturated soil are briefly discussed in terms of soil‐plant relations.

Comparison of the effects of soil matric potential and isotropic effective stress on the germination of Lactuca sativa

The matric potential contributes positively to the isotropic effective stress operating in the solid framework of a soil system. Collis-George and Hector (1966) suggested that the matric potential may influence seed germination through its contribution to the effective stress in the solid framework surrounding the seed. Experiments are described which separate the effects of matric potential on seed germination into those that can be attributed to the free energy of the soil water and those that can be attributed to the effective stress in the soil system. The results clearly indicate that (1) seed germination is influenced by the isotropic effective stress in the solid framework of the soil system, and (2) the influence of matric potential on seed germination in the range 0 to - 400cm of water can be wholly attributed to the isotropic effective stress in the solid framework and not to the free energy of the soil water as defined by the matric potential. These conclusions are discussed in terms of the behaviour of other organisms in response to an applied matric potential.