Most ecohydrology studies quantify matrix and positive pressure potential when assessing the benefits of trees in reducing the risk of flooding. Comparisons are usually made between forested and non forested sites using pressure transducer tensiometers. I would like to know how soil potential is related to water flow in the soil. The significance of water potential in establishing soil moisture retention is clear, but that of pore pressure,water flow and pore size is still hard for me to understand
Matrix potential is combination of the forces of attraction of water to the soil matrix and between the water itself. As the pore size of the soil reduces, there is a significant increase in the specific surface area of soil matrix which increases the adhesion forces between the water and matrix. The water potential which is the energy needed to remove this water ( overcome these forces of attraction) will increase. Smaller pore size will lead to slow movement ( downward drainage), but will also increase the capillary rise in soils. As F.Lehman ( Darcy's equation and Richards equation) has also put it, smaller pores will slow the hydraulic conductivity of the soil. Low tensiometers values indicate the easy of soil to release its water which correlates to bigger pores spaces, and also not very dry conditions and Vice-versa.
Thank you, it's now clearer than before. Anthony when you say low tensiometer values, I presume you mean less negative values of matrix potential which are a characteristic of wet soils?
Sorry Marapara, I have considered negative sign and was looking at just magnitude A fully saturated soil should have a zero potential.. very dry should Less negative ( with bigger magnitude ) and flooded soils should have a potential which is positive. Most of what we encounter with tensiometer is unsaturated soils. So its the otherway round.
Take a look to Hillel's book which gives the simplest descriptions about what you are asking for. You have to understand the meaning of water retention curve and how it is connected with pore size distribution, and how these pores affect water movement when they are filled with water. For models look for van Genuchten (1980), for saturated hydraulic conductivity take a look to the paper ird1751, for unsaturated hydraulic conductivity search for Mualem-van Genuchten model
dear sir, water potential and pore size distribution has indirect relationship. means that the larger soil particles has the lower water potential than finer particles with the same amount of water applied on both soil textural class. Generally positive potential energy indicates the water which can flow freely (gravitational water) and higher -ve potential indicates that water is attracted by soil solids.
Lo importante es entender que los poros grandes tienen menor potencial que los poros pequeños.
Dear Marappa,
You need to go through a typical text book of soil physics (Hillel for example), and try to gather the concepts of water flow under positive and negative potentials. But most importantly, you may find many published paper describing these while applying to solving specific problems. Pl. read those, and synthesize to apply to your own area of research interest. Good luck.
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