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Soil Physics Homework 4 October 19 2009 Due October 26 Water Potential and Retention 1 Assume that a soil has a water table at 0 32 m below the surface Calculate the vertical distributions of the pressure gravitational and total potential J kg in the interval 0 0 5 m assuming that the reference level is at the surface Present the results in a table using steps of 0 1 m see Table below Repeat the calculation for the reference level placed at the water table In each case convert the values of potential to units of energy volume and energy weight z m g p h 0 0 1 0 2 0 3 0 4 0 5 2 A curious student has constructed a manometer tensiometer that uses alloy X instead of mercury Alloy X is insoluble in water is colored liquid at room temperature and has a density of 8 0 Mg m 3 A tensiometer is buried 0 5 m deep in the soil where the pressure potential of the soil water is 1 5 m The surface of the reservoir of alloy X is 0 1 m above the surface How high above the soil surface will alloy X rise in the manometer tube when equilibrium is reached in the system 3 A core sample of 100 cm3 is on a tension table hanging column apparatus At negative pressure potentials hi cm the equilibrium outflow Vi cm3 is read on the burette hi Vi 0 31 10 31 20 30 40 50 60 80 100 120 30 3 29 2 27 5 25 5 23 3 21 5 19 1 17 8 Compute the soil water contents i and plot the soil water retention curve when the bulk density of the soil is 1 38 Mg m 3 Soil Physics Homework 4 October 19 2009 Due October 26 4 Make a graph showing the relative vapor pressure or relative humidity RH at equilibrium with the matric potentials showed in the table below What is the RH range that can be found in field soils with water contents between saturation and wilting point hm kPa 1 10 30 70 100 300 500 1 000 1 500 3 000 7 000 10 000 100 000 5 Columns of Soil A and Soil B are sampled from the field The columns are 1 m long In the laboratory the columns are placed in the upright position with the bottom in contact with the

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