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Group assignments 1. (a) Describe how gravimetric and volumetric content are related and in turn, how they are related to matric potential [9marks] (b) What are the forces associated with the potential of water in the soil and when is each important? [6marks] (c ) Write short notes on: i) the soil moisture characteristic curve [5marks] ii) The capillary fringe [5marks] 2. (a) A substantial area of land in Zimbabwe is low land (dambo). Discuss the advantages and disadvantages associated with bottom land farming in these regions [15marks] (b) How could problems associated with bottom land farming be ameliorated? [10 marks] Individual Assignment Assignment I 1) Define soil water potential 2) Water in soils can be expressed: i) Quantitatively ii) Energy status [3marks] Explain clearly how each is achieved. Of the two methods which one has an advantage over the other? [10marks] 3) Discuss the potential or combination of potentials that are responsible for water movement under the following conditions: a) Soil to plant roots [3marks] b) In biological materials [3 marks] c) Under unsaturated soil conditions [3 marks] d) Under saturated soil conditions [3 marks] 4) Write short notes on each of the following terms : a) Osmotic potential b) Gravitational head c) Darcy’s law d) Hysteresis e) Hygroscopic coefficient f) Void ratio g) Air filled porosity [25marks] 5) a) Prove that ᴪ = 0.15/r [5marks] b) Calculate the radius of the largest water filled pores at field capacity and wilting point. [6marks] c) How many centimeters equivalent depth of water are contained in a soil profile 1metre deep if the mass wetness of the upper 40cm is 15% and that of the lower 60cm is 25%. The bulk density is 1.2g/cm3 in the upper layer and 1.4g/cm3 in the deeper layer. [10marks] d) How much water does this soil contain in m3/ha of land. [6marks] 6. From calibration of a neutron probe we know that when a soil’s volumetric wetness is 15% we gwt a reading of 24000cpm (counts per minute) and at a wetness of 40% we get 44000cpm. i) Find the equation of the straight line defining the calibration curve in the form Y = aX + b, where Y is cpm, X is volume wetness, a’ is slope and b is the intercept on the Y-axis. [8marks] ii) Using this equation find the wetness value corresponding to a count rate of 30 000cpm. [2marks] Iii) Prove the following relationship between porosity, particle density and bulk density. 𝜚𝑏 F = 𝜚𝑠 [5marks]