HW#4_

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University of Akron *

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Mechanical Engineering

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Apr 3, 2024

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Homework#4: Exercise 1: Using the USDA triangle, find the textural class name of soil with 20 % clay, 20 % sand, and 60 % silt? (5 points) -Silt loam Exercise 2 : What are the gravimetric water contents just before and just after irrigation? -Before Irrigation = (1.79 – 1.49)/ 1.49 = 20.13% -After Irrigation = (1.94 – 1.52)/ 1.52 = 27.63 % The bulk density of the soil is 1.3 g/cm 3 . Find the volumetric water contents (5 points) and porosity of the two samples (5 points). Volumetric water contents: Before irrigation = 1.3 x 20.13 = 26.17% After irrigation = 1.3 x 27.63 = 35.92% Porosity for both samples = (2.65 – 1.3)/2.65 = 50.94% Exercise 3: Determine the 2 constant parameters (a and K) of kostiakov equation a = 0.54 K = 4.63 Calculate and draw the cumulative infiltration rate at each time step (time in minutes on Xaxis and cumulative infiltration rate (mm) on the Y axis) - Plotted in excel attached Calculate and draw the instantaneous infiltration rate (time in minutes on X-axis and instantaneous infiltration rate (mm/h) on the Y axis) - Plotted in excel attached
Estimate graphically (from previous question), the saturated hydraulic conductivity (Ks) in (mm/h) ( - Ks = 24.1 mm/h Exercise 4: Calculate actual yield (Y a ) for cotton if average salinity during the growing season is 10.4 dS/m and the minimum (EC min ) and maximum (EC max ) salinity tolerance thresholds are 7.7 dS/m and 25 dS/m respectively. Crop yield under optimal conditions (Y max ) is 1,285Kg/ha Relative yield Slope = (0 -100)/(25 – 7.7) = -5.78% RY = 100 – 5.78*(10.4 – 7.7) RY = 84.394% Actual yield = 84.394 x 1,285/100 = 1,084.46 Kg/ha Calculate the total amount of irrigation water (mm) to be applied to avoid yield losses. Assume EC of irrigation water is 2dS/m and the total consumptive use (ET) of the cotton is 800mm. (10 points) Leaching Requirement (LR) = ECw/ (5ECmin – ECw) LR = 2/ (5*7.7 – 2) = 5.48% ET/(1 – LR) = 800/(1 – 0.0548) = 846.38 mm Extra water needed = 846.38 – 800 = 46.38 mm Exercise 5 In this exercise you will assume that all your capacitance sensors are calibrated and the only difference is related to installation errors. Out of the three volumetric sensors installed, select one (Justify your selection) and compare the obtained volumetric water content with soil water potential (Use excel to draw your graph) (10 points) - The Port 3 sensor was omitted first because it is significantly different from Port 4 and Port 2.
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