Homework I - University of Florida
Homework I Soils in the Environment Name ______________________________
Answer the following questions using material from lecture and/or your text. Homework is due on Thursday, May 21st , in class.
1. Soil A contains 40% sand, 40% silt and 20% clay.
Soil B contains 60% sand, 10% silt and 30% clay
What is the soil textural class of soil A? _______________
What is the soil textural class of soil B? _______________
Which soil has the greater specific surface area? _______________
2. A 40 g soil sample is placed in a 1-Liter sedimentation cylinder. After shaking the
cylinder to suspend the particles, a hydrometer reading is taken after 1 minute. The
hydrometer reading is 30 g/L.
What material remains in suspension after 1 minute? ___________________
What material has settled? _________________
What is the % sand content of the sample? ________________________
The soil above is allowed to settle for 6 hours. The hydrometer reading at that time is
8 g/L.
What material remains in suspension after 2 hours? ____________
What is the % clay content of the sample? ________________
What is the % silt content of the sample? _________________
What is the soil textural class? _________________________
3. You have a 100 cm3 sample of soil A. The sample is oven dried and weighed. The weight is 160 g.
What is the bulk density of soil A? ___________________
What is the % porosity of soil A? ____________________
4. You have a 100 cm3 sample of soil B. The sample is oven dried and weighed. The weight is 120 g.
What is the bulk density of soil B? ___________________
What is the % porosity of soil B? ____________________
Which soil (A or B) can hold more water when saturated? _____________________
5. You obtain a soil sample with a volume of 400 cm3. It has a moist weight of 450 g and an oven- dry weight of 400 g. Determine the soil bulk density, the porosity, the volumetric water content and the gravimetric water content.
6. Soil water potentials:
100 cm
75 cm
50 cm
25 cm
0 cm reference
Note the soil diagram above. Point A is at 75 cm; point B is at 25 cm. The matric potential energy at point A is -100 cm and the matric potential energy at point B is -200 cm.
What is the total potential energy at point A?
` What is the total potential energy at point B?
Will water flow between the points?
If so, in what direction?
7. Soil Water potential:
400 cm
300 cm
200 cm
100 cm
0 cm reference
Note the soil diagram above. Point A is at 300 cm; point B is at 100 cm. The matric potential energy at point A is -400 cm and the matric potential energy at point B is -100 cm.
What is the total potential energy at point A?
` What is the total potential energy at point B?
Will water flow between the points?
If so, in what direction?
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A
B
A
B
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