Ψ in Problem Set 2
I'll just provide clarifications for some of your questions, since answering the questions that require confirmation would basically be the same as answering our own questions from the problem set.
Yes, the most common pore size is the same as the dominant pore size.... the same as it was determined in the lab assignment #3.
Yes, since the soil (mentioned in question #3) is well vented to atmosphere, you can assume Ψa = 0
For question 3b, once you finish all calculations needed for question 3a check what is the direction of water flow in tables I and II. That will help you decide which of those data were obtained before and after the rain. Remember that T (water tension) is only giving us info on the impacts of matric potential on overall potential energy of soil water molecules.
Hi Dr Maja, I have obtained the direction of water flow in the two tables. For the first table, the direction of flow is downwards and in table 2, the direction flow is towards the opposite sides from the midpoint. Does this indicate that table 2 is "before", because the water potential at point B is greater than point A, more organic matter and decomposition on soil surface causes the flow from a higher total potential at point B to lower water potential at point A? Table 1 would be "after" rain, because after the rain,leaching occurs and most of the nutrients and solutes are drained down to the layers below, creating a higher potential at point A than point C and B? please do correct me if i am wrong..
Besides, I have a few more questions in problem set 2.. Q 5c), how do I obtain the volume? I know that the volume of water at saturation is the pore volume because all of the pores are filled with water.. Besides, is the bulk density of the soil sample = mass of oven-dried soil/ total soil volume OR mass of moist soil/ total soil volume..?
Q 6, compaction reduces pore size and less air and water in soil decreases the thermal conductivity of soil. So would it be better to leave it less compacted so that the house can be well insulated?
Similar to Maja's response above, I cannot directly answer your question without giving you the answer. However, I can help clarify the question. In part b) of question #2 you are being asked to compare the two tables, and based on the direction of flow, indicate which table you think is before a rain event, and which table (I or II) is immediately following a rainfall event. In your answer think about the total potential values at different depths, and what the direction of flow suggestions. Beyond that,Re I cannot confirm whether or not your answer above is correct.
In Question 5c) - You are on the right track. If you know the pore volume (units?), how might you figure out how many cm3 this is in this soil sample? For the definition of bulk density, please see you lecture notes.
Question 6 - I am happy to answer a specific question as long as you are not asking me to 1) confirm whether or not your answer is correct or 2) to answer the question asked in the assignment. For this question, think about thermal properties and how they would vary if the soil were compacted. Then based on that you make deduce your answer.