Course talk:APBI200

From UBC Wiki
Jump to: navigation, search


Thread titleRepliesLast modified
hydraulic conductivity000:55, 14 February 2020
Printers down Feb 13022:47, 13 February 2020
Wood chip question 2122:35, 13 February 2020
field capacity in Q3, problem set 2104:21, 13 February 2020
wood chips104:17, 13 February 2020
Forestry Orientation Leader Application!001:49, 12 February 2020
Lab assignment curves200:58, 12 February 2020
Lab 3 Assignment- Dominant Pore Size119:08, 11 February 2020
Another practice exam question214:50, 7 February 2020
midterm 1 (1d)414:48, 7 February 2020
Bulk density question504:32, 7 February 2020
Midterm #1002:12, 7 February 2020
broken parent material links202:01, 7 February 2020
Practice exam question101:44, 7 February 2020
isomorphic substitution in kaolinite?101:40, 7 February 2020
4 soil formation processes tested?101:27, 7 February 2020
Practice midterm220:17, 6 February 2020
2 concept questions 219:22, 6 February 2020
Where to find graphing paper219:05, 6 February 2020
Best answers are now posted in hallway 001:34, 6 February 2020
First page
First page
Previous page
Previous page
Last page
Last page

hydraulic conductivity

In Question 5 of the problem set, I am having a hard time understanding if hydraulic conductivity flows quicker (and is thus higher) when matric potential is lower (-0.5) versus higher (-0.01). The definition of Darcy's law says that the rate at which water flows is directly proportional to the water potential gradient, but this would make me think that, the lower the matric potential (more negative), the faster the water will flow. This doesn't make sense when I think about it, though, because, the lower the matric potential, the more it is directly countering the gravitational potential. Could you clarify this for me?

00:55, 14 February 2020

Printers down Feb 13

Hi everyone I understand that pay-for-print on-campus is down today (again). No late penalty if you are in Thursday lab and you hand in lab 4 tomorrow (by noon) Sandra

22:36, 13 February 2020

Wood chip question 2

Hi Sandra, I saw the previous question posted about the wood chip, I am also confused. I agree that wood chips(organic) has high porosity and low Cv, but according to UBC wiki "soils with high Cv are buffered against temperature change." It seems like organic wood chips will not help avoid the rapid fluctuations in soil temperature (which I don't think is true.)

20:26, 13 February 2020

Becca, consider thermal diffusivity in relation to subsurface temperature changes; thermal admittance relates to surface temperature changes.

1st be clear that in this question there is an organic layer (wood chips) overlying the mineral soil. The question (#4) asks how the organic layer on top of the mineral soil will impact the temperature of the mineral soil (in winter). Consider whether or not, the "heat" lost from the mineral soil in winter will be less, the same or greater with an organic mulch on top; and why?

22:31, 13 February 2020

field capacity in Q3, problem set 2

We've defined field capacity as the water content of soil after rapid drainage. We've also defined field capacity as being a soil's water content when its matrix potential is somewhere between -10 and -30 kPa.

In question 3 of the problem set, these definitions seem to conflict with the red soil. How do I square this?

22:10, 12 February 2020

Spencer, Consider that the concept of field capacity is qualitative (i.e. descriptive) thus the qualitative definition of the water content of soil after the "rapid" drainage (or water drained by gravity). Quantitatively we define this value as the soil water content at -10 to -33 KPa (depending on soil texture). Thus we measure field capacity of the "red" soil in question #3 (problem set #2) at -33 KPa.

04:21, 13 February 2020

wood chips

In class, I think we were given some contradicting information. In the section about Heat Storage Capacity, Dr. Brown said organic matter has a low Cv, but later in the lecture she said woodchips would have a high Cv. Which one is it?

21:51, 12 February 2020

As per lecture slides (lecture #15 soil thermal properties), slide 19 - water has a high Cv, air has low Cv Thus an organic mulch such as wood chips, which as high porosity (i.e. lots of air) would have a low Cv

Apologies if there was any confusion during class discussion.

04:17, 13 February 2020

Forestry Orientation Leader Application!

The Faculty of Forestry is looking for Orientation Leaders for Imagine Day 2020! I wanted to share this opportunity with you all as it is a really fun volunteer position that provides you with the opportunity to practice your leadership and communication skills while helping build a sense of community among our new incoming student body!

I've attached the link to applications below.

Please let me know if you have any questions!


01:49, 12 February 2020

Lab assignment curves

Hello! Can we make the curves using a software like excel and then print the graphs or do we need to draw them by hand?

00:40, 11 February 2020

Yes, of course ....

18:00, 11 February 2020

Another nice trick is to make your graph in xls, copy it to powerpoint, and annotate in powerpoint

00:58, 12 February 2020

Lab 3 Assignment- Dominant Pore Size

Hi there,

I am a little confused about how to determine/calculate dominant pore size. Is the dominant pore size the same as the radius (mm) of pores corresponding to AIV? Also, how would this calculation relate to the largest and smallest pore sizes?

18:32, 11 February 2020

Hint - pls check the lab manual, specifically an info box shown on the page no.38, where explanations of AEV and AIV are provided

19:08, 11 February 2020

Another practice exam question

For the calculation question, #1b, if I have the mass of the water (365 g), along with the bulk density (1.196 g/cm^3) and the volume of the moist soil sample (740 cm^3), how do I calculate the volume of the water? Thank you.

06:58, 7 February 2020

Try to use the formula mass=ρv, the density for water is ρ=1g/cm^3. The answer should be 365cm^3.

07:27, 7 February 2020

Thank you. Upon further reflection, this is what I got, too. Yay!

14:50, 7 February 2020

midterm 1 (1d)

When a soil is saturated would the water content be 100% because the pores will be filled water or rather 50% air and 50% water?

04:21, 7 February 2020

For this question (part b) you determine the Mw (the mass of water) and calculate the volume of water (Vw). Consider the definition of volumetric water content θ = Vw/Vt

04:49, 7 February 2020

How do you determine the water content at saturation (part d)?

07:31, 7 February 2020

Hi Amy,

When a soil is saturated, water occupies all of the pore space in that soil - this means that the volume of water equals the volume of the pores!


07:56, 7 February 2020

Hi! I solved for porosity (using a particle density of 2.65 g/cm^3) and got f=.54 or 54%. Does this seem reasonable?

14:48, 7 February 2020

Bulk density question

Hello! When calculating bulk density, you only consider sand, silt,and clay; nothing above 2 mm, correct? Thank you.

08:20, 6 February 2020

No, not correct.
Please see the response to a very similar question under post titled "2 concept questions"

16:46, 6 February 2020

Hi Maja,

Thanks. My understanding now is that for bulk density, when you use the core method, you include coarse fragments, whereas when you use the excavation method, you don't, either for mass or volume. Does this seem reasonable?

22:31, 6 February 2020

No. The core method would generally be used in cases where you have limited to no coarse fragments. The excavation method is used when you have significant coarse fragments. Please see the section in Brady on soil density if you are unsure of the concept.

Amy, as you are a graduate student, you may wish to consult a standard reference manual (e.g. Carter) HOWEVER this level of detail is well beyond this introductory soil science course.

01:25, 7 February 2020

Hi Sandra,

Thanks. From your response on the '2 concepts' thread, it sounds, for the excavation method, like coarse fragments are sieved out and disincluded for both Ms and Vt values. For the core method, Maja said that coarse fragments would be included in both Ms and Vt. Do you agree?

04:32, 7 February 2020

Midterm #1

Midterm #1, Friday Feb 7th

This midterm will cover materials from:

  • All lectures prior to the exam (including soil water 4)
  • Material from the lab manual on soil parent materials, texture and soil water (Labs 2, 3 and 4)
  • Lab assignments for labs 2 and 3
  • Problem set #1
  • Practice exam questions

The exam format will include:

  • multiple choice, multiple answer and fill in the blank questions
  • compare and contrast questions (similar to those you have done in lab assignments and problem set #1)
  • calculations no calculation sheet, but you should bring a calculator
  • short answer / interpretation questions (similar to questions from the practice exam on Feb 5)

The quizzes in Soilweb200 are a useful starting point

11:55, 28 January 2020

broken parent material links

Just FYI, the links to the Resulting Parent Materials in the table on this page ( are broken.

01:38, 7 February 2020

Spencer, thank you for letting us know. As it will take 1-2 days to fix this link... You can find the parent material information at

Alternatively your lab manual provides a good overview.

02:00, 7 February 2020

Thank you for letting me know. I asked our IT folks to fix those broken links.
In the meantime, pls use the main URL for that parent material website -

02:01, 7 February 2020

Practice exam question

I remember that mineral matter is a better conductor comparing with organic matter. However, SOM has large number of negative charges and high water retention. Why isn't this the other way around?

00:12, 7 February 2020

Becca, we will cover thermal properties of soils after the midterm exam. IF you are referring to hydraulic conductivity consider that hydraulic conductivity is maximum in saturated conditions, and that when a soil is saturated, large well connected pores are better conductors of water than small pores. See lecture #11

01:44, 7 February 2020

isomorphic substitution in kaolinite?

as the layers in kaolinites are held much tighter (through hydrogen bonding) than the layers of montmorillonites which are held together by coulombic forces, are there no isomorphic substitutions in kaolinites as water molecules cannot enter the interlayer space? or are there still isomorphic substitutions but just more limited compared to montmorillonites

22:41, 6 February 2020

You are correct about the structure of these two secondary phyllosilicate clay minerals. Kaolinite being a 1:1 phyllosilicate, where the layers are tightly held together by H bonding. Montmorillonite, a 2:1 phyllosilicate clay mineral, with shrink-swell properties.

Isomorphic substitution is a separate concept; the process by which one element of similar size fills the position of another within the crystal structure of a mineral. Commonly Fe2+ or Mg2+ replacing Al3+ in the octahedral layer of Al3+ replacing Si4+ in the tetrahedral layer. This substitution results in a net negative charge. Montmorillonite has a high degree of isomorphic substitution, while Kaolinite has very low isomorphic substitution.

01:40, 7 February 2020

4 soil formation processes tested?

I was wondering if the 4 soil formation processes will be tested? It wasn't covered during lecture but its in the soilweb200. Below are the 4 processes

1) Additions - the addition of organic material (i.e., addition of dead root mass in grassland ecosystems). 2) Transfers - the downward movement of soluble material in water (i.e., redistribution of calcium carbonate in a soil profile). Note that while the distribution of material with depth has changed, the material has not been completely lost from the soil. 3) Transformations - the weathering of primary minerals to secondary minerals, or the decomposition of organic matter. 4) Removals - the complete loss of material from the soil profile (i.e., the loss of calcium carbonate in a soil forming in a humid environment).

20:43, 6 February 2020

Celeste, these concepts will be included later in the course. For now, focus on the 5 factors of soil formation presented in lecture #3

01:27, 7 February 2020

Practice midterm

I was having hard time looking for the answer if the 2 practice midterms -- are they provided?

06:20, 5 February 2020

Two examples of past midterm exams are posted at
Format of your midterm exams will be exactly the same as those examples

17:04, 5 February 2020

Note: we do not post answers to practice exam, lab assignments or problem sets. IF you have any specific questions you can get help during office hours or ask in this forum. IF you are asking about a specific questions, please indicate the assignment your are referring to and the question.

19:36, 6 February 2020

2 concept questions

I am a little confused about 2 concepts. 1.) Is soil colloids secondary minerals? 2.) When calculating bulk density Ms/Vt, should we use the total volume which include the coarse fragment?

02:17, 6 February 2020

-Term 'soil colloid' refers to a size of particles that are smaller than 0.002mm; and those particles can be very different in terms of their nature. As mentioned in the lecture on Jan 15, soil colloids include pyllosilicate minerals, Fe & Al oxides/hydroxides, amorphous minerals, and organic matter.
Pyllosilicate minerals, Fe & Al oxides/hydroxides, and amorphous minerals are all secondary minerals.

-Total volume of a soil is comprised of both coarse fragments (ie those with diameter larger than 2mm) and fine particles (ie those with diameter smaller than 2mm).

03:02, 6 February 2020

Calculating bulk density core vs excavation method

In agricultural soils, bulk density can commonly be determined using the core method. However in rocky forest soils (i.e. coarse fragments > 25%), the excavation method is often used. The excavation method involves digging out a small hole, then oven drying (at 105°C) and weighing the excavated soil. The volume of the excavation is determined by lining the hole with plastic film and filling it completely with a measured volume of water (or sand, or silicon beads). Coarse fragments (diameter > 2 mm) are sieved out and bulk density is calculated as the mass of dry, coarse fragment-free soil per volume of the excavated soil, where volume is also calculated on a coarse fragment-free basis. Full details on this method are online at

19:21, 6 February 2020

Where to find graphing paper

Hi, I'm just wondering where can I get or download the graphing paper? Cuz I didn't receive it during the lab last Friday and many of my friends from that day's lab don't have it as well.


02:17, 6 February 2020

If by 'graphing paper' you mean the semi log paper needed for lab #3 assignment, it can be found at this wiki page .... it is posted there as a PDF

02:51, 6 February 2020

IF you are looking for "regular" graph paper for lab #4, you can get it in the lab McMl 102A during office hours (today 12:00-1:00 pm)

19:05, 6 February 2020

Best answers are now posted in hallway

Hi everyone,
Answers to 6 questions from today's practice exam session are now posted on the wall across Maja's & Sandra's offices in MCML building.
These answers will NOT be posted in wiki.
Questions are posted in wiki at "lecture Notes" page for Feb 5th

21:04, 5 February 2020
First page
First page
Previous page
Previous page
Last page
Last page