General Course Questions

Here you can post any general questions you have about the APBI 200 course.

Could you please explain what submergence potential is?

And is it the same thing as the hydrostatic potential that us mentioned in the textbook?

Submergence potential is a component of the total water potential and it is operational only in saturated soils. Submergence potential is formed in the same way as matric potential (operational in unsaturated soils) due to attraction between charged soil particles and polar water molecules and capilarity.

More on this topic can be found in your textbook in chapter 5

Hi, Maya. R the role in soil of mites and nematode just grazing on soil bacteria, and stimulate the nitrogen cycle? And does heterotrophic bacteria have any roles other than decompose organic matter? Thank you!

Nematodes (but not mites) feed on bacteria and due to their low N requirement nematodes release surplus of N into soil solution, which then becomes available to other organisms (including plants)

Mites perform other functions such as shredding & mixing of soil material, the also do a bit of burrowing. The can also enhance aggregate formation by ingesting mineral & organic soil particles.

Heterotrophic bacteria decompose organic matter and by doing that they help with the release of the available forms of N, S and P.

All soil organisms also add to the pool of soil organic matter once they die

Hi Maja, should we memorize the multiple steps of mineralization, I mean the chemical reactions of aminization, ammonification and nitrification?

you don't need to memorize the chemical reactions, but you should be able to describe them correctly

Question: I have a question about montmorillonite and kaolinite. Based on my notes, Kaolinite is more stable than montmorillonite. I feel confused about that concept. Could you please briefly explain it? Are they both phyllosilicates?

Answer: Yes, both montmorillonite & kaolinite are members of the phyllosilicate group. However, they have a very different crystalline structure, which also translated into different stability and susceptibility to isomorphic substitution. With 2:1 type of structure, montomorillonite is characterized with weaker bonds within its crystallyne structure and is more prone to isomorphic substitutions and consequently larged number of charges than kaolinite (wiht its 1:1 type of structure)

More on these 2 minerals can be found at http://soilweb200.landfood.ubc.ca/soil-components/1-mineral-components/#Types_of_Soil_Colloids as well as in your textbook (see p.240-244)

Hi Maja:

Im wondering how does a high pH in soil help enhacing the decomposition?

I wouldn't say that pH is ENHANCING decomposition of organic matter, but that pH AFFECTS decomposition of organic matter.

The effect of soil pH on decomposition of organic matter is indirect, since decomposes (i.e heterotrophic soil organisms) all have an optimum pH range in which they are most active.

Hi Maja,

I'm confused with what soil properties enhance nitrate leaching losses

This was one of the questions that was part of the discussion session no.2, so I'll only briefly answer it here.

Nitrate is an anion, hence as such it will mainly be in the soil solution (since as an anion it will be repelled by the negatively charged soil particles). So, think about what conditions lead to easy movement of soil solution....... keeping in mind that soil solution moves through the pore system....

Also to consider are sources of nitrates in soils (i.e., from where are nitrates released and how are they added to the soil).

Hi Maja, I was wondering what is the reason for soil algae and nematodes being smaller than the other kinds of nematodes and algea? Thank you

Soil species of algae & nematodes don't have as much space to grow as their aquatic relatives. Hence, soil species end up being smaller.

Maja, the sizes of the algae cells and the bacteria cells are almost the same. Why the room in soil is limited to algae? Is that because algae cells like to clump together?

Algae are a very diverse group of organisms and they include unicelluar organisms (which would be of the similar size as bacteria) to mulitcellular organisms (such as giant kelp that can grow to up to 50 m in length).

Hi Maja,

Will a soil with no B horizon always be classified as Regosol? For example soil with Ap=10cm, Cg1=20cm, Cg2=30cm is not Chernozemic for sure, but could it be Gleyesol?

Thank you

Hi Diana, according to Maja, "You have to be careful re. making decisions about a soil being a Chernozem, since many soil types will have an Ah horizon. But not every Ah is the Chernozemic Ah (diagnostic horizon. The Chernozemic Ah horizon, need to have several specific properties (e.g., C/<17/1, base satauration >80%, Ca2+ as the dominant ion on the exchange complex)"

Hi Depeng,

Thank you for your reply. The reason I am confused is that the lab. manual says that Regosol is a soil that could not be classified as anything else, but from several Maja's replies to soil order questions it seems that Regosol is primarily a soil with no B horizon. However, say for Gleyesol, we need to have B or C horizon gleyed; but it does not stress that we must have a B horizon of any kind. If so, then can the soil I mentioned above (with Ah and Cg horizons only) be Gleyesol?