mid term

1. Why would physical and chemical processes such as wetting/drying and freezing/thawing contribute to aggregate formation?

2. Would field capacity be lower in a sandy soil than in a clay soil?

3. Midterm 2008 question 5: Can we assume the density of the organic matter is 1.3g/cm^3?

1. Wetting/drying and freezing/thawing are physical (not chemical) processes that enhance aggregate formation. They do so, since they (namely thawing and wetting) bring individual particles closer together, allowing them to bond better (which leads to flocculation as the 1st per-requisite for aggregate formation).

2. Clay soil with its higher porosity (than sandy soil), will have the higher field capacity.

3. There was a typo in question #5 in 2008 midterm, hence I replaced it with another example

I don't really understand question 2 on the 2006 midterm. When you ask "what is the charge change resulting from the incorporation of the Mg2+ instead of the Al3+" are looking for something about how it becomes acidic?? Does in become negative? Thanks a lot!

this is related to the isomorphic substitution. And in this example the substitution leads to formation of a negative charge. This is the same example as I used in the lecture.