Lab Assignment #7
Please post questions about Lab Assignment 7 here.
Hey! I was wondering what could be some reasons I found the soil profile at the field pit location to have finer soil texture. I thought soil texture was really hard to change so was I wrong when I felt a finer texture? Thanks!
Our campus soils have quite coarse texture with very little clay in them. It is possible that organic matter (that accumulated in the A horizon of the cultivated soil pit) confused you to think that the texture is fine in that horizon. Organic matter tends to give that soapy fleeing, similar to silt.
Hey Maja, I am sorry that I forgot the relationship between soil pH and soil formation. My assumption is: Soil that has low pH can have relatively stable aggregates because the concentration of base cations (e.g. Na+) in acidic soil is really low, so the DDL is relatively thin, so the aggregates are more stable. Is that correct?
By the way, the reason why forest soil has low pH is that plant residues are decomposed by soil organisms, and that decomposition can cause the release of some materials which can form acid. Does it sound right? Because both forest pit and agricultural pit are in UBC farm, so the difference of precipitation is negligible. Based on that statement, what is the main factor that cause the difference of soil pH between forest soil and agricultural land soil?
Thank you very much!
In your 1st question, I am not sure what do you refer to by "soil formation". The process of aggregate stability that you described is correct, but aggregate stability is not a soil formation...
Soils formed under coniferous forests are acidic because their debris is acidic and when decomposed various organic acids are released. These acids then enhance mineral weathering (which results in release of Fe & Al ions, which in turn further acidify soils).
Soils at UBC campus under their natural setting tend to be acidic. Soils at the UBC Farm have been in the agricultural production for 50 yrs and since their natural acidity is not suitable for majority of agricultural crops liming is commonly done to raise their pH.