Practice exam #3 - QUESTION 6

Practice exam #3 - QUESTION 6

All questions are posted at the "Lecture notes" page here in wiki. Please post here your discussion, answers, and/or requests for clarification re. the QUESTION #6

MajaKrzic (talk)16:53, 3 April 2020

a) Since there is Ah>10cm, bs > 80% where Ca is the dominant cation, has a massive texture lower in the soil, and maybe its a grassland, I said it belonged to Chernozemic soil order. It also has a Bg layer, so i guess it could also be a Gleyzolic but it doesnt state that the water table fluctuates, so I think Chernozemic is the best fit.

BennettWardman (talk)18:44, 3 April 2020

Bennett, consider what is dominant gleying or the Chernozemic Ah?

SandraBrown (talk)02:44, 4 April 2020

I'm confused why we can conclusively say that this soil is of the Gleysolic order - it has a Chernozemic A horizon and is in a grassland, and also fits the properties of a Gleysol. Is it possible for it to be both? Why does one take precedence over the other?


DeclanTaylor (talk)21:46, 26 April 2020

A) The Goose soil belongs to the Gleysolic order. Its diagnostic horizon is the Bg (also the ABg and BCg horizons) which indicate a fluctuating water table and fluctuating oxidation/reduction conditions.

B) the granular and subgranular structure in the Ah and ABg horizons would allow room for root expansion and good aeration with the presence of more macropores. However, the massive structure due to high clay percentage in lower horizons would be an obstacle for root growth, as well as prevent drainage contributing to a lack of aeration. The fluctuation of the water table would mean that plants would occasionally be in completely saturated conditions which would restrict their access to oxygen and limit growth. The pH throughout the soil profile is mostly lightly acidic which is a condition that many plants can thrive in. The high CEC, particularly in the upper horizons would indicate that the soil has a good ability to store plant-available nutrients which would benefit their growth, however, it may also indicate that the soil is prone to leaching.

AbigailBrown (talk)18:51, 3 April 2020

a)Gleysolic order, Bg diagnostic horizon

b)Well, the Goose soil has very low sodium content throughout its layers. The presence of a semi-thick Ah layer would be good for some plants, but this environment seems like it would largely make growth difficult for plants. To start, we have multiplegleyed horizons, implying spells of intense anaerobic conditions. Nd All layers below the Ah have a high percentage of clay and therefore micro pores. The small pore size and massive structure will make water extremely difficult for plant roots to access, as is borne out in our data for Goose.

That's all for me! Look forward to corrections and other peoples' responses :)

JacobBeauregard (talk)18:55, 3 April 2020

a) Gleysolic order. Diagnostic horizon: Bg, BCg, Cgk. b) Some advantages of this soil order is that it has a high CEC, which means it can store large amounts of nutrients. It also has a pH that lies within the 6-7 range for optimal plant growth. It also has a 5 cm thick LFH, indicating that there is a good source of organic residues providing nutrients into the soil.

   Some disadvantages of this soil order is its extremely high clay content. This will create very poor drainage conditions in the soil, leading to poor aeration that will inhibit plant growth. Also, the lower horizons have a low Ca:Mg ratio, which is bad for plant growth. The structure of the lower horizons are massive, which also causes extremely poor aeration, and is hard for plant roots to penetrate.

Generally, the top 20 cm of this soil are suitable for plant growth, but below that is extremely unfavourable.

BlaiseMatlock (talk)22:51, 3 April 2020

Good start. When answering this type of question (in general) consider clearly separating your advantages from your disadvantages (e.g. two bullet lists)

SandraBrown (talk)02:47, 4 April 2020

a) Goose soil belongs to Gleysolic Order. The diagnostic horizon is Bg.

b)advantages: because silt and clay accounted for the large proportion of soil texture, Goose soil would have high water retention. Then organic matter would form soil aggregates to retain nutrients. High CEC which give the soil high buffering capacity, if there is acid rain the soil would not much affect. Soil pH is neutral.

disadvantages: soil contains small percentages of sand and high percentages of clay would cause low infiltration, poor drained.

I am not sure about how does Ca, Mg, K, Na influence plants grow. They provide nutrients, but high Ca would cause phosphorus deficiency in soil. While, high Ca exchangeable cations can exchange more nutrient? Also, if the roots are abundant in A horizon does it means the soil has a low decomposition rate? I checked the note of soil structure where can i find more details.

YimingRen (talk)20:21, 4 April 2020

Yiming, consider how soil properties, such as texture and structure change with depth (as well as root abundance).
With respect to P fixation, consider pH (not just Ca).
Ca, Mg, K are all essential plant nutrients. Na is only an issue if levels are high (i.e., sodic soil)
High root abundance does not suggest slow decomposition, but good plant growing conditions.

SandraBrown (talk)04:33, 5 April 2020

a. Goose soil is a gleysol, as diagnosed by the Bg horizon, and the fact that gleying is a dominant process in the soil from 15-55+ cm. b. . i. Advantages: good supply of organic matter, close to neutral pH, high concentrations of base-forming cations, structure above 25cm conducive to plant growth. ii. Disadvantages: poor drainage (as indicated by the fact that it is a gleysol, and the fact that it has massive structure), unfavourable ratios of Ca:Mg:K:Na, poor texture for plant growth, poor structure for plant growth below 25cm.

SpencerShields (talk)01:08, 28 April 2020

Yes, this is a Glesyol... and yes its diagnostic horizon is Bg (and gleying is also evident in ABg, BCg, Cgk)

Everything Spencer that you listed is correct, but for the full mark the explanation would need to be included too. For example, consider elaboration of the following :

  • -what are implications of good organic matter content? In other words, what other soil properties are impacted by high organic matter?
  • -what are implications of neutral pH?
  • -why is structure above 25cm in this soil conductive to plant growth? In what way?

Once again, what is listed is all correct, but elaboration/explanation is needed.
What is missing is mention of the fine texture, including a very low sand content. Then elaboration would be needed to explain what are consequences for other soil properties of such type of texture

MajaKrzic (talk)01:20, 28 April 2020