Does DTPA-TEA method equally extract irons in both ferrous and ferric states? I thought it could explain the low Fe in Bf and Bhf of Podzol if DTPA-TEA method favors extracting ferrous states, assuming Fe in Podzolic B is predominantly in ferric state.
Good question. And yes, DTPA-TEA method does extract bot ferrous and ferric Fe forms, since both of them are plant-available forms.
OK. Thank you, Maja! I think I'm going to figure out something else...
But if the DTPA-TEA extracts both, low Fe in Podzol B cannot be explained like this.
I'm kind of looking at this by the opposite way. Fe in the Podzol B appears relatively low because most of other mineral soils have very high Fe. Crescent, Delta, Ladner soils are underlain by rocks containing a high concentration of sulfide minerals which most likely is composed of pyrite. The oxidation of pyrite increases Fe2+ in soil solution which is further oxidized to become Fe3+ both of which are extracted with DEPA-TEA, which can also explain why Gleysol in this area is so acidic in natural conditions.
But, also, I think Fe2+ and Fe3+ well-solubilized by DOM are lost from Podzol B by lateral seepage during the wet season. As for the Podzol Ap, I think some disturbances after the clearing of original forest increased Fe content.
It just dawned on me that Monday (November 13) is a holiday (in lieu of the Remembrance Day), so I'm happy to extend your deadline for the soil chemistry report to Nov 13 by midnight.
Also, I will not be done with marking of lab #7 assignments until Sunday morning, so that is another reason for this additional deadline extension.
Q. Is it okay to use only one pH value (eg. measured in CaCl2) and one organic matter value (eg. oven dried) for each sample in our analyses?
A. Oven-dried value for soil organic matter is the correct value to use when reporting on soil organic matter. You were give the air-dry values so that you can determine the difference between the 2 set of values which would then allow you to comment on the hygroscopic water content.
As for 2 sets of soil pH values, you can use one of them, unless you want to discuss the difference between two sets of pH values (similar to last week's assignment).
Hi Maja, What is the unit of t electrical conductivity that we got in the last week? Should we do some calculations of the data or we just put our data directly? Thanks for your reply.
In the instruction PDF for the chemistry section summary, it says "... using ALL the data ..." Does this mean we are expected to use the phosphorus, EC, and metal contents data (DTPA-TEA) too? I was wondering this since the weekly assignments did not include the interpretation of these data.
Yes, Taku you should use those data too.
The weekly assignment did not include that data to shorten that last weekly assignment and allow you more time to work on the summary chemistry report.
I was wondering if you would consider forage grass as the same land-use as potatoes/onions. Like is it still considered agriculture land? and if it is, would a forage grass site not experience as much human management compared to the onions/potatoes which may require more management?
It said we should consider 13 samples as mineral soil or organic soil. Can we group Podzol and Solonezt together as mineral soil even they are different soil types?
I was just wondering how you determined the soil order of the 13 soil samples if the tables didn't show what order they belonged too?
I look into the background information of 13 samples. Some tell me soil orders but some not. I think the features of soil which provied by background information and connect them to the features of basic 10 soil orders, then I can figure out which order the sample belongs to.
Anyone else have ideas as to why we chose loss on ignition method? I could only come up with it being potentially cheaper than dry combustion since a special induction furnace isn't used and it can be safer than wet combustion since acids are not used.
I'm thinking maybe the product of ash that can be used for elemental analysis might be a bonus but I'm not 100% sure. If any of you have any other ideas I'd love to hear them! thanks!
Hi everyone, I just put all crucibles and Al-boats in 3 desiccators, which are now placed next to 2 balances in MCML102A lab. You can come at any time after 9 am either tomorrow (Nov 2) or Friday (Nov 3) to weight your sample.
Once you are done weighing, discard your soil samples into one of collection bins in MCML102A
When taking samples out of desiccators, pls be careful not to spill your sample over other samples
Hello, I don't understand what exactly we need to compare in question 2.b. It says "differences in pH values obtained by the two methods". Do we need to subtract pH (water) from pH (CaCl2) and compare these differences to organic matter content?
Yes, that is exactly it. And in the discussion to accompany that comparison, you should explain why certain samples have quite a large difference between pH values determined in water and in a salt (CaCl2) and others don't. Also, what does that difference tell us about soil's capability to resist pH change when we add bases (eg lime) and acids (eg N-fertilizers) to the soil.
Dear Maja, I am confused about the features of oven-dry organic matter content. Is there any relationship between the exchangeable Al charge and oven-dry organic matter content?
Not sure to what question in lab assignment #6 are you referring to? <dr> Here are some notes re. soil organic matter, its determination, and charge formation:
Soil organic matter content is determined by drying in a muffle furnace (not oven) and that is one of the methods of determining soil organic matter. Furthermore, soil organic matter is one of the soil components that carries quite a bit of charge, but Al is not part of structure of organic compounds. Charge on organic compounds is formed on functional groups (eg carboxyl and OH groups) and type of charge (ie negative, positive or none) is driven by pH of soil solution that surrounds organic compound in question.
The difference of value between two methods and oven-dry organic matter content. I think some components of organic matter will volatilize during oven-drying. How oven-dry organic matter content relate to the difference of value between two methods? And the difference of value should be the concentration of H charges or the number of PH?
Question #1 in the lab assignment #6 is asking to "... compare the two sets of values for soil pH and explain the differences in the values obtained by the two methods." Hence, two sets of values that should be compared are soil pH determined in water and soil pH determined in a salt (ie CaCl2).
As for determining soil organic matter by loss on ignition method, the basis for that method is that ALL organic compounds are burnt off at the temperature of 600C.
Soil pH determination is done on air-dried samples (as is the typical procedure in preparing samples for soil chemical lab analyses), not on oven-dried samples.
Dear Maja In Question #2 b), it uses oven-dry organic matter content.Why use oven-dry organic matter not air-dry organic matter?
In Friday's lecture, I explained the reason why soil organic matter determined by the loss on ignition method on air-dried samples needs to be corrected. Please take a look at the lecture notes for last Friday (Oct 26) that are posted in Connect.
There are a couple of texture data that add up to be greater than 100%. I was wondering if they were typos? Or, am I missing something... Podzol, alder forest, Cg => 102% Podzol, cultivated mid slope, C => 101% Gleysol, Delta, 7.5-15cm => 110%
In the provided dataset, letters for soil horizon (A, B or C) were not indicated for Chernozem, Gleysol, or Orthic Humic Gleysol. I'm assuming that we can treat the first layer of each soil as A horizon as the instruction says comparison must be made by the horizon. But can we also assume that the deeper horizons as B1 and B2 (or B and C) regardless of possible suffixes? Or do we need to treat them as "unknown" horizon?
Tricky Taku Soil samples may be take either by horizon or depth. This data set combines both approaches. You cannot necessarily assume a depth specific sample corresponds to a single horizon. You are correct that you should not lump horizons when analyzing soils data. For the specific comparison you have selected, you may either have to compare between horizons or between depths (if horizon information is not given). If you want, tell me the specific comparison you are doing (i.e. the samples) and we can discuss.
I chose the option #2: comparison of different soil orders under similar land uses. For this option, I selected Podzol (UBC farm, cultivated mid-slope), Chernozem (Kamloops, range), Gleysol (Delta, potato cultivation), and Orthic Humic Gleysol (Sumas, Cultivation).
For the purpose of graphing and the convenience of describing the result, I wanted to keep the horizon assigned to each depth for the Podzol at UBC farm, because I've been looking at the change in SOC and bulk density along the depth profile. So I assumed the top layer of the other 3 soils to be an "A" horizon and rest of the depth profile to be B or C based on the general profiles described in the Soil Classification System.
But, now I think I should use only the depth info to compare them by calling them Depth group 1,2,3.... I'm also looking at the texture and aggregate stability, for these, I only use the surface layer... I think I should forget about horizon designation entirely...
Gleysol is soil order (ie the broadest, most general soil classification category), while Orthic Humic Gleysol is the sub-group in Canadian soil classification system.
Classification categories in the Canadian system are (from the most general to the least general): order, great group, sub-group, family, and series.
For example, samples #1 and 6 belong to Gleysolic order, Humic Gleysol great group, Orthic Humic Gleysol sub-group and Delta soil series. Family is typically not specified since it is related to parent material and that info is typically provided in descriptive terms.
Since we define the density of soil extract as 1kg/L in question 3, which density should we use in question 4? Bulk density or 1kg/L? Question 4 is the furrow slice of the soil. It is different between soil extract in question 3 and soil in question 4.
Bill, from question 3 you know the concentration in the soil mg/kg i.e. mg of element x / kg of soil. Question 4 asks you to extrapolate that concentration (mg/kg) over 1 ha area (20 cm deep) assuming a soil bulk density of 1200 kg/m3. Since your answer to question 3 is in mg/kg of soil you need to use the bulk density of the soil in question 4.
In question #3 you need to use density of water for your calculation, but in question #4 you need to consider soil bulk density, since question #4 is asking for re-calculation of element X in the soil.
Question #4 is illustration of the final step in determining how much of an element there is in the soil based on lab analysis. This type of re-calculation is needed to determine application rates of fertilizers or organic amendments.
So, Sandra's explanation above is correct and should be used in dealing with questions #3 and #4.
I am wondering why Mg content is higher in sample 12 (mud bay - saline soil)? Thanks!
Last edit: 22:20, 24 October 2017
Incomplete drainage of mixed tidal waters? Not sure about it.
If data is lacking for a certain soil order/location, can we use data from previous labs of this course to compare? For example, bulk density is missing for UBC Farm - cultivated mid slope in the given data, so could I use the bulk densities we calculated for the UBC farm groups in the earlier labs to compare in the paper? Of course I would state its not the same bulk density but i could say it may be somewhat similar?
sure Matt you could include average data, but just be clear that the data provided includes 2 forest types, and we only sampled 1 BUT you need to be careful - for example the site sampled for bulk density in agriculture had just been cultivated (1st year) and would not be representative. The forest sites were very diverse - the coarse textured site is possibly representative of the Bose soil series but as you saw there was a lot of variability. IF you are comparing Podzols at UBC farm, my suggestion is to use the data provided and draw from what you learned doing your labs in the discussion (rather than using the lab data). Sandra
Then what if the soil series is n.d. do we just describe how that certain soil order would normally be characterized? And are the 2 grass samples included in the agriculture category for comparison?
Hi APBI 403 / SOIL 503 students,
Greetings from Tampa, FL! A birdie told me that some of you might have questions re. how to recalculate concentration of an element in ug/mL to mg/kg.
As you will see in today's lab on available P, and as is mentioned in the preamble for assignment questions 1-4, all standard solutions are made in water. Hence, all these solutions are water-solutions and as such they have the same density as water ... and one can assume that 1L of a water-based solution has mass of 1 kg. Hope this helps
Soil chemistry terminology - Since in soil chemistry we use water-based solutions (as extraction solutions such as ammonium acetate that was used in last week's lab and alos as standard solutions), one needs to assume that these water-based solutions (and extracts of elements obtained by using those extraction solutions) have the same density as water. Consequently, it is to be assumed that 1 mL of a soil extract is equal to 1 mg.
Thus in question 3 "extract 5 mL of soil with 25 mL of extraction solution" remember that we use water-based solutions for extracting our samples.