Post Midterm Flashcards
what are some examples of pedogenic processes?
Additions (humification)
Losses (Leeching of nutrients off site, wind erosion)
Transformation (Chemical changes like hydrolysis and oxidation)
Translocation (elluviation)
What are pedogenic processes?
When material in the horizons is differentiated from the parent material
What is the diagnostic horizon?
Specific sequence of horizons used to classify soils
what is the diagnostic layer in podzols?
Ae horizon (acidic, coarse textured material)
What is the diagnostic layer in luvisols?
Bt - secondary clay enrichment in B horizon from weathering of A
- fine textured parent material
- shiny surfaced peds
What is the diagnostic layer in chernozems?
Thick Ah over Bm (grassland)
Diagnostic layer of a brunisol?
Ah over Bm in a forest ecosystem
what is the dominant differentiating factor in soil horizons?
Color
what are some forms that horizons take when they join?
Smooth
Wavy
Irregular
Broken
What do red colors indicate in soils?
Presence of Fe and good aeration/drainage
-except mottles which are detrimental to drainage
Briefly describe oxidation and reduction reactions
Oxidation - loss of electron(s)
Reduction - Gain of electron(s)
What is chelation?
Movement of organic material from A into B. Facilitated by Ligans.
what are ligans?
Organic compounds that pick up Fe+ or Al+ as it translocates downward through A horizon. They are then deposited in B.
What are ligans called when they attach to Fe+ or Al+ oxides?
Chelates
what nutrients would you expect in acidic soil?
poor nutrients (due to low availability)
what kind of nutrient availability would you expect in basic soil?
High nutrient availability
why are nutrients less available in acidic soils?
Nutrients are stored in the net negative charge of the colloidal fraction. When soil is acidic, high concentrations of hydoxyl (OH) and hydronium (H30) displace nutrients from their receptor sites in the colloidal fraction resulting in leeching of nutrients off site.
What are mottles?
Spots or blotches that differ from the background color. Caused by reduction reactions that happen due to flooding and saturated condition for periods of time. More frequent in fine textured soil.
What 3 parameters is the Munsell color notation based on?
hue - dominant spectral color
value - brightness of color
Chroma - strength of color
What are the two ends of the munsell color notation?
10R- strongest
5Y weakest
What is gleying? What color is gleyed soil?
Gleying refers to prolonged saturation.
Grey/Blue in color
How does soil structure “develop”
Through addition of…
- organic matter from above
- supplemental clays from above
- fe+ al+ oxides from above
- salt from below (upward translocation)
Describe upward translocation
In warm climate with salty soils, upward translocation occurs through the process of evaporation by which water molecules evaporate and rise through soil. As they do they translocate dissolved salts and minerals upwards where they are deposited in the soil
What things effect soil drainage?
Slope Slope position Texture Depths of soil Water table Field capacity Infiltration capacity
What is mottling?
How are Mottles defined?
Blotchy color condition in soil that indicates poor drainage. Caused by reducing conditions and seasonal flooding/saturated conditions
Defined in terms of abundance, size, color, color contrast to the matrix.
What quality can drastically effect the color of a soil?
Moisture
When recording soil color in the field its relative moisture level should also be recorded.
What can color tell us about a soil?
- ease of gas/water exchange
- extent of chemical weathering
- presence of organic material
- soils overall productivity
Soils color changes over time as it develops from the usual dark grey parent material into a variety of other Colors. What factors determine how soil color develops?
- Parent material type
- % organic matter content
- The amount of eluviation/illuviation that has occurred
- The extent of oxidation or reduction reactions and the amount of accumulated oxides in soil
What do red Colors indicate?
The presence of Fe++ or ferrous compounds
Usually means good aeration and drainage
What do yellow Colors indicate?
Intermediate aeration
What do blue and grey Colors indicate in a soil?
Gleying. Indicate poor aeration, drainage and presence of Fe+++
Reducing conditions due to anaerobic bacteria
Fine textured soils
Saturated for prolonged periods
What 3 parameters did munsell break color into
Hue, Value, Chroma
What 5 Colors does the munsell system recognize?
What are these collectively referred to as?
HUE
- red
- yellow
- green
- blue
- purple
What is the brightness of of a color referred to as?
What is the scale?
Value
0-10
What is the measurement of a Colors purity referred to as?
What’s the scale?
Chroma
0-12
How are Colors described in the munsell system?
1-Hue
2-Value
3-Chroma
What is gleying?
What causes it? Describe the process.
Gleying is the extreme outcome of reduction reactions associated with anaerobic bacteria. They use electrons from Fe++ for energy and create Fe+++
Develops a blue grey color
Usually saturated for prolonged periods
Generally fine texture
What order do blue grey soils belong to?
Gleysolic order
How are horizon boundaries differentiated?
Distinctiveness
Form
What is particle density?
Elaborate
Dp - defines the mass of a unit volume of oven dried soil, pore space EXCLUDED.. Sandy soils tend to have a higher Dp than fine textured soils due to their high silicate RFM content and metal content.
Define Bulk Density
Defines the mass of a unit volume of soil, pore space INCLUDED. Sandy soils have a high Db but low pore space. Fine textured soils have a low Db but a high pore space due to the development of secondary particles with internal pore space.
What soil characteristic does bulk density most effect?
What is this quality critical to?
Pore Space
-high db = low pore space
Critical to root growth and development
aeration
drainage
Soil Porosity
What is it?
Which soils would you expect to have a high/low pore space and why?
How does depth effect pore space?
- The percent volume of a soil that is pore space
- Fine textured soils tend to have higher porosity than coarse soils and develop peds more readily.
Since Bd increases with depth, pore space tends to decrease due to compaction the deeper down the soil is.
What is a forestry practice that could increase Db in an area?
Ground harvesting with a skidder. Especially in finer textured soils but noticeable in all. Effect is exaggerated when soil is wet. The compaction is not limited to the skidder trails, which effect large areas of land around them.
Name some factors that contribute to the development of soil structure.
- Organic matter
- Oxides of iron and aluminum
- supplemental clays
- salts
- Expansion and contraction of high clay soils as a function of wetting and drying.
What is the soil order associated with columnar structure development ?
Solonetzic soil
What are some common soil structures?
Granular - common in the upper soil profile where organic matter accumulates
Prismatic - Common in clay soils that experience annual wetting and drying
Blocky - Coarse textured sandy soils cemented with oxides of Al/Fe
Platy - compacted soils (basal tills)
Single Grain-Sandy soils
Massive- No visible structure, very large clods
Columnar - develops in dry environments where mass evapotranspiration leads to column formation.
How is bulk density calculated ?
expressed in g/cm3
Bd is calculated by dividing the grams of oven dried soil by the volume that it fills.
ex. If 50 ml of soil is weighed at 61.5g then the Db would be 61.5 / 50
How is Particle density calculated?
By adding a given weight of oven dried soil to water and recording the volume that is displaced. This volume theoretically depicts the space that would be taken by the soil particles, negating the pore space. You then divide the oven dried mass of the soil in grams, by the volume of the soil particles that was calculated by the water displacement.
what is the equation for percent porosity ?
%porosity = 100-(Db/Dpx100)
what are the respective sizes of gravel, cobble and stones?
Gravel : 2mm - 7.5cm
Cobbles : 7.5cm - 25cm
Stones : everything > 25 cm
What characteristics can be used to differentiate parent material ?
- presence of CFC
- shape of CF
- whether CF is stratified or homogenous
- soil texture
- color
- topographic characteristics of surrounding landscape
All of the above are a process of weathering mostly by running water and gravity
How does physical weathering in increase the rate of chemical weathering?
By increasing the surface area so that more area is available for chemical weathering to occur
What two broad groups can parent materials be classified into?
Sedentary (in situ)
Saprolites
Transported Fluvial Lacustrine Marine Tills Etc
Describe residual parent material
Material that has been produced from on site weathering of rock substrates.Usually very thin soils. Usually found in warmer tropical climates but can be found in rocky outcrops in bc
What’s is colluvial material?
Parent material produced by gravity and differential cooling and heating of mountainsides and scree slopes.
Very sharp angular edges produced by the shattering of rock
Mildly stratified due to heavier rocks being deposited on a lower slope position
Good for road building but bad for plant growth.
What is fluvial material?
Parent material that has been weathered and deposited by running water. It has a stratified structure due to heavier content being deposited lower than fine textured light material.
The stratified structure comes from the various periods of deposition and erosion that take place over time as water channels velocity and depths constantly change.
CFC Material is well rounded from constant tumbling action.
Flat external appearance and found near rivers
What is Lacustrine material?
Parent materials that accumulate at the bottom of lakes ad they are transported into the lakes by faster running channels.
No CFC
Thin, stratified layers due to seasonal changes in deposition (clays deposited in winter when water is at its slowest)
Tend to be flat and lie in depressions in the landscape
Can be good for growing trees if well drained
What is marine material?
A parent material containing gravels, sands and silts or clays deposited in an ocean environment. Usually lie at a gentle angle (3-5 degrees)
Usually in close proximity to oceans and can contain she’ll fragments or calcium carbonates.
In bc can be found within 90m of shoreline
What is moraine material?
A type of parent material that includes basal and ablation tills.
Basal tills are material that has been scraped off the earth by moving glaciers and compacted under them as they advance.
Made up of homogenous clays sands and silts with random CFCs throughout.
Have not been altered by pedogenic processes and are very compacted
Excellent substrate for forest growth
What are glaciomarine deposits?
Fine textured material that contains unstratified coarse fragment that dropped from melting icebergs that broke off the main glaciers.
What is glaciolacustrine material?
Produced primarily of silts that were deposited in giant water bodies that were formed and dammed by glaciers.
Often terraced due to this damming process
What is Glaciofluvial material?
Alluvial material that has been deposited in a glacial environment such as eskers and melt water channels. Can be differentiated from fluvial in that the CFCs are more angular due to being weathered by running water for shorter periods of time.
What is Eolian material
P Material deposited by wind, also known as loess. Generally consist of Sands and silts that are well sorted and poorly compacted.
May take dune like shapes
Can be found around PG in BC
