Exam 3 Flashcards by Jacob Lawson

What is a soil colloid?

Particles with a
diameter of 0.1 to
0.001µm (10,000µm=1cm)

How well did you know this?

Not at all

Perfectly

What are colloids characterized by?

– Their small size (diameter of 0.1 to 0.001µm)
– High surface area with some internal surface area
– Surface charge
– Adsorption of cations and/or anions
– Adsorption of water

How well did you know this?

Not at all

Perfectly

What are Inorganic colloids?

– Clay minerals
– Hydrous oxides
– Are usually crystalline
– Usually make up the bulk of soil colloids.

How well did you know this?

Not at all

Perfectly

What are Organic colloids?

– Highly decomposed organic matter called humus.
– Generally, have a greater influence on soil properties per unit weight than the inorganic colloids.

How well did you know this?

Not at all

Perfectly

What are phyllosilicates?

layered silicate structure

How well did you know this?

Not at all

Perfectly

What are tetrahedral sheets made from?

Si^4+ and O^2- (Si is bonded to 4 Os)

How well did you know this?

Not at all

Perfectly

What are Octahedral Sheets made from?

Al^3+ and O^2- (Al is bonded to 6 Os)

How well did you know this?

Not at all

Perfectly

What is a 1:1 type mineral?

kaolinite (one tetrahedral to one octahedral sheet)

How well did you know this?

Not at all

Perfectly

What is a 2:1 type mineral?

Illite (two tetrahedral to one octahedral sheet)

How well did you know this?

Not at all

Perfectly

What are some characteristics of Iron & Aluminum colloids?

Common in highly weathered soils (like the
Oxisols).
Low cation exchange capacities.
Non-expansive clays.

How well did you know this?

Not at all

Perfectly

Highly weathered = more _______?
Little weathering = more ____?

more oxides, more 2:1 type clays

How well did you know this?

Not at all

Perfectly

A 1:1 phyllosilicate clay has:
a) 1 tetrahedral sheet to 1 octahedral sheet
b) 2 tetrahedral sheets to 1 octahedral sheets
c) 1 oxygen to 1 silicon
d) 1 aluminum to 2 oxygen

a) 1 tetrahedral sheet to 1 octahedral sheet

How well did you know this?

Not at all

Perfectly

What is soil organic matter made of?

Humus, Living, Fresh Residue, and Active Fraction

How well did you know this?

Not at all

Perfectly

What is Anion exchange capacity (AEC)?

sum of total anions that a given soil can absorb

How well did you know this?

Not at all

Perfectly

What is Cation exchange capacity (CEC)?

sum of total cations that a given soil can absorb

How well did you know this?

Not at all

Perfectly

What is Isomorphic Substitution?

process in which one element substitutes another of comparable size in the crystalline structure. Permeant charge.

How well did you know this?

Not at all

Perfectly

What is the isomorphic substitution for 1:1 clay?

Mg substitution for Al in the octahedral lattice
Si2O3OHO2Al2(OH)3 →Si2O3OHO2AlMg(OH)3

How well did you know this?

Not at all

Perfectly

What is the isomorphic substitution for 2:1 clay?

2:1 Clay (e.g. montmorillite)
– Mg substitution for Al in the octahedral lattice
– Al substitution for Si in the tetrahedral lattice
Si2O3OHO2Al2OH2 Si2O3 → Si2O3OHO2AlMgOH2SiAlO3

How well did you know this?

Not at all

Perfectly

What is a Milliequivalent (meq)?

one milligram of hydrogen or the amount of any other ion
that will combine with it or displace it.
Equivalent weight = molecular wt (g)/ valence or charge

How well did you know this?

Not at all

Perfectly

What is CEC expressed in?

milliequivalents

How well did you know this?

Not at all

Perfectly

What is Flocculation?

– individual particles stick together to form aggregates of particles or floccules. Such aggregates do not move in the soil solution and form the basis for soil structure.

How well did you know this?

Not at all

Perfectly

What is Dispersion?

aggregates do not form. Each particle behaves as an individual.
– Without aggregation, water, air, and root movement in the soil is inhibited.
– Dispersion is not a desirable characteristic of productive soils.

How well did you know this?

Not at all

Perfectly

In a 1:1 type phyllosilicate clay, what cation is replaces the aluminum, and what sheet is
it replaced on?
a) Mg2+, the tetrahedral sheet
b) Mg2+, the octahedral sheet
c) Si4+, the tetrahedral sheet
d) Si4+, the octahedral sheet

b) Mg2+, the octahedral sheet

How well did you know this?

Not at all

Perfectly

What soil pH has the highest cation exchange capacity (CEC)?
a) pH 4
b) pH 5
c) pH 6
d) pH 7

d) pH 7

How well did you know this?

Not at all

Perfectly

What type of clay will have the highest cation exchange capacity (CEC)? a) 1:1 type b) 2:1 type c) Iron oxides d) Aluminum oxides

b) 2:1 type

Metals such as Fe, Mn, Cu, and Zn can be toxic to plants at __ pH

low

When going from a pH 5 to a pH 6, the pH 5 soil has how much more acidity? a) 1 b) 10 c) 100 d) Cannot be determined

b) 10

What are the 5 sources of acidity?

* Reaction of CO2 from atmosphere with the soil solution: CO2 + H2O <--> CO3^2- + 2H^+ * Uptake of basic cations and excretion of H+ – Charge balance must be maintained. * Decomposition of organic residues. * Oxidation of NH4^+ to NO3^- by microbes (manures and ammonium-based fertilizers). * Aluminum hydrolysis form Al-hydroxides and H+ ions: (oxidation of Al^3+ to Al(OH)3)

What characteristics of soil has the greatest buffering capacity?

– High clay – High organic matter

What characteristics of soil has the least buffering capacity?

– Low clay – Low organic matter

What soil texture has the lowest buffering capacity? a) Sand b) Silt c) Clay d) Organic matter

a) Sand

Oxisols are _____ acidic than Ultisols which are ____ acidic than Alfisols

more,more

What are the steps in the lime reaction

1. Ca2+ from the lime replaces Al3+ and H+ on the cation exchange complex. 2. The carbonate reacts with the H+ ions, removing them from solution thereby raising the pH. (turning H+ into water) 3. Al3+ is hydrolyzed to form Al-hydroxides and H+ ions, Carbonate from the lime neutralizes the H+ generated during the Al-hydrolosis (step 2 again)

What is the Lime recommendation Model?

Lime Req. (t/ac) = ((target pH - current pH)/(6.6 - current pH)) * Exchangeable acidity (AC)

What is the equation for Exchangeable acidity (AC)?

𝐴𝐶 = 4 × (6.6 − 𝑏𝑢𝑓𝑓𝑒𝑟𝑒𝑑 𝑝𝐻)

What is the difference between Calcitic limestone and Dolomitic limestone?

Calcitic limestone has calcium carbonate and Dolomitic limestone has calcium & magnesium carbonate

What is Calcium Carbonate Equivalent (CCE)?

Neutralizing value of any liming material compared to pure calcium carbonate (CaCO3)

What soil texture needs the most amount of lime to change the pH from 4 to 5? a) Gravel b) Sand c) Silt d) Clay

d) Clay

How many essential elements do plants need to complete their life cycle?

What are the structural elements?

Carbon, Hydrogen, and Oxygen

What are the Primary Macronutrients?

Nitrogen, Phosphorus, and Potassium

What are the Secondary Macronutrients?

Calcium, Magnesium, and Sulfur

What are the micronutrients?

Iron, Manganese, Boron, Zinc, Copper, Chlorine, Molybdenum, and Nickel

What is Mass Flow?

dissolved nutrients move to the root in soil water that is flowing towards the roots

What is Diffusion?

nutrients move from higher concentration in the bulk soil solution to lower concentration at the root

What is root interception?

roots obtain nutrients by physically contacting nutrients in soil solution or on soil surfaces.

What plant element is needed in the largest quantity? a) Hydrogen b) Carbon c) Oxygen d) Nitrogen

b) carbon

What are the structural components of plant? a) Hydrogen b) Carbon c) Oxygen d) All the above

d) All the above

When plant nutrients move along a concentration gradient, it is called what? a) Root interception b) Mass flow c) Osmosis d) Diffusion

d) Diffusion

Which of the following nutrient are beneficial but not essential? a) Boron b) Chlorine c) Sodium d) Nickle

c) Sodium

What are plant-available forms of Nitrogen?

Nitrate (NO3^-), Ammonium (NH4^+)

How can Nitrogen can be fixation?

Legumes, Bacteria, N2

What is mineralization?

Biological conversation of unavailable organic N into plant available inorganic N, Organic N to ammonium to nitrate (ammonification then nitrification)

What is Immobilization?

Biological conversation of plant available N into unavailable organic N

What factors favor Ammonification?

Warm temperatures, good soil moisture, and Adequate supply of O2

What factors favor Ammonification?

Well drained soils, warm temps, an acidifying process, and lack of pesticides

What is denitrification?

Transformation of NO3^- to N2, N2O or NO gases.

What are the conditions that denitrification occurs at?

--Under low oxygen (anaerobic) conditions, – Under warm conditions – Where there is readily available source of organic matter for microbial energy source.

What process converts organic N is converted to inorganic N? a) Volatilization b) Mineralization c) Immobilization d) Fixation

b) Mineralization

When soil bacteria turn atmospheric nitrogen to plant available forms of nitrogen, it is called what? a) Fixation b) Volatilization c) Immobilization d) Denitrification

a) Fixation

Explain the Phosphorus cycle

The phosphorus cycle is mainly based on equilibrium chemistry (very little available about 4 ibs/ac) with Phosphorous cycling between Stable, unavailable organic P to soil solution, available P to Stable, unavailable inorganic P

How does pH affect phosphorus in the soil

Acidic soil will make the unavailable bubble more inorganic, Fe and Al oxides can affect phosphorus. most available at 6.5

What are the plant available forms of P?

H2PO4^- and HPO4^2-

What are environmental issues relating to P?

The large use of P from fertilizers from swine and poultry is used on fields that over saturate soil. Phosphorus additions to natural waters can cause eutrophication (algal blooms)

Which plant nutrient leaches the fastest through the soil? a) Nitrogen b) Potassium c) Calcium d) Phosphorus

a) Nitrogen

Which plant nutrient leaches the slowest through the soil? a) Nitrogen b) Potassium c) Calcium d) Phosphorus

d) Phosphorus

Sulfur is considered: a) Structural component b) Macronutrient c) Micronutrient d) Not essential but beneficial

b) Macronutrient

Plant micronutrients include: a) Carbon b) Potassium c) Iron d) Sulfur

c) Iron

Which of the following plant nutrients are only in anion form? a) Potassium b) Phosphorus c) Carbon d) Nitrogen

b) Phosphorus

What does 10-10-10 mean?

10% N, 10% P2O5, 10% K2O (NPK)

A bag of fertilizer contains 5-10-15. How much phosphorus is in the fertilizer for every 100 lbs? a) 5 lbs b) 10 lbs c) 15 lbs d) Cannot be determined with the data

b) 10 lbs

A bag of fertilizer contains 5-10-15 and we’ve determined it has 10 lbs phosphorous. What form is the phosphorus in? a) Elemental P b) P2O5 c) H2PO4^- d) HPO4^2-

b) P2O5

What type of clays do Mollisols/Histosols, Alfisols, ultisols, and oxisols have?

Mollisols/Histosols have mostly 2:1 type clays, Alfisols have a mix of 2:1 and 1:1 type clays, Ultisols have moslty 1:1 type clays, and oxisols have mostly Fe, Al oxide clays

What is pH dependent charge?

Broken ends of clays carry a charge. Charge can change based on the pH. Lower pH = more H+ will attach to the broken ends (aka more positive).

What is Active acidity?

H+ or Al3+ in the water of soil and a measure of how acidic the soil is.

What is Exchangeable acidity?

H+ and Al3+ that are on exchange sites of clay or OM negative sites.

What is Residual acidity?

H+ or Al3+ that are bound to clay or OM and NOT exchangeable.

What are the bacteria that drive nitrification?

Nitrosomonas, Nitrobacter

What are the main questions to ask about nutrient management?

Amount?, Timing?, Source?, Placement?

What depth should you sample soil for field crops?

collect samples to the same depth that the field is plowed (usually about 8 inches)

What depth should you sample soil for perennial crops?

samples taken to a depth of 4 inches will best represent the crop’s lime and fertilizer needs.

The lower the cation exchange capacity of a soil, the higher is its buffer capacity. (T/F)

False

Which of the following is not a characteristic of soil colloids? A. electronegative charges B. ability to exchange ions with the soil solution C. low water holding capacity D. high external surfaces E. very small size

C. low water holding capacity

A 2:1 type silicate clay has one octahedral sheet sandwiched between two tetrahedral sheets. (T/F)

True

The acidity of "acid rain" can be partially traced to the reaction of CO2 in the atmosphere forming carbonic acid (H2CO3). (T/F)

True

Iron and aluminum hydrous oxides are characteristic of soils that are highly weathered chemically. (T/F)

True

The higher the cation exchange capacity of a soil, the greater is its buffer capacity. (T/F)

True

Humus has a much higher cation adsorption capacity at pH 5.5 than at pH 8.0. (T/F)

False

How does the amount of lime needed to neutralize the residual acidity in a clay loam soil compare to that needed to neutralize the active acidity in that soil? A. Residual requires 5,000 times greater. B. Residual requires about the same. C. Residual requires 10 times greater. D. Residual requires considerably less. E. Residual requires about double.

A. Residual requires 5,000 times greater.

Among the soils of which order would you most likely find the highest buffering capacities? A. Alfisols B. Oxisols C. Ultisols D. Spodosols E. Vertisols

E. Vertisols

The high cation adsorption capacity of a 2:1 clay is due primarily to the substitution of silicon atoms for aluminum in the tetrahedral sheet. (T/F)

False

Most micronutrients play essential roles in plant metabolism as enzyme activators. (T/F)

True

The conversion of plant-available forms of nitrogen into microbial or plant biomass is an example of mineralization. (T/F)

False

Plants can only obtain nitrogen from the soil by taking up soluble anions. In general cations can not be absorbed by plants. (T/F)

False

To be practical, a nitrification inhibitor should kill or inhibit ________. A. Nitrosomonas B. Nitrobacter C. either A or B D. none of the above

A. Nitrosomonas

Potassium is more readily leached from a neutral sandy soil than from an acid clayey soil. (T/F)

True

Wetlands and forests growing along the banks of rivers remove much nitrogen from groundwater by the process of ________. A. nitrification B. ammonification C. immobilization D. denitrification E. none of the above

D. denitrification

In order for nitrate to form from soil organic matter, ________ must be present in the soil. A. Nitrobacter B. Nitrosomonas C. either A or B D. both A and B E. none of the above

D. both A and B

Most nitrogen leaching to groundwater is in the form of ammonium. (T/F)

False

In what range of soil pH is phosphorus generally most available to plants? A. 4.5-5.5 B. 5.5-7.0 C. >8.0 D. 3.5-4.5 E. 7.0-8.0

B. 5.5-7.0

In most soils, mineralization of soil organic matter is an important source of plant available ________. A. phosphorus B. potassium C. both A and B D. none of the above

A. phosphorus

What soil has the most available phosphorus? Select all that apply. a. Clayey topsoil b. Sandy subsoil c. Sandy topsoil d. Clayey subsoil

a. Clayey topsoil

What soil elements are cations?

Boron (depending on pH), Calcium, Copper, Hydrogen, Magnesium, Manganese, Nickel, Nitrogen (Ammonium form), Potassium, Zinc

Is Boron a Cation or an Anion?

It depends on pH

Is Calcium a Cation or an Anion?

Cation

Is Copper a Cation or an Anion?

Cation

Is Hydrogen a Cation or an Anion?

Cation

Is Magnesium a Cation or an Anion?

Cation

Is Manganese a Cation or an Anion?

Cation

Is Nickel a Cation or an Anion?

Cation

Is Nitrogen (Ammonium form) a Cation or an Anion?

Cation

Is Potassium a Cation or an Anion?

Cation

Is Zinc a Cation or an Anion?

Cation

What soil elements are Anions?

Boron (depending on pH), Chloride, Molybdate, Nitrogen (Nitrate form), Phosphate *, Sulfate

Is Chloride a Cation or an Anion?

Anion

Is Molybdate a Cation or an Anion?

Anion

Is Nitrogen (Nitrate form) a Cation or an Anion?

Anion

Is Phosphate a Cation or an Anion?

Anion (not mobile in high Fe/Al soils)

Is Sulfate a Cation or an Anion?

Anion

Exam 3 Flashcards

(119 cards)