This exam is going to kick my ass (Soils Exam 3)

soil colloids are ____ mm in diameter

0.001

___ ___ are the seat of soil activity

soil colloids

types of soil colloids

layered silicate clays, humus, oxides, amorphous materials

to take into, a sponge

absorption

to adhere to , nutrients and water adhere to soils particles

adsorption

retention of organic compounds by complexing absorption, adsorption, or other means

sorption

approximately the amount of land tillable by one man behind an ox in one day

acre furrow slice

an acre furrow slice is ___ ft x ___ ft ___ in deep

209, 209, 6

an acre furrow slice is _____ square feet x 6 in

43560

the shape of layered silicate clays is ___

platy

size of layered silicate clay materials

internal surface area in layered silicate clays is also referred to as an ___ property

expanding

____ structure in silicate clays have 4 sides

tetrahedron

substitution of Al3+ for Si4+ when it is not present and results in a negative charge

isomorphous substitution

in tetrahedron structure, ___ in the center is surrounded by 4 ___ and is electrically balanced

Si4+, oxygen

tetrahedron has a coordination number of ____

4

____ structure in silicate clays have 8 sides

octahedron

octahedron structure is comprised of a central ___ ion surrounded by __ and __ groups, structure is neutral

Al3+, O and OH

octahedron has a coordination number of ___

6

negatively charged soil colloid

micelle

___ aids in the adsorption of cations and water

micelles

cation exchange occurs on a __ for ___ basis

charge for charge

T/F: there is no change in electrical balance with cation exchange

true

T/F: cation exchange is a part of the clay mineral structure

false

___ and ___ ions are involved with cation exchange

exchangeable and soluble

factors affecting cation exchange

effective size, concentration, valence (charge, and location of the ion

measure of the amount of negative charge the soil has

cation exchange capacity

CEC units are ___ or ___

cmolc kg-1 or me 100g-1

acidic cations

H+ and Al3+

basic cations

Ca2+, Mg2+, K+, Na+ and NH4+

if Na+ fills 15% CEC then the resulting problems are ___, ___ and ___

high pH, dispersion, columnar structure

in acid soils, __ and ___ dominate

H+ and Al3+

in our local soils, ___ and ___ dominate

Ca2+ and Mg2+

measure of the soils ability to hold cations

cation exchange capacity

% of CEC filled with basic cations

base saturation

when soil pH is

7.5, linear

1:1 clay silicate mineral, no shrink/swell, no internal surface area

kaolinite

kaolinite has a __:__ clay

1:1

__ bonds hold sheets together in kaolinite

H

clay: found in old, strongly weathered soils, has low surface area and low CEC

kaolinite

CEC in kaolinite is due to ___ and ___ IS

broken bonds, little IS

T/F: kaolinite can be productive with careful management

true

clay: 2:1 expanding silicate clay, found in young, unweathered soils, key in midwest/northern great plains, volume can increase 2-3X

smectite

smectite has both __ and __ surface area

internal and external

___ clays are very sticky and plastic and high very high shrink/swell

smectite

smectite has ___ CEC

high

____ is not good for roads and buildings

smectite

the charge of smectite is based on ___ in the octahedral layer

IS

surface area of smectite ____

700+ m2 g-1

another name for smectite

montmorillonite

2:1 clay mineral, does not expand, IS substitution in the tetrahedral layers

illite

___ is the clay with the most negative charge

illite

___ bridges hold clay micelles together in illite

K

in illite, NH4+ can replace K+ in potassium bridges causing ___ ___

ammonium fixation

NH4+ and K+ are ____ cations

accessory

surface area of illite _____

100 to 120 m2 g-1

illite is found in the ___

midwest

CEC of illite

20 to 40 me

2:1 clay mineral formed from weathering of illite micas, has internal and external surface area

vermiculite

___ has both tetrahedral and octahedral IS

vermiculite

vermiculite has ____ shrink/swell

moderate

CEC of vermiculite

100 to 150 me

___ ___ is a source of negative charge

isomorphous substitution

in IS, ___ is substitued for __ in the tetrahedral layer

Al3+ for Si4+

in IS, ___ ____ or ___ are subsituted for ___ in the ocahedral layer

Mg2+, Fe2+, or Zn2+ for Al3+

IS is cation for cation based on ___

size

IS occurs when a mineral is ___

forming

IS usually results in a ___ charge

negative

positive soil colloids are ___ and __ oxides

iron and aluminum

___ soil colloids are found in strongly weathered and very acid soils

positive

positive soil colloids have ___ exchange capacity

AEC

factors determining the colloids in soils

PM, pedologic age, climate and vegetation, soil depth, drainage and leaching, weathering

silicate clay weathering model

Primary minerals > mica/vermiculite/illite > smectite > kaolinite > oxides

CEC ____ in old, weathered soils

decreases

AEC ___ in old weathered soils

increases

CEC ___ with an increased pH

increases

AEC ___ with an increased PH

decreases

measure of soil acidity and alkalinity

pH

each step in pH represents a ___ fold change in H+ and OH- concentration

10

pH is a negative log of ___ ion concentration

H

pH range for most soils is __ to __

4 to 8

optimum pH range for crop plants

6.5 to 7.5

pH indicating excess calcium

7.5 to 8.4

pH indicating excess sodium

>8.4

pH indicating very acidic

factors affecting soil pH

OM decomposition, acid rain, other acids, leaching, vegetation, season (summer lower values), management

3 things to consider when liming/acidifying

CEC and PBS needed, effectiveness of materials, methods of application

reasons to lower soil pH

control pests, plant needs

methods of pH determination

water, dyes, paste, salts

___ is the most widely run chemical test on soils

pH

actinomycetes like __ condition

alkaline

fungi like ___ conditions

acid

___ soil acidity is when H+ and Al3+ is in solution

active

___ soil acidity is when CE is released

exchangeable

___ soil acidity is when H+ and Al3+ are bound to clays and OM but are not exchangeable

reserve

all three types of soil acidity have the same ___ of acidic and basic cation but not the same quantity

distribution

as CEC increses, the soils buffering (ability to resist changes in pH) capacity ___

increases

T/F: before pH change can happen, all 3 forms of acidity must be neutralized

true

acid soils have a PBS of

80%

in acid soils, pH 5 to 6.9 __ and __ are dominant

Ca2+ and Mg2+