LE2 Flashcards
1
Q
One of the most variable characteristic of soil
A
Water content
2
Q
The soil acts as a ___________________, making it available for plants as it is needed
A
reservoir for water
3
Q
Soil water is part of what cycle?
A
Global hydrological cycle
4
Q
What factors of soil does water affect?
A
- Soil formation
- Structure
- Stability and Erosion
5
Q
Water causes soil particles to :
A
- Swell and shrink
- Adhere to each other
- Form structural aggregate
6
Q
Water alters the soil profile by?
A
Dissolving and translocating minerals
7
Q
What causes the decrease in soil fertility under extreme rainfall events?
A
Leaching
8
Q
Four reasons why water is essential to plants
A
- It constitutes 85-95% of the plant’s protoplasm
- Essential for photosynthesis
- Solvent in which nutrients are carried to, into and throughout the plant
- Provides turgidity
9
Q
Classifications of Soil Water
Five categories of water surrounding a clay or soil particle :
A
- Adsorbed water (hygroscopic water)
- Water at permanent wilting point
- Capillary water (water at field capacity)
- Gravitational water
- Chemically-combined water
10
Q
It is held in the surface of the particle by powerful forces of electrical attraction and virtually in a solid state of very small thickness
A
Adsorbed water (hygroscopic water)
11
Q
Thickness of adsorbed water
A
0.005um
12
Q
It cannot be removed by oven drying at 110 degrees celsius
A
Adsorbed water
13
Q
Water that can be removed by oven drying but not by air drying
A
Water at permanent wilting point
14
Q
Water that is not so tightly held
A
Water at permanent wilting point
15
Q
Water that is held by surface tension, generally removable by air drying
A
Capillary water
16
Q
Water that is removable by drainage, can move in the voids between soil grains
A
Gravitational water
17
Q
Water that is not of much use to the plants
A
Gravitational water
18
Q
Water that is in the form of water of hydration within the crystal structure
A
Chemically-combined water
19
Q
Water that is not generally removable by oven drying
A
Chemically-combined water
20
Q
What are the qualitative descriptions of soil wetness?
A
- Maximum retentive capacity
- Field capacity
- Permanent Wilting Point
- Available water storage capacity
21
Q
It is a qualitative description of soil wetness when all soil pores are filled with water and becomes saturated
A
Maximum retentive capacity
22
Q
A qualitative description of soil wetness where its matric potential is close to zero and the volumetric water content is essentially the same as total porosity
A
Maximum retentive capacity
23
Q
TRUE OR FALSE
In maximum retentive capacity, the soil will remain at maximum retentive capacity as long as water continues to infiltrate, because water held in the largest pores will percolate downward under the influence of gravitational forces
A
TRUE
24
Q
A qualitative description of soil wetness wherein moisture content of the soil after gravity has removed all the water it can. Usually occurs 1-3 days after rain
A
Field capacity
25
Qualitative description of water wherein smaller pores remain full of water, many of the intermediate pores are partially filled and most of the large pores are nearly empty
**Field capacity**
26
How much suction force must plants exert to obtain water at field capacity?
**1/3 bar**
27
Qualitative description of water wherein it is the soil moisture percentage at which plants cannot obtain enough moisture to continue growing
**Permanent Wilting Point**
28
TRUE OR FALSE
At PWP, water is held -very loosely- by the mineral and particles of the soil
**FALSE**
very tightly
29
How much suction force do plants exert to obtain moisture at PWP?
**15 bars**
30
TRUE OR FALSE
Although not yet dead, plants below PWP cannot recover if water is provided
**TRUE**
31
Qualitative description of soil wetness wherein it is the amount of liquid water stored in the soil and subsequently released for use by the plants
**Available Water Storage Capacity**
32
A qualitative description of soil wetness which varies directly with the total amount of medium-sized pore spaces
**Available Water Storage Capacity**
33
TRUE OR FALSE
In AWSC, pore spaces wider than 10 micrometers drain water readily and pore spaces narrower than 0.2 micrometer release the retained water too slowly
**TRUE**
34
The formula of AWSC
AWSC = FC - PWP
35
What forces allow the water to move through the soil?
- **Gravity**
- **Osmosis**
- **Capillarity**
36
At 0-1/3 bar suction, water moves through soil due to gravity; this is called _______________
**Saturated flow**
37
At higher suction, water movement is called _____________
**Unsaturated flow**
38
Because of the surface tension between water particles, water flows through the ground unevenly called _____________
**Gravity fingers**
39
Factors controlling water flow in the soils
- **Soil texture**
- **Soil structure**
- **Amount of organic matter**
- **Depth of soil to impervious layers such as hardpans or bedrock**
- **Amount of water already in the soil**
- **Soil temperature**
40
TRUE OR FALSE
-Coarse-textured- soils with granular structure are most favorable to infiltration of water
**FALSE**
Fine-textured
41
Three Main Types of Forces which Contribute to the Energy State of Soil Water
- **Gravitational Potential**
- **Osmotic Potential**
- **Matric Potential**
42
A force where water has a positive energy and can flow out of the soil through the large pores
**Gravitational potential**
43
A point when cohesive forces are not large enough to hold onto the water
**Gravitational potential**
44
A force that is only significant when soils are saturated
**Gravitational potential**
45
It is the movement of water from regions of higher potential to regions of lower potential
**Osmosis**
46
Force where its potential is due to the attraction that salts have for water through the phenomenon of osmosis
**Osmotic potential**
47
Force that is attributable to the presence of solutes in the soil solution
**Osmotic potential**
48
TRUE OR FALSE
The greater the concentration of solutes, the lower the osmotic potential
**TRUE**
49
This energy is negative relative to free water
**Osmotic potential**
50
Force wherein water flows from the solution with the lower solute concentration into the solution with higher solute concentration
**Osmotic potential**
51
The potential energy of water attracted to soil solids
**Matric potential**
52
Force that is operational in unsaturated soil above the water table
**Matric potential**
53
TRUE OR FALSE
In a -saturated soil-, matric potential results from the capillarity and adhesion forces
**FALSE**
unsaturated soil
54
TRUE OR FALSE
Plants must overcome the energy of matric potential to extract water from the soil
**TRUE**
55
Tenacity with which soil holds water
**Soil Moisture Tension**
56
TRUE OR FALSE
As soil moisture tension increases, the amount of energy exerted by a plant to remove the water from the soil must also increase
**TRUE**
57
TRUE OR FALSE
Soil moisture tension is negative tension
**TRUE**
58
Two forces that allow water to move through the soil
- **Gravitational forces**
- **Capillary forces**
59
TRUE OR FALSE
Gravitational and capillary forces act simultaneously in soils
**TRUE**
60
Two attractions involved in capillary action
- **Cohesion**
- **Adhesion**
61
TRUE OR FALSE
Capillary forces are greater in -large- pores
**FALSE**
small pores
62
What enables plant roots to make use of water from the wetter portions of the soil profile particularly from a water table
**Capillary movement**
63
Methods to measure soil water content
- **Hand-feel method**
- **Gravimetric method**
- **Electrical Resistance Blocks method**
- **Neutron scattering method**
- **Tensiometer method**
64
Ability of the soil to stick to itself or to other objects and its ability to resist deformation and rupture
**Soil consistency**
65
TRUE OR FALSE
Soil consistency largely depends on soil minerals and water content
**TRUE**
66
Soil physical property which is used in predicting cultivation problems and the ability of the soil to support buildings and roads
**Soil consistency**
67
Three moisture conditions that soil consistency is measured at
- **wet**
- **moist**
- **dry**
68
The ability of the soil material to adhere to other objects
**Stickiness**
69
The ability of the soil material to change shape, but not volume, continuously under the influence of an applied stress and to retain the impressed shape on removal of the stress.
**Plasticity**
70
TRUE OR FALSE
Testing is done when the soil is saturated with water, as, for example, immediately after a good rainfall
**TRUE**
71
Created by Albert Atterberg, a Swedish chemist and were later refined by Arthur Casagrande
**Atterberg Limits**
72
Four distinct states in the Atterberg Limits
- **Solid state**
- **Semi-solid state**
- **Plastic state**
- **Liquid state**
73
In Atterberg Limits, it is the water content of soil in which soil grains are separated by water just enough for the soil mass to loss shear strength
**Liquid Limit**
74
In Atterberg Limits, it is the water content in which the soil will pass from plastic state to semi-solid state
**Plastic Limit**
75
In Atterberg Limits, water content in which the soil no longer changes in volume regardless of further drying
**Shrinkage Limit**
76
In Atterberg Limits, it is the lowest water content possible for the soil to be completely saturated
**Shrinkage Limit**
77
Measure of the plasticity of a soil
**Plasticity Index**
78
It is the difference
between the liquid limit and the plastic limit
**Plasticity Index**
79
a substance microscopically dispersed throughout another substance and have a diameter of between approximately 1 and 1000 nanometers (.000001 m)
**Colloid**
80
it usually consists of the humus and clay dispersed in soil solution
**Soil colloid**
81
Seat of the various chemical reactions in soils (<0.001 mm)
**Soil colloid**
82
Chemical reactivity is due to :
- **Large specific surface area**
- **Presence of electric charges**
83
Types of soil colloids
- **Inorganic colloids (clay)**
- **Organic colloids (humus)**
84
Three most abundant elements in the earth’s crust
- **Silicon**
- **Aluminum**
- **Oxygen**
85
Influence the properties of clay colloids
**Atomic arrangement and composition**
86
Structurally, clay colloids can be grouped into :
- **Crystalline**
- **Amorphous**
87
Composed of sheet-structured aluminosilicates
**Crystalline silicate clays**
88
TRUE OR FALSE
In crystalline silicate clays, each clay type does not occur in pure form in the clay fraction of the soil
**TRUE**
89
Five groups of crystalline silicate clays
- **Kandites**
- **Smectites**
- **Vermiculite**
- **Illite**
- **Chlorite**
90
Have one silicon (tetrahedral) sheet and one aluminum (octahedral) sheet (1:1 type)
**Kandites**
91
TRUE OR FALSE
Kandites are -expanding- clay type
**FALSE**
Non-expanding
92
Most prominent member of kandites
**Kaolinite**
93
TRUE OR FALSE
Kaolinite is the dominant clay mineral in highly-weathered soils
**TRUE**
94
Have one aluminum octahedral sandwiched between two silicon tetrahedral sheets (2:1 expanding type)
**Smectites**
95
Most important smectite member
**Montmorillonite**
96
substitution of one atom by another of similar size in a mineral without disrupting or changing the mineral structure
**Isomorphous substitution**
97
2:1 limited expansion type
**Vermiculite**
98
2:1 non-expanding, sometimes referred to as hydrous mica because it is believed to be the weathering product of mica
**Illite**
99
2:1:1 non-expanding type
**Chlorite**
100
Have properties like those of the silicate clays, except that they do not have silicon as one of the main building blocks
**Crystalline non-silicate clays**
101
Especially important in the more weathered soils of warm and humid regions, such as ultisols and oxisols
**Crystalline non-silicate clays**
102
Usually associated with relatively young soils derived from volcanic ash and characteristically containing high organic matter
**Amorphous silicate clays**
103
Represented by allophane and imogolite
**Amorphous silicate clays**
104
very stable, highly weathered clay colloids so no more nutrients to release in weathering
**Amorphous non-silicate clays**
105
Attributes of organic colloids
- **High molecular weight organic product**
- **Highly charged**
- **Has a large surface area per unit mass**
106
TRUE OR FALSE
Organic colloids are in a dynamic state, always changing
**TRUE**
107
Constituents of organic colloids
- **Fulvic acid**
- **Humic acid**
- **Humin**
108
Physical properties influenced by soil colloids
- **large surface area per unit of mass**
- **plasticity**
109
Chemical properties influenced by soil colloids
- **Sources of ions for plant nutrition**
- **Source of electro-negativity (CEC)**
- **Buffering capacity**
110
General properties of soil colloid
- **Size**
- **Surface area**
- **Surface charges**
- **Adsorption of cations**
- **Adsorption of water**
- **Cohesion**
- **Adhesion**
- **Swelling and shrinkage**
- **Dispersion and flocculation**
111
TRUE OR FALSE
Because of their small size, all soil colloids expose a large external surface per unit mass
**TRUE**
112
The magnitude of the charge is known as
**Zeta potential**
113
TRUE OR FALSE
a colloidal particle is accompanied by a swarm of cations that are adsorbed or held on the particle surfaces
**TRUE**
114
Soil colloidal property that plays a role in the survival of microorganisms, especially bacteria
**Adsorption of water**
115
Phenomenon of sticking together of colloidal particles that are of similar nature
**Cohesion**
116
Phenomenon of colloidal particles sticking to other substances
**Adhesion**
117
TRUE OR FALSE
As long as the colloidal particles remain charged, they -attract- each other, and the suspension remains stable
**FALSE**
Repel
118
A process in which positively charged ions in soil solution leave the solution and attach themselves loosely to the solid phase, which has a net negative charge. At the same time, cations on the solids enter the solution
**Cation Exchange**
119
It is the mechanism of nutrient retention and release in soils
**Cation Exchange**
120
Cations loosely held on the surface of the clay minerals that can be replaced easily by other cations
**Exchangeable cations**
121
Examples of exchangeable cations
**NH4+, K+, Na+, H+, Ca2+, Mg2+, AI3+**
122
It is the water surrounding the soil particles which contain dissolved minerals and salts.
**Soil solution**
123
What are the negatively-charged sites called?
**Cation exchange sites**
124
TRUE OR FALSE
The exchangeable cations are retained in soils and not lost with leaching water
**TRUE**
125
Characteristics of cation exchange
- **Reversible**
- **Stoichiometric**
- **Instantaneous**
126
TRUE OR FALSE
Highly charged cations tend to be held -more loosely- than are those that are less highly charged
**FALSE**
more tightly
127
Cation lyotropic series
**Al3+ > Ca2+ > Mg2+ > K+ = NH4+ >Na+ >Li+**
128
It is the general order of preference of cations in exchange reactions
**Lyotropic series**
129
TRUE OR FALSE
Small cations tend to be held more tightly and are replaced from the exchange complex less easily
**TRUE**
130
TRUE OR FALSE
Regardless of size or charge, cations that dominate or are present in large concentration in the soil solution are favored in the exchange reaction
**TRUE**
131
Cations that is present in very high concentrations in very acid soils
**H+ and Al3+**
132
Dominant cations in neutral to moderately alkaline soils
**Ca2+ and Mg2+**
133
Adsorbed cation in very high quantities in poorly drained arid soils
**Na+**
134
It is the total capacity of a soil to hold exchangeable cations
**Cation Exchange Capacity**
135
CEC is expressed as
**cmolc/kg soil**
136
Earlier unit for CEC
**meq/100g soils**
137
The exchangeable cations of most importance in soil are :
- **Calcium (Ca2+)**
- **Magnesium (Mg2+)**
- **Sodium (Na+)**
- **Potassium (K+)**
- **Hydrogen (H+)**
- **Aluminum (Al3+)**
138
TRUE OR FALSE
CEC is an inherent soil characteristic and is difficult to alter significantly
**TRUE**
139
CEC is used as a measure of the soil’s :
- **Fertility**
- **Nutrient retention capacity**
- **Capacity to protect groundwater from cation contamination**
140
Soil properties that influence CEC
- **Texture**
- **Amount and type of clay mineral**
- **Organic matter content**
141
It is the degree to which a soil can adsorb and exchange anions
**Anion Exchange Capacity**
142
It increases as soil pH decreases
**Anion Exchange Capacity**
143
Common soil anions
- **Chlorine**
- **Nitrate**
- **Sulfate**
- **Phosphate**
144
It is the proportion of acids and bases in the CEC
**Base saturation (%BS)**
145
Soil's ability to maintain a constant pH level during action on it by an acidifier or alkalescent agent
**Buffering capacity of soils**
146
TRUE OR FALSE
The higher the CEC, the more cations can be supplied and the higher the soil's buffering capacity
**TRUE**
147
The degree by which the exchange sites of colloids are occupied by sodium ions
**Exchangeable Sodium Percentage**
148
It is the single most important chemical property of the soil
**Soil pH**
149
pH formula
**pH = -log [H+]**
**pH = log 1/[H+]**
150
What is the most favorable soil pH for most agricultural crops?
**6.0 - 7.0**
151
What is the optimum soil pH?
**6.5**
152
Elements that may become unavailable to plants under acidic conditions
**P, N, Ca, Mg, S, Mo, B**
153
Elements that are unavailable at alkaline conditions
**Fe, Mn, Br, Cu, Zn**
154
TRUE OR FALSE
Activity of bacteria is hindered in strong acid soils
**TRUE**
155
Cations that are responsible for soil acidity
**Hydrogen and Aluminum**
156
Sources of acidity in soil
- **Nitrification**
- **OM decomposition**
- **Root respiration**
- **Acid rain**
- **Uptake of base cations by plants**
- **Leaching of base cations**
157
hydrogen ion concentration in soil water or moisture; these hydrogen ions are in solution
**Active acidity**
158
hydrogen ions attached to clay or organic matter in the soil particles and not dissolved in solution
**Reserve acidity**
159
The ability of soil to resist change in pH
**Buffering Capacity of Soils**
160
TRUE OR FALSE
The greater the buffering capacity of an acid soil, the -lesser- the amount of lime needed to neutralize the acidity
**FALSE**
greater
161
Acidic soils are easily reclaimed by :
**Adding lime**
162
any material containing Ca and/or Mg which when added to the soil can neutralize acidity
**Lime**
163
TRUE OR FALSE
Gypsum is not a liming material
**TRUE**
164
The lime’s strength/effectiveness in correcting soil acidity compared to calcium carbonate
**Relative Neutralizing Value**
165
Soils wherein its soluble salt content is too high and plant growth is adversely affected
**Saline soils**
166
Soil with exchangeable sodium percentage of >15%, highly dispersed and poorly drained
**Sodic soils**
167
The range of soil organic matter (SOM) content of agricultural topsoil
**1% - 6%**
168
Soil organic matter is
**Labile and Renewable**
169
Organic components of a soil
- **Fresh residues**
- **Decomposing OM**
- **Stable OM**
- **Living Organisms**
170
Composition of plant residues wherein it is an amorphous polymer related to cellulose that provides rigidity and together with cellulose, forms the woody cell walls of plants and the cementing material between them
**Lignin**
171
Plant material that is transformed from one organic compound to another mainly by organisms in the soil
**Decomposing Organic Matter (Active Fraction)**
172
TRUE OR FALSE
The active fraction of OM is the most susceptible to soil management practices
**TRUE**
173
What is the stable organic compound?
**Humus**
174
Factors affecting accumulation of OM
- **Climate**
- **Type of vegetation**
- **Soil texture**
- **Tillage**
- **Farming systems**
175
Factors controlling rates of organic matter decay
- **Properties of the organic matter**
- **Amount of organic matter and stage of decay**
- **pH, salinity and mineral nutrients**
- **Water**
- **Temperature**
- **Oxygen**
- **Carbon-nitrogen ratio**
