Soil Science Q2 Flashcards
Adhesion
The attraction of water molecules to solid surfaces
Cohesion
The attraction of water molecules to each other
Surface Tension
Greater attraction of water molecules to each other than to the air
What are the six functions water performs in soil?
- Facilitates plant life
- Facilitates for microbial life
- Temperature regulation
- Facilitates soil formation
- Breaks down waste
- Acts as part of water cycle
What is the prime driver of the water cycle?
Solar energy
Interception
Precipitation that doesn’t reach soil (e.g. blocked by plant cover)
Runoff
Precipitation that flows away from the area via stream channels
Can be surface or groundwater
Infiltration
Vs.
Percolation
Downward movement of water into the soil
Vs.
Downward movement of water within the soil
Transpiration
The process of water being absorbed and released by plants without reaching the soil
Watershed
A group of groundwater separated from other groups of groundwater via drainage or dam structures
Riparian Area
The stretcher of land near the shore of a body of water
What four functions does a riparian area with lots of plant cover perform?
- Stabilizes banks and reduces erosion thereof
- Provides food and shelter to a large variety of organisms
- Controls pollution by reducing release of nutrients, waste, and sediment into water
- Increases aesthetic and recreational value of land
Where is the majority of freshwater found (and what percentages)
- 68.7% in glaciers
- 30% in groundwater
- 1.2% usable
What percentage of water usage is used in agriculture
70%
What 3 factors cause water to be scarcer in some areas than others?
- Unequal water distribution
- Unequal population distribution
- Flood irrigation
What are two practices that can increase our available water?
- Desalinization
- Drip irrigation
Aquifer
A body of rock/soil that holds groundwater
Saturated Flow
Movement of water in soil where both micropores and macropores are filled with water
Movement controlled by macropores via gravity
Unsaturated Flow/Capillary Movement
Movement of water in soil where micropores but not macropores are filled with water
Movement is controlled by adhesion and surface tension/cohesion
Vapor Flow
Movement of water in very dry soils
Movement controlled by evaporation
Darcy’s Law
Water moves from areas of low matric potential to high matric potential
Matric Potential/Water Potential
The strength of attraction between a soil particle and its surrounding water
Drier soils have higher Matric potential
Hydraulic conductivity
The ease with which water moves within the soil
Hygroscopic Water
Water that forms a film around soil particles, not available for plant use
Capillary Water
Water within soil micropores, available for plant use
Gravitational Water
Water within soil macropores
Filled Capacity
The optimal point of water saturation for plant growth
The condition in which approx. 1/2 of pore space is filled with water
Wilting Point
The minimal point of water saturation required for plants to survive (w/o wilting)
Permanent Wilting Point
The point of water saturation where plants cannot take water from the soil and will not recover even if water is added
Maximum Capacity
The point where all pore space in the soil is filled with water
The maximum amount of water the soil can hold
What are the two best ways to slow evaporation from the soil?
Increase ground plant cover
Increase plant canopy cover
What does air accomplish within the soil
Allows respiration in microbes and plants
How does air composition within soil compare to atmospheric air?
They are mostly the same
What is the most important factor in determining soil aeration?
What two factors affect that?
Macropore size
Soil Structure and texture
What 3 factors can characterize soil aeration?
- Oxygen content
- Soil oxidation
- Air-filled porosity
Mass Flow
Air moved by root and water movement
What is the primary mode of air movement?
Diffusion
What 3 factors affect oxygen availability in soil?
- Macropore quantity
- Amount of microbial respiration
- Water content
How much faster does oxygen diffuse in pore spaces filled with air versus water?
10X
What color soil does anaerobic oxidation cause?
Gray
Redoximorphic Features
Red and black splotches in soil caused by iron and manganese oxides
Which types of soil change temperature faster?
Bare soils and dry soils
Specific Heat
The amount of energy required to increase 1g of soil by 1 degree
Respiration rates in soil double for every _ increase in temperature
10 degrees (up to 35)
Why do soils in different areas have different respiration rates?
The amount/types of plants present
What are five ecological processes does soil aeration affect?
- Organic matter decomposition
- Oxidation
- Soil Color
- Methane Production
- Activities of higher plants
Ogallala Aquifer
The aquifer that supplies much of the great plains region, supplies 30% of water used in agriculture
Forbes
Shrubbery
Soil Colloids
The smallest particles in a soil, in the form of clay and humus
Solid phase components of cation/anion exchange in soil
Polysillicates
The structure of clay colloids
Forms thin layers of tetrahedrals and octohedrals
1:1 silicate clay
A polysilicate clay consisting of equally alternating layers of tehtrahedral and octahedrals
Not prone to stretch/shrink, and good for agriculture
2:1 silicate clay
A polysilicate clay consisting of layers of octahecrals sandwiched between layers of tetrahedrals
Twice as many tetrahedral layers as octahedral layers
Prone to stretch/shrink, and therefore poor for agriculture/construction
Good for lagoons/ponds
Crystalline Clay Silicate
Silicate clay consisting of 1:1 clay w/ tight bonds of oxygen, silicone, and aluminum
Usually negatively charged
Non-Crystalline Clay Silicate
Silicate Clay consisting of 2:1 clay w/ loose bonds of oxygen, silicone, and aluminum
Usually negatively charged w/ high capacity for cation exhange
Most common colloid in soil
Crystalline clay silicate
Oxides
Colloids in soil consisting of iron oxide, aluminum oxide, oxygen, and hydrogen
Non-expanding, non-plastic, and low cation exchange potential
Can be positive or negative
Most common in old soils (ultisols, oxisols)
2 Major Sources of Charge in Soil
- Hydroxyls/changing pH
- Constant charge/charge by isomorphic substitution
Hydroxyl Group
A molecule consisting of an oxygen atom bound with 2 hydrogen atoms
Isomorphic Substitution
The isotope normally present in the soil has been replaced by a different yet similar isotope, resulting un a continuous charge equivalent to the charge difference between the two isotopes
Humus
Dirt formed from organic matter (must be no longer recognizable as organic matter)
Nonmineral, noncrystaline substance made from chains or rings of carbon
High water/cation absorption potential, not sticky or pliable, but prone to changes in pH
What is the smallest colloid?
Humus
How much more carbon is contained in the soil than in all organic matter on earth?
3X
Carbon offset
A tract of land left undeveloped for purpose of trapping CO2 in soil
What 5 functions does increased soil organic matter improve?
- Water infiltration
- Water retention
- Cation Retention
- Soil structure
- Nutrient cycling
What are the four primary contributors to soil organic matter, in order from most to least contribution
- Grasses
- Forbes
- Trees
- Animals
Lignin
Supportive tissue found in vascular plants
The older the plant, the more lignin is present
3 stages of organic matter decomposition
- Litter
- Duff (feels like OM, but not recognizable)
- Humus
45% of all soil carbon is contained in what 3 soil orders?
Histisols
Inceptisols
Gelisols
What 2 factors influence biomass degredation?
Soil conditions
Quality of added plant residue
What is the maximum carbon to nitrogen ratio in soil to support plant life?
25:1
Vermicomposting
Composting aided by earthworms
Thermophylic Composting
Intense decomposition caused by large, well-aerated piles that generate lots of heat
What 4 functions does organic matter perform in soil?
- Decomposition of organic materials
- Transform organic matter into usable compounds
- Release plant nutrients into soil
- Pollution control
How much matter do earthworms consume in a day?
In a year?
Their body weight each day
10 tons per acre per year
Functional Diversity
Number of biological processes occurring in a sample
What are the three way to measure biological activity in a soil?
- Measure population
- Measure biomass
- Measure Metabolic activity
What type of soil are molds found in?
Acidic soils
Mychorrizae
Fungus roots, often connect to plants
Actinomycetes
Bacteria-like organisms that that have branching roots like fungi
Responsible for dirt smell
Prefers warm, moist, pH-neutral soils
