Soil final Flashcards
Soils differ from parent material in many ______,_______, and _______ properties.
Physical, chemical, biological
Term given to the top layer of soil that is strongly affected by the roots of vegetation is
The rhizosphere
What three particle types (from smallest to largest) are used to determine soil texture?
Clay, silt, sand
Why are loamy soils generally considered best for plant growth?
Loamy soils hold water but also drain well so roots are aerated.
Between sand and clay, which has less total pore space? Describe why?
Clay has less pore space because the particles are flat, so they stick together easier.
What are the five soil forming factors
Parent material, climate, organisms, time, relief
Define O horizon
Horizon composed mostly of organic matter
Define A horizon
Uppermost horizon, mostly mineral material but still rich in organic material
Define E horizon
Subsurface horizon with some clay, FE and/or Al removed, lighter in color than the A horizon
Define C horizon
Contains geologic materials, little change due to soil formation
What defines a soils mineral content?
Parent rock material, percentage of organic matter, quantity of clay
Define B horizon
Subsurface horizon, contains accumulated clay, FE, or AI, with a difference in color and soil structure
Define rock layer
Hard bedrock
What are the three main soil types in the coastal PNW and their subcategorires
Glacial - till, outwash, lacustrine
Tephra - mudflow
Flood deposits - Alluvium
Clay particles have a net ________ charge.
Negative
What is a reason that Cation Exchange Capacity(CEC) is an important property of soils?
Cations (postively charged nutrient ions) are attracted to negatively charged surfaces in soils, replenishing nutrients that were used by the plant or leached away.
Atmospheric nitrogen must be fixed or changed to an available form for plants to use. Why is this necessary? Why cant plants directly use atmospheric nitrogen?
Plants absorb N2, not gaseous nitrogen. Plants require nitrogen fixing bacteria to make nitrogen available for root uptake.
Besides fertilization, what human activity has impacted the amount of nitrogen in soils?
Tilling
What are exudates and what function do they perform in soils?
Exudates are sticky substances that plants secrete made of organic compounds like sugars or acids that increase nutrient availability in soil.
Define humus
Brown to black active component of soil organic matter that is largely responsible for water retention, nutrient absorption, aggregate stability, and pesticide sorption.
What is the difference between soil erosion and mass wasting of soils?
Soil erosion happens gradually over time, caused by chemical or mechanical weathering. Mass wasting is a rapid transformation of topography usually caused by gravity (landslides, rockfalls)
Define soil erosion
The process by which the top layer of soil is removed by natural forces such as wind, water, or human activity, eventually causing degradation of soil structure.
What is the difference between soil porosity and soil permeability?
Soil porosity is the measure of the volume of spaces within the soil that indicates how much air or water the soil can hold.
Soil permeability is the soil’s ability to transmit water or air through its pores, indicating how easily fluids can flow through the soil.
Porosity is associated with the STORAGE of water, permeability is more associated with water MOVEMENT.
Define colluvium
Soil formed by gravity, loose unconsolidated material that accumulates at the base of steep slopes.
Define alluvium
Soil formed from unconsolidated sedimentary material, deposited by water.
Define marine soils
Sediments formed underwater deposited by marine processes like currents, waves, and tides.
Define lacustrine soil
Soil deposited in lakes consisted of fine grained sediments formed through erosion and sedimentation in lake environments.
Define glacial till
Unsorted, heterogenous material formed by, transported, and deposited by glaciers.
Define glacial outwash
Sediment deposited by meltwater streams from glaciers, usually well-sorted.
Define glacial lacustrine soil
Sediment deposited in glacial lakes, often stratified.
What are the three main factors that determine a soils mineral content?
Parent material, climate, and time
What does Cation Exchange Capacity and why is it important in soil?
Refers to a soil’s ability to retain and exchange positively charged ions (cations) such as calcium, magnesium, and potassium. It influences nutrient availability and soil fertility.
Define buffering capacity and explain why it is important in soils
The ability to resist changes in pH, which helps to maintain stable pH levels to optimize nutrient availability to plants.
How can a soils buffering capacity be increased?
By adding materials like lime or organic matter, which helps neutralize acids.
Define diffusion and explain how it assists in plants ability to uptake nutrients from surround soil
Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
Diffusion assist in nutrient uptake from surrounding soil by allowing nutrients to move from regions of higher concentration in soil to regions of lower concentration in the plant roots.
Describe the soil food web and why it is important in soil development
The soil food web describes the interactions between soil organisms like bacteria, fungi, protozoa, and nematodes. These decompose organic matter and recycle nutrients in the soil which enhances soil structure and fertility.
What are soil microfauna and why are they important in soil development
Soil microfauna are small soil organisms like bacteria, fungi, and protozoa. They are important because they DECOMPOSE organic matter, release nutrients, and help control populations of other soil organisms.
What are soil macrofauna and why are they important in soil development
Soil macrofauna are larger soil organisms such as worms, beetles, and ants. They improve soil structure through BURROWING which enhances aeration and drainage, facilitating nutrient cycling.
Why would a large population of soil macrofauna be a good indicator that you have a very healthy, nutrient rich soil with lots of available soil nutrients?
A large population of soil macrofauna indicates a healthy nutrient rich soil with ample organic matter and available nutrients because these organisms thrive in such conditions and contribute to soil fertility through their activites.
Explain the symbiotic relationship between mycorrhizae and roots
Mycorrhizae provide the roots with water and nutrients such as phosphorus and nitrogen, while the roots provide the mycorrhizae with sugars through photosynthesis.
What is denitrifying bacteria and where is it typically found? Why is it important in the nitrogen cycle and what is it doing to nitrogen compounds it encounters?
Denitrifying bacteria are microorganisms that convert nitrate and nitrite back into nitrogen gas or nitrous oxide; usually found in waterlogged or poorly aerated soils. They are important because they reduce soil nitrogen levels, which prevents excess nitrogen from accumulating in ecosystems.
What are two high energy natural events that can break N2 bonds and make nitrogen available for plants in soil
Lightning strikes and wildfires
Why is too much nitrogen in soil bad?
It can lead to eutrophication, air and water pollution, loss of biodiversity, and soil degradation.
Describe the nitrogen cycle
Nitrogen fixation - bacteria convert atmospheric nitrogen into ammonia or nitrate which plants use for growth
Assimilation - plants absorb nitrogen form the soil and use it to build proteins, DNA, and other essential molecules
Ammonification - After plants die, decomposers like bacteria and fungi break down the organic matter, releasing ammonia
Nitrification - Ammonia is converted into nitrite and then into nitrate by nitrifying bacteria in the soil
Assimilation (again) - plants absorb nitrate from the soil through their roots and use it to build proteins
Denitrification - Bacteria in waterlogged or oxygen-depleted soil convert nitrate back into nitrogen gas or nitrous oxide and release it into the atmosphere
How many mineral nutrient elements are needed for plant growth?
13
How do plants take up mineral elements from the soil?
Bulk flow - uptake in the transpiration stream; diffusion
Mycorrhizae - carbon-nitrogen exchange with roots
What are two sources of nitrogen for plants?
Fixation of atmospheric nitrogen by bacteria
Decomposition of organic matter
What are the elements of the morphology of soil horizons
Color, structure, texture, coarse fragment content, humidity, and consistence
What are four types of physical weathering
Thermal stress
Wetting and drying
Freezing and thawing
Abrasion
What are four types of chemical weathering
Oxidation
Hydrolysis
Carbonation
Concretions
What does microbial refer to
Microorganisms such as bacteria, fungi, and protozoa; microbial biomass decreases with depth
How much bacteria is in one teaspoon of soil
100 million to 1 billion
Define slopewash
AKA sheet erosion - earth material transported by rain
