Kaitlin Scott
Chapter 14 Outline: Soil Resources
 Many dust storms occur here from the expanding Gobi Desert
 The storms damage crops, grounds, air traffic, and cause other
 The Three-North Shelterbelt was formed to protect China from the dust
 It reduces the frequency and severity of the storms
 It is a wall of millions of trees that slow the wind’s force
 The trees also provide a moist forest floor that prohibits more loose dust to
join the storm
 Humans help cause the dust storms by the removal of forests, over collection
of firewood, and overgrazing by sheep and goats on semiarid steppes
(shortages prairies) which caused the soil to loosen and make it easier to
become part of the dust storms
 Desertification is a big problem in China
 Desertification-the progressive degradation of grassland and other
productive lands into unproductive desert
 Planting trees can improve soil quality
 China has started grassland restoration projects in some areas of northern
China and Mongolia, these areas are too dry to grow trees
Soil-the uppermost layer of Earth’s crust, which supports terrestrial plants, animals,
and microorganisms
-filled with minerals and organic matter
-natural actions like weather, wind, water, and organisms modify it
-supports almost all terrestrial food webs
-microorganisms inhabit it and depend on it for shelter, food, and water
-plants attach themselves in soil where they receive important nutrients
-humans cannot exist without soil because we depend on plants for dood and
the plants depend on soil and we eat
State Factors: Soil Forming Factors
 State factors-determine the state of the soil system
 Main factors: parent material, climate, topography, organisms, and time
 Parent material-rock that is slowly broken down into smaller pieces by
biological, chemical, and physical weathering processes in nature
 Parent material forms soil
 A lot of time is needed for the rock to disintegrate into soil, and time is
needed for organic material to form in soil
 Forming soil is a process of interactions between Earth’s solid crust and the
The process of weathering parent material under already formed soil help
adds new soil
Thin layers of soil dorms on young lands, thick layers form on old lands
Carbon dioxide is formed when plant roots and other organisms in the soil
The carbon dioxide goes into the soil and reacts with the water in the soil to
from carbonic acid
The acid and water goes into the cracks of rocks
If there is temperate weather when the parent material is in the rock,
freezing and thawing of water during the winter will cause the cracks to get
bigger and the rock breaks
Small plants form in the cracks and their roots cause the rock to break evern
Topography affects formation of soil
Steep slopes don’t have soil because gravity and precipitation causes it to fall
Moderate slopes help soil form
Humans are state factors because they influence environmental processes
like carbon and nitrogen cycles
They effect soil formation by agriculture, urbanization, mining, pollution,
deforestation, and forestation
Soil Composition
 Four layers: mineral particles, organic matter, water, air
 Soil has layers
 The organisms that live in soil interact with it (plants, animals, fungi, and
 Nutrients are always cycled in soil because when organisms die they are then
broken down
 Minerals makes of most up of soil
 Comes from weathered rocks
 Provides nutrients needed for plants and has pores where water and air is
 Various types of rocks provide various types of nutrients in soil
 Soils from the same parent material may be different because of weather,
topography, and organisms
 Soil age affects its mineral composition
 Older soils have lower amounts of nutrients and are weathered
 New soils have more nutrients and can be found in geologically young soils
and in areas formed by volcanic activity
 Soil organic matter-natural litter, animal poop, dead plants, animals, and
microorganisms that are being decomposed
 The decomposition of this adds nutrients to the soil and increases the
amount of water the soil can hold
Humus-dark colored organic material that is left after decomposition
Is a combination of many organic compounds and holds water
Last in soil for many years and is broken down by earthworms, termites, and
Pores in soil hold water to makes a moist but aerated soil
Provides great habitat for plants and other organisms
Water held in smaller pores, air held in bigger pores
Soil water is either provided by precipitation which drains down, or
groundwater which moves up
Water has low concentrations of dissolved nutrient mineral salt
Soil air has same gases as atmospheric air
Contains a little more carbon dioxide then oxygen because of cellular
Important gases in soil include oxygen (used for cellular respiration),
nitrogen (used by nitrogen-fixing bacteria), and carbon dioxide (used in soil
Soil Horizons
 Deep cuts through many soils
 Soil profile-a vertical section from surface to parent material
 Top layer of soil (O-Horizon) has a lot of organic material
 A-Horizon is next layer, has a lot of organic matter and humus, nutrient poor
 E-Horizon, which is heavly leached, sometimes forms between the A and BHorizons
 B-Horizon, beneath A-Horizon, nutrient minerals that have leached from
previous horizons form here
 C Horizon has weathered pieces of rock
Soil Organisms
 Many mircoorganims in soil
 Bacteria most common in soil
 Organisms provide important ecosystem services (marinating soil fertility,
preventing soil erosion, breaking down toxic pollutants, cleansing water,
affecting the composition on the atmosphere
 Worms important
 Ingest soil and get energy by digesting compounds in humus
 Castings (bits of soil that have passed through gut of worm) are left on soil
surface and helps distribute nutrient minerals
 Ants help aerate soil by having tunnels
 Food not eaten by them help add to organic material
 Plant growth either depends on the soil type, or the soil type depends on the
plant and what it provides it
 Mycorrhizae-symbiotic relationship between fungi and roots
 Allows plants to absorb nutrients
Fungi mycelium (thread like body) helps it absorb more nutrients which it
transport to the plant
The plant helps provide food to fungi through photosynthesis
Nutrient Cycling
 Decomposition part of it
 Nutrient cycling is the passage of nutrients from the environment through
organisms and back to the environment
 Bacteria and fungi decompose dead organisms which releases nutrient
minerals that return to the soil and environment
 Weathering of parent material is a abiotic nutrient cycle
Soil Texture
 Soil texture-proportions of different inorganic mineral particles of sand, silt,
and clay
 The size of these particle allow scientists to classify soil texture
 Sand largest particle
 Silt medium sized
 Clay is the smallest
 Soil texture affects soil’s properties
 Clay has greatest surface areas so is most important
 Soil minerals are either in charged forms or ions
 Either positively or negatively charged
 Clay particles have mostly negative charges which attract positively charge
 Positively charged ions are important and stored in plants for interaction
with clay
 Negatively charged ions are usually washed away
 Loam-ideal agricultural soil
 Loam has many different soil particle sizes
 Bigger particle proved structural support, aeration, and permeability to soil
 Smaller particles bind close together and hold nutrient minerals and water
 Soil with a lot of sand is not good because it doesn’t hold mineral ions r water
 Soil with a lot of clay is not desirable because it has poor drainage and not
enough oxygen
Soil Acidity
 Measured using pH scale
 Most soil’s pH range is from 4 to 8
 Soil nutrients are available based on their pH levels
 Plants can absorb soluble elements not insoluble
 pH affects leaching
 acidic soils are not able to hold positive ions as well which results in
important nutrients like potassium are leached from the soil quicker
the prime pH level is 6.0 to 7.0 because that is when most important minerals
are available
decomposition of humus and cellular respiration decreases pH levels
the needles of conifers has acids that power the pH level
acid precipitation-air pollution that has human-produced sulfuric and nitric
acids that enter the ground through acid rain, sleet, snow, or fog
Soil Types
 climate, vegetation, parent material, underlying geology, topography, and soil
age help produce various types of soil
 soil taxonomy-method of classification of the soils into 12 orders, which are
then subdivided into series
 most common orders: spodosols, alfisols, mollisols, and oxisols
 spodosols-distinct layers, located in cold regions with a lot of rain, has OHorizon of acidic litter, leached and acidic E-Horizon, illuvial B-Horizon, not
good for farming because it is too acidic
 alfisols-temperate deciduous forests grow on it, brown to brow-gray AHorizon, precipitation washes clay and soluble minerals into B-Horizon,
fertilized needs to be used to maintain fertility if soil is used for farmland
 mollisols-in temperate and semiarid grasslands, fertile, nutrients remain in
top level, most of world’s grain grows here example of the involvement of
organisms in soil formation
 aridisols-in arid regions, lack of rain prevents leaching, lack of vegetation
limits organic matter, no definite layers of leaching and illuviation, some have
a salty A-Horizon, provide land for grazing animals, crops can be grown with
provided with water by irrigation
 oxisols-low in nutrient minerals, in tropical and sub-tropical areas with a lot
of rain, not a lot of organic matter, A-horizon rich with humus, B-Horizon
highly leached and nutrient poor, nutrient rich vegetation is quickly
decomposed for nutrient minerals
humans need to understand how soil works in order to protect it
Sustainable soil use-wise use of soil resources without a reduction in soil
fertility so that soil remain productive for the future
Soil Erosion
 When water, wind, ice caries away and removes soil, especially top soil
 Rain loosens soil which makes it easier for water to carry it away
 Wind loosens soil and blows it away
 Soil erosion is a natural process, but humans quicken the process
 Soil lessens the amount of nutrients in soil which then causes the need to use
 Humans accelerate soil erosions by having poor soil management
Soil erosion affects other natural resources because sediment gets in
streams, rivers, and lakes which affects water quality
Erosion is a big problem in the United States especially in Iowa, northern
Missouri, western and southern Texas, and eastern Tennessee
Erosion did decrease by 38% between 1982 and 1997

Chapter 14 Scott - Crowley AP Environmental Science