Unit 5- Soil Resources Flashcards
Soil Profile:
• Collection of various layers of soil, from surface to bedrock
Each layer is known as a horizon- O,A,B,C, and R
Leaching:
• Process through which minerals are carried downward through the developing soil profile
• Materials suspended or dissolved in liquid are transported through the subsurface
• Acts like a coffee filter- water infiltrates soil, dissolves substances, and carries them down
Some of this material is deposited in zones of accumulation
Soluble Minerals:
• Minerals that are easily leached
• i.e. iron, aluminum, silicate minerals
• In some soils, minerals are leached so quickly that plants are deprived of nutrients
Minerals may be carried into ground water, affecting water quality
O Horizon:
Peat deposits
Litter:
• Surface deposits of leaves, branches, mosses, and animal waste
Form organic horizon in upland forests
A Horizon:
• Uppermost mineral horizon
• Organic mineral components with organic matter and humus from above mixed in
• Often referred to as topsoil
• Rich in nutrients, vital for ecosystems and agriculture
Humus gives topsoil its loose texture and dark colour
B Horizon:
• Subsoil
• Minerals and organic matter leached down from topsoil
• Form hard, mineral rich layers called hardpan, claypan, duripan, or caliche (depending on composition and structure)
Create problems for plants because they interfere with drainage and prevent plant roots from penetrating to lower, nutrient rich horizons
C Horizion:
• Transition zone below B horizon
• Broken up parents material only slightly altered by processes of soil formation
Contains rock particles larger and less weathered than above layers
R Horizon:
• Unaltered parent material
R (rock) horizon
W Horizon:
Some soils have a layer of water
Permafrost:
Some arctic soils contain a perennially frozen layer
Soil Variation:
• Young soils then to be thin
• Not all horizons are present in all soils
Soils classified into various categories using properties such as colour, texture, and pH
Soil Colour:
• Colour can indicate composition and fertility
• Black or dark brown soils usually rich in organic matter
Pale grey to white soils usually chalky, leaching, or are low in organic content
Loam:
Soil with a relatively even mixture of clay, silt, and sand
Regional Differences and Soil Productivity:
• Rainforest ecosystems have high primary productivity, but nutrients are trapped in plants, not in the soil
• Temperate grasslands (prairies) have much higher productivity in soil
• High volume of rain in rainforests leaches minerals and nutrients out of topsoil- those not captured by plants are taken down to the water table
High temperatures speed decomposition of leaf litter and uptake of nutrients by plants, so only small amounts of humus are present, and layer of topsoil remains thin
Swidden Agriculture:
• In tropical rainforests, organic matter is in the plant biomass, when plants are cleared, the soil’s fertility is depleted
• Farmers cultivates a plot for a few years, clears it, and then moves onto a new plot, leaving the first one to grow back to forest
Works for low population densities, but soils are not given enough time to regenerate in today’s population
Plant Fertility in Temperate Grasslands:
• Rainfall low enough to prevent leaching of nutrients
• Plants take up nutrients and return them to soil when they die
• Low temperatures slow rate of decomposition, organic matter mainly stored below ground
Topsoil in grasslands can be farmed repeatedly with minimal loss of fertility if properly kept
Human Acceleration of Erosion:
• Over cultivating fields through poor planning or excessive ploughing, especially when land is left bare (no vegetative cover)
• Over grazing rangelands with more livestock than the land can support reduces vegetative cover
Clearing forested areas on steep slopes or with large clear cuts
Mechanisms of Erosion:
• Several types of erosion can occur, including wind erosion and 4 principal kinds of water erosion
• Rill erosion has the most potential to move topsoil, followed by sheet erosion and splash erosion
• All types of water erosion, particularly gull erosion, are more likely to occur where slopes are steeper
• Steeper slopes, greater precipitation, and sparser vegetative cover leads to greater water erosion
• Vegetation breaks up wind, slows water, plant roots hold soil in place and take up water
Removing plant cover accelerates erosion
Universal Soil Loss Equation (USLE):
• Tool for estimating erosion losses by water from cultivated fields to show how different soil and management factors influence soil erosion
The Dust Bowl:
- Native prairie grasses in grasslands used to hold erosion prone soils in place
- People moved to grasslands, cultivated wheat, ranchers grazed cattle, caused erosion by removing native grasses and breaking down soil structure
- Drought, strong winds intensified these effects, creating dust storms, grasshopper infestations
Erosion Control:
• Stabilize eroding banks along creeks and roadsides by planting plants to anchor soil
Plant plants in rows to protect open fields from wind
Crop rotation
○ Alternating kind of crop grown in a particular field from season to season
○ Returns nutrients to the soil, breaks cycles of disease associated with continuous cropping, minimizes erosion that occurs from letting fields lie exposed
○ i.e. rotating between what and legumes- legumes have nitrogen fixing bacteria in roots, can revitalize soil
If an insect lays effs on one particular crop, planting a different crop will leave its offspring with nothing to eat
Intercropping
○ Planting different types of crops in alternating band or other spatially mixed arrangements
○ Slows erosion by providing more ground cover than a single crop does
Reduces vulnerability to insect and disease, replenishes soil when a nitrogen fixing legume is one of the crops
