Chapter 11 Soil. 1. In productive soil, detritus feeders and decomposers constitute a biotic...
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Chapter 11 Soil. 1. In productive soil, detritus feeders and decomposers constitute a biotic community –Facilitating the transfer of nutrients –Creating
1. In productive soil, detritus feeders and decomposers
constitute a biotic community Facilitating the transfer of
nutrients Creating a soil environment favorable to root growth 2.
Productive topsoil involves dynamic interactions among organisms,
detritus, and mineral particles of the soil
Slide 3
Soil formation
Slide 4
Soil characteristics Most soils are hundreds of years old They
change very slowly Soil texture: relative proportions of each soil
type Parent material: mineral material of the soil Soil has its
origin in the geological history of an area Weathering: gradual
physical and chemical breakdown of parent material It may be
impossible to tell what the parent material was
Slide 5
Classification of soil Soil separates: small fragments smaller
than stones Sand: particles from 2.0 to 0.063 mm Silt: particles
range from 0.063 to 0.004 mm Clay: anything finer than 0.004 mm
Clay particles become suspended in water Clay is gooey because
particles slide around each other on a film of water
Slide 6
Soil makeup
Slide 7
Proportions Sand, silt, and clay constitute the mineral part of
soil If one type of particle predominates, the soil is sandy,
silty, or clayey Loam: a soil with 40% sand, 40% silt, and 20%
clay
Slide 8
Soil Texture To determine a soils texture: Add soil and water
to a test tube and let the soil settle Sand particles settle first,
then silt, then clay Scientists classify soil texture with a
triangle It shows relative proportions of sand, silt, and clay
Slide 9
The soil texture triangle
Slide 10
Properties Soil properties are influenced by its texture Larger
particles have larger spaces separating them Small particles have
more surface area relative to their volume Nutrient ions and water
molecules cling to surfaces These properties profoundly affect soil
fertility Infiltration, nutrient- and water-holding capacity,
aeration
Slide 11
Workability the ease with which soil can be cultivated Clay
soils are hard to work with: too sticky or too hard Sandy soils are
easy to work with
Slide 12
Soil profiles Horizons: horizontal layers of soil from soil
formation Can be quite distinct Soil profile: a vertical slice
through the soil horizons Reveals the interacting factors in soil
formation
Slide 13
Soil profiles O horizon: topmost layer of soil Dead organic
matter (detritus) deposited by plants High in organic content
Primary source of energy for the soil community Humus: decomposed
dark material at the bottom of the O horizon
Slide 14
Subsurface layers A horizon (topsoil): below the O horizon A
mixture of mineral soil and humus Permeated by fine roots Usually
dark May be shallow or thick Vital to plant growth Grows an inch or
two every hundred years
Slide 15
Soil profile
Slide 16
Mineral nutrients Initially become available through rock
weathering Phosphate, potassium, calcium, etc. Much too slow to
support normal plant growth Breakdown and release (recycling) of
detritus provides most nutrients Leaching: nutrients are washed
from the soil by water
Slide 17
Fertilizer Agriculture removes nutrients from the soil
Fertilizer: nutrients added to replace those that are lost Organic
fertilizer: plant or animal wastes or both Manure, compost (rotted
organic material) Leguminous fallow crops (alfalfa, clover) Food
crops (lentils, peas) Inorganic fertilizer: chemical formulations
of nutrients Lacks organic matter Much more prone to leaching
Slide 18
Water is crucial for plants Transpiration: water is absorbed by
roots and exits as water vapor through pores (stomata; singular =
stoma) in the leaves Oxygen enters, and carbon dioxide exits,
through stomata Loss of water through stomata can be dramatic
Slide 19
Water is crucial for plants Wilting: a plants response to lack
of water Conserves water Shuts off photosynthesis by closing
stomata Severe or prolonged wilting can kill plants
Slide 20
Transpiration
Slide 21
Water and water-holding capacity Water is resupplied to the
soil by rainfall or irrigation Infiltration: water soaks into the
soil Water runoff is useless to plants and may cause erosion
Water-holding capacity: soils ability to hold water after it
infiltrates
Slide 22
Water and water-holding capacity Poor holding capacity: water
percolates below root level Plants must depend on rains or
irrigation Sandy soils Evaporative water loss depletes soil of
water The O horizon reduces water loss by covering the soil
Slide 23
Plant-soil-water relationship
Slide 24
Aeration Novice gardeners kill plants by overwatering
(drowning) Roots must breathe to obtain oxygen for energy Land
plants depend on loose, porous soil Soil aeration: allows diffusion
of oxygen into, and carbon dioxide out of, the soil Overwatering
fills air spaces
Slide 25
Compaction packing of the soil Due to excessive foot or
vehicular traffic Reduces infiltration and runoff Strongly
influenced by soil texture
Slide 26
Relative acidity (pH) pH refers to the acidity or alkalinity of
any solution The pH scale runs from 1 to 14 7 is neutral (neither
acidic or alkaline) Different plants are adapted to different pH
ranges Most do best with a pH near neutral Many plants do better
with acidic or alkaline soils Blueberries do best in acidic
soils
Slide 27
Salt and water uptake Buildup of salt in the soil makes it
impossible for roots to take in water High enough salt levels can
draw water out of a plant By osmosis Dehydrates and kills
plants
Slide 28
Salt and water uptake Only specially adapted plants grow in
saline soils None of them are crops Irrigation can lead to salt
buildup in soil (salinization)
Slide 29
The soil community To support plants, soils must Have nutrients
and good nutrient-holding capacity Allow infiltration and have good
water-holding capacity Resist evaporative water loss Have a porous
structure that allows aeration Have a near-neutral pH Have low salt
content According to the principle of limiting factors, the poorest
attribute is the limiting factor
Slide 30
Limiting factors in plant growth Sandy soils dry out too
quickly to be good for agriculture They have poor water-holding
capacity Clay soils do not allow infiltration or aeration The best
soils are silts and loams They moderate limiting factors
Slide 31
Limiting factors in plant growth Soil texture limitations are
improved by the organic parts of the soil ecosystem Detritus Soil
organisms
Slide 32
Organisms and organic matter in the soil Dead leaves, roots,
other detritus on and in the soil Support a complex food web
Bacteria, fungi, mites, insects, millipedes, spiders, earthworms,
snails, slugs, moles, etc. Millions of bacteria are in a gram of
soil
Slide 33
Organisms and organic matter in the soil Humus: residue of
partly decomposed organic matter In high concentrations at the
bottom of the O layer Extraordinary capacity for holding water and
nutrients Composting: fosters decay of organic wastes Is
essentially humus
Slide 34
Soil as a detritus-based ecosystem
Slide 35
Soil bacteria
Slide 36
Soil structure and topsoil Animals feeding on detritus also
ingest mineral soil particles Castings: earthworm excrement of
stable clumps of glued inorganic particles plus humus Burrowing of
animals keeps clumps loose
Slide 37
Soil structure and topsoil Soil structure: refers to the
arrangement of soil particles Soil texture: refers to the size of
soil particles A loose soil structure: best for infiltration,
aeration, and workability Topsoil: clumpy, loose, humus-rich soil
Loss of topsoil reduces crop yield by 8590%
Slide 38
Humus and the development of soil structure
Slide 39
The results of removing topsoil
Slide 40
Interactions between plants and soil biota Mycorrhizae: a
symbiotic relationship between the roots of some plants and certain
fungi Fungi draw nourishment from the roots Fungi penetrate the
detritus, absorb nutrients, and pass them to the plant Nutrients
are not lost to leaching
Slide 41
Soil enrichment Most detritus comes from green plants So green
plants support soil organisms Soil organisms create the chemical
and physical soil environment beneficial to plants Green plants
further protect the soil by reducing erosion and evaporative water
loss So keep an organic mulch around garden vegetables
Slide 42
Mineralization If detritus is lost, soil organisms starve Soil
will no longer be kept loose and nutrient- rich Humus decomposes,
breaking down the clumpy aggregate structure of glued soil
particles Water- and nutrient-holding capacities, infiltration, and
aeration decline
Slide 43
Mineralization Mineralization: loss of humus and collapse of
topsoil All that remains are the minerals (sand, silt, clay)
Topsoil results from balancing detritus and humus additions and
breakdown
Slide 44
The importance of humus to topsoil
Slide 45
Erosion Erosion: the process of soil and humus particles being
picked up and carried away by water and wind Occurs any time soil
is bared and exposed Soil removal may be slow and gradual (e.g., by
wind) or dramatic (e.g., gullies formed by a single storm)
Slide 46
Erosion Vegetative cover prevents erosion from water Reducing
the energy of raindrops Allowing slow infiltration Grass is
excellent for erosion control Vegetation also slows wind
velocity
Slide 47
Erosion
Slide 48
Desert Another devastating feature of wind and water erosion:
differential removal of soil particles Lighter humus and clay are
the first to be carried away Rocks, stones, coarse sand remain The
remaining soil becomes coarser Deserts are sandy because wind
removes fine material
Slide 49
Desert pavement Desert pavement: occurs in some deserts Removal
of fine material leaves a thin surface layer of stones and gravel
This protective layer is easily damaged (e.g., by vehicles)
Slide 50
Formation of desert pavement
Slide 51
Drylands and desertification Clay and humus are the most
important parts of soil For nutrient- and water-holding capacity
Their removal results in nutrients being removed Regions with
sparse rainfall or long dry seasons support grasses, scrub trees,
and crops only if soils have good water- and nutrient-holding
capacity Erosion causes these areas to become deserts
Slide 52
Desertification Desertification: a permanent reduction in the
productivity of arid, semiarid, and seasonally dry areas (drylands)
Does not mean advancing deserts
Slide 53
Desertification
Slide 54
Causes of erosion: overcultivation Plowing to grow crops
exposes soil to wind and water erosion Soil remains bare before
planting and after harvest Plowing causes splash erosion Destroying
soils aggregate structure Decreasing aeration and infiltration
Slide 55
Causes of erosion: overcultivation Tractors compact soil
Reducing aeration and infiltration Increasing evaporative water
loss and humus oxidation Rotating cash crops with hay and clover is
sustainable
Slide 56
Apparatus for no-till planting
Slide 57
No-till planting No-till agriculture: a technique allowing
continuous cropping while minimizing erosion Routinely practiced in
the U.S. After spraying a field with herbicide to kill weeds A
planting apparatus cuts a furrow through the mulch Drops seeds and
fertilizer Closes the furrow
Slide 58
No-till planting The waste from the previous crop becomes
detritus So the soil is never exposed Low-till farming uses one
pass (not 612) over a field
Slide 59
Reducing soil erosion Contour strip cropping: plowing and
cultivating at right angles to contour slopes Shelterbelts:
protective belts of trees and shrubs planted along plowed
fields
Slide 60
Reducing soil erosion The U.S. Natural Resource Conservation
Service (NRCS) Established in response to the Dust Bowl Regional
offices provide information to farmers and others regarding soil
and water conservation practices U.S. soil erosion has decreased
through conservation Windbreaks, grassed waterways, vegetation to
filter runoff
Slide 61
Contour farming
Slide 62
Shelterbelts
Slide 63
Irrigation Irrigation: supplying water to croplands
artificially Dramatically increases production Is a major
contributor to land degradation Flood irrigation: river water flows
into canals to flood fields Center-pivot irrigation: water is
pumped from a well into a giant pivoting sprinkler
Slide 64
Flood irrigation
Slide 65
The process of soil formation creates a vertical gradient of
layers that are known as a.loam. b.aeration. c.infiltration.
d.horizons. Review Question-1
Slide 66
The process of soil formation creates a vertical gradient of
layers that are known as a.loam. b.aeration. c.infiltration.
d.horizons. Review Question-1
Slide 67
The residue of partly decomposed organic matter is called
______ and is found in high concentrations at the bottom of the O
horizon. a.desertification b.decomposition c.humus d.topsoil Review
Question-2
Slide 68
The residue of partly decomposed organic matter is called
______ and is found in high concentrations at the bottom of the O
horizon. a.desertification b.decomposition c.humus d.topsoil Review
Question-2 Answer
Slide 69
Mineralized soils can be revitalized through the addition of
a.compost and other organic matter. b.materials from the C horizon.
c.topsoil. d.all of the above. Review Question-3
Slide 70
Mineralized soils can be revitalized through the addition of
a.compost and other organic matter. b.materials from the C horizon.
c.topsoil. d.all of the above. Review Question-3 Answer
Slide 71
______ occurs when there is an accumulation of salts in soil as
a result of ______. a.The tragedy of the commons; overgrazing
b.Deforestation; logging c.Salinization; irrigation
d.Overcultivation; no-till farming Review Question-5
Slide 72
______ occurs when there is an accumulation of salts in soil as
a result of ______. a.The tragedy of the commons; overgrazing
b.Deforestation; logging c.Salinization; irrigation
d.Overcultivation; no-till farming Review Question-5 Answer