3.4 the soil system. the soil system soil is a complex mixture of eroded rock, mineral nutrients,...
TRANSCRIPT
3.4 The Soil System
The Soil SystemSoil is a complex mixture of eroded rock,
mineral nutrients, decaying organic matter, water, air and billions of living
organisms (microscopic decomposers).
Soil formation is a slow process:
1. Weathering of rock (mechanical).
2. Deposition of sediments by erosion (mechanical).
3. Decomposition of organic matter in dead organisms (chemical).
soil system integrates the biotic and abiotic
Mature soils are arranged in a series of zones called SOIL HORIZONS:
“O” HORIZON = freshly fallen and partially decomposed leaves, twigs, animal waste. You can find fungi and other organic materials.
“A” HORIZON = porous mixture of partially decomposed organic matter (humus) and some inorganic mineral particles.
These top two layers are most fertile, have the highest concentration of organic
matter, and contain large amounts of living organisms.
Flatworm
Rove beetle
AntCentipede
Mite
Pseudoscorpion
Groundbeetle
Adultfly
Millipede
Flylarvae
Sowbug
Mite
Earthworm
Slug
Snail
Roundworms
Protozoa
Bacteria
Organic debris
Beetle Mite
Fungi
Springtail
Actinomycetes
“B” (subsoil) and “C” (parent material) HORIZON contain most of the soil’s
inorganic matter, broken-down rock.
Soil Content
• Clay (very fine particles)• Silt (fine particles)• Sand (medium-size particles)• Gravel (coarse to very coarse particles) SOIL TEXTURE is determined by the relative amounts
of the different types and sizes of mineral particles.
100%clay
Increasingpercentage silt
Increasingpercentage clay
0
20
40
60
80
80
60
40
20
0
100%sand 80 60 40 20 100%silt
Increasing percentage sand
sandyclay
clay
siltyclay
silty clayloam
clayloam
loam siltyloam
silt
sandy clayloam
sandyloam
loamy sandsand
• Soil texture helps determine SOIL POROSITY, a measure of the volume of spores or spaces per volume of soil and the average space between those spaces.
• INFILTRATION is the downward movement of water through soils.
• As the water seeps down, it dissolves various soil components in upper layers and carries them down to lower layers in a process called LEACHING.
SOIL PERMEABILITY is the rate at which water and air move from upper to lower soil layers.
Water Water
High permeability Low permeability
Properties of Soils with Different Textures
Texture Nutrient Capacity
Infiltration Water-Holding Capacity
Aeration Workability
Clay Good Poor Good Poor Poor
Silt Medium Medium Medium Medium Medium
Sand Poor Good Poor Good Good
Loam Medium Medium Medium Medium medium
Nitrogen fixingby lightning
Commercialinorganicfertilizer
10-6-4N-P-K
Organic fertilizers,animal manure,
green manure, compost
Cropplant
Deadorganic matter
Applicationto land
Nitrogen fixingby bacteria
Nitrogen fixing
Weatheringof rock
Nutrient removalwith harvest
Decomposition
Supply ofavailable plant
nutrients in soilNutrient lossby bacterialprocesses
such asconversion
of nitrates tonitrogen gas
Nutrient lossfrom soil erosion
Absorption of nutrientsby roots
Pathway of plant
nutrients in soil.
Soil erosion is the movement of soil components, especially surface litter and topsoil.
• The two main agents of erosion are wind and flowing water.
• Loss of plant cover by farming, logging, construction, overgrazing by livestock, off-road vehicles, deliberate burning of vegetation and other activities leave soil vulnerable to erosion.
Two major harmful effects of soil erosion:
1. Loss of soil fertility and its ability to hold water
2. Runoff of sediment that pollutes water, kills fish and shellfish, and clog irrigation ditches, boat channels, reservoirs, and lakes.
serious concern
some concern
Stable areas
Desertification is the enlargement of deserts through human
activities.
ConsequencesCauses
Worsening drought
Famine
Economic losses
Lower living standards
Environmentalrefugees
Overgrazing
Deforestation
Surface mining
Erosion
Salinization
Soil compaction
SALINATION
1. Irrigation water contains small amounts of dissolved salts.
2. Evaporation and transpiration leave salts behind.
3. Salt builds up in soil.
WATERLOGGING
• Precipitation and irrigation water percolate downward.
• Water table rises.
Both result in stunted plant growth,
lower crop yields,
dead plants and ruined land.
Evaporation
EvaporationTranspiration
Evaporation
Waterlogging
Less permeableclay layer
Soil Conservation involves reducing soil erosion and restoring soil
fertility.
Advantages Disadvantages
Reduces erosion
Saves fuel
Cuts costs
Holds more soil water
Reduces soil compaction
Allows several crops per season
Does not reduce crop yields
Can increase herbicide use for some crops
Leaves stalks that canharbor crop pests and fungal diseases and increase pesticide use
Requires investment in expensive equipment
Advantages and disadvantages of using Conservation Tillage.
Contour planting and strip cropping: each row acts as a small dam to help hold soil and slow water
runoff.
Alley cropping or agroforestry: several crops are planted together in strips or alleys between trees and shrubs that can
provide fruit or fuel-wood, shade, help retain and slowly release soil moisture, and fodder for livestock.
Windbreaks or shelterbelts of trees reduce wind erosion, help retain soil, supply wood for fuel, and provide habitats for birds,
pest-eating and pollinating insects, and other animals.
Terracing retains water for crops at each level
and reduces soil erosion
by controlling runoff.
Soil Restoration
• Organic fertilizer
• Manure
• Compost crop rotation
• No till farming
• Contour farming
• Terracing
• Nitrogen fixation-legumes