3.4 The soil System
Structure of a soil
Insoluble rock particles
eg. gravel, sand, clay.
Soluble particles eg.
Nitrates, minerals
Provides a skeleton of
the soil. May come
from the bedrock or be
washed in from
elsewhere.
Soil organisms eg
worms. Break
down the dead
organic matter.
Aerate and drain
the soil. Microorganisms, add
or remove
nutrients eg
nitrates.
Air, mainly N and O2 . Allow
respiration for soil organisms
and plant roots
Water seeps down from rain
or up from underground by
capillary action. Moves
soluble minerals around in
the soil.
Humus. Dead organic
(mostly plant or
animal) matter that is
decaying. This returns
minerals that where
taken originally from
the soil
http://www.dse.vic.gov.au/dpi/vro/vroimages.nsf/Images/soilhealth_soil_structure/$File/soilhealth_soil_structure.gif
• O – Leaf litter and dead
organics.
• A – layer with a mix of
humus from above and
minerals from below with
many living organisms eg
fungi, bacteria, worms…
• E – region where minerals
and organic matter have
been leached leaving silica
behind.
• B - layer where soluble
minerals and organic
matter from above ends
up.
• C – Weathered bed rock,
breaking into smaller and
smaller particles.
• R - Bedrock
http://www.enchantedlearning.com/geology/soil/soillayers.GIF
Soil Processes - Translocation
• The movement of water within the soil - it can
be either up or down.
Water
http://www.enchantedlearning.com/geology/soil/soillayers.GIF
Soil Processes - Salinization
• In dry climates,
where evaporation
is higher than
precipitation, water
moves up the soil
taking dissolved
Water
minerals with it and
depositing them on
the surface.
http://www.enchantedlearning.com/geology/soil/soillayers.GIF
Soil Processes - Leaching
Water
• In wet regions,
where there more
precipitation than
evaporation, the
water moves
down towards the
bedrock taking
dissolved minerals
away from the
surface.
http://www.enchantedlearning.com/geology/soil/soillayers.GIF
Soil Processes - Podsolization
Water
• In very wet regions,
where there lots more
precipitation than
evaporation, and there
is extreme leaching of
the minerals to make
the soil acidic with a
nutrient poor bleached
‘A horizon’ and a very
red ‘B horizon’ full of
Iron oxide
http://www.enchantedlearning.com/geology/soil/soillayers.GIF
Soil Processes - Gleying
• When the water cannot drain away the soil becomes
water logged and the air spaces in the soil fill and so
become poor in oxygen making a very blue/grey soil–
eg a rice paddy. Tends to become nitrate poor due to
nitrifying bacteria needing oxygen to create nitrates.
Microsoft Clip art
Soil Processes - Ferallitization
• Tropical soils
become very red
because of
podsolization
speeded up by high
temperatures.
When clay breaks
down to silica it
gets leached away
leaving Iron and
aluminium oxides
behind.
Microsoft Clip art
Activity
• Make a systems diagram to show the movement of
nutrients coming from water, organic matter and
minerals through the soil system. Show the
transfers and transformations and label the
processes.
Living
biomass
Assimilation
Detritus
/Humus
Soil
Jill Rutherford - Environmental Systems and Societies Course Companion (Page 230)– Oxford University Press
Bedrock
Different types of soil
• Clay particles <0.002mm
diameter
• Silt particles
0.002 – 0.005mm diam.
• Sand particles
0.005mm + diameter
Think
colours!
http://www.atpm.com/9.08/images/design-color_triangle.gif
http://www.sciencebuddies.org/mentoring/project_ideas/EnvSci_img014.jpg
Properties of soil types
Sand
Loam
Clay
Mineral
content
High
Relatively low due to
higher organic content
High
Drainage
High – big particles give
big spaces so water
flows easily
Intermediate
Low – small particles sit
close together leaving
little space for water to
flow
Water
holding
capacity
Air spaces
Low
Intermediate
High
High
Intermediate
Low
Biota –
Amount of
Living stuff!
Ability to
hold organic
matter
Low – not enough water
High – some air and
some water available
Low – not enough air
Poor – particles pass
through the big gaps
easily
Good
Poor – particles wash of
the surface without
penetration.
Primary
productivity
Very Limited
High
Some but Limited
Soil Degradation - Overgrazing
Allowing animals to eat more than the area can
sustainably produce. Exposes the soil to erosion as
animals start to eat not only leaves but also roots. Rabbits
and goats are big culprits
Microsoft Clip art
Soil Degradation - Deforestation
Increased need for farm land and wood for building leads
to more trees being cut down than are being planted.
This removes top cover and roots, reduces humus build
up and therefore leads to soil deterioration and erosion.
Microsoft Clip art
Soil Degradation – unsustainable agriculture
Mono-culture (growing only one crop)
year after year removes the same
nutrients from the soil each year. These
nutrients (eg. Nitrates) can only be
replenished by fertilizers.
This is called Overcropping.
Growing crops with open ground in
between the rows increases erosion.
Excessive use of pesticides leads to a
build up of poisons in the soils.
Microsoft Clip art
Soil Degradation - Irrigation
Areas that need irrigation normally have high
evaporation rates. Higher evaporation than precipitation
causes water to move up the soil column bringing
dissolved nutrients to the surface. This can cause
salinization.
Microsoft Clip art
Soil Degradation - Erosion
Poor farming practices such as
ploughing in the directions of
slopes, burning stubble after
harvest and overgrazing can
remove the soils protection
from wind and rain erosion.
(1930’s dust bowl) Without
roots or protection the ‘A’
horizon can be removed.
Microsoft Clip art
Soil Degradation - Toxification
The build up of toxic / poisonous chemicals in
the soils can kill beneficial organisms in the
soil (eg. Earthworms, bacteria and fungi).
Microsoft Clip art
Soil Degradation - Salinization
Often caused by excessive use of irrigation.
The land becomes too salty for any plants to
grow on it.
Microsoft Clip art
Soil Degradation - Desertification
When previously productive
land becomes a desert.
Often caused by
overgrazing eg. Sahel region
over the Sahara in the 80s.
Microsoft Clip art
Basic Facts on Desertification
•Desertification occurs through land degradation in arid, semi-arid and dry sub-humid
areas resulting from various factors, including climatic variations and human activities.
•Desertification is not, as commonly thought, the actual expansion of existing deserts.
•Desertification affects nearly one billion people, or one-sixth of the world's population.
•Desertification is occurring in 70 per cent of all drylands, or one-quarter of the total land
area of the Earth.
•Desertification causes widespread poverty, and is responsible for much of the migration
in the developing world.
•Desertification is responsible for the degradation of 73 per cent of the world's rangeland.
•Each year, the planet loses 24 billion tons of topsoil. Over the last two decades, enough
has been lost to cover the entire cropland of the United States.
•Desertification is especially severe in Africa, where two-thirds of the continent is desert
or drylands, and where 73 per cent of its agricultural drylands are already seriously or
moderately degraded.
•Asia contains the largest amount of land affected by desertification of any continent-just
under 1,400 million hectares.
•Nearly two-thirds of Latin America's drylands are moderately to severely desertified.
Desertification costs the world more than $40 billion a year in lost productivity.
http://www.nyo.unep.org/action/15f.htm
Soil Remediation - Enhanced Soil Cultivation Kieran
• Definition- Cultivation is the act of digging into or
cutting up an existing soil bed in order to better
prepare it for planting.
• For farmers, cultivation typically means running a
tractor over their field with a plow or disc to break
up the soil's surface, this is done before planting and
breaks up and buries the remains of the previous
seasons crop (rather than burning it off) to add to
the humus in the ‘a’ horizon.
http://image.shutterstock.com/di
splay_pic_with_logo/86680/8668
0,1226037332,2/stock-photosoil-cultivation-at-the-smallrural-farm-20115355.jpg
Reason for Cultivation
Under adverse conditions a
soil may become compacted
and lose its structure. The
little pockets of air beneath
the surface are squeezed
together so that water and
nutrients can no longer
move through the soil. It
becomes more difficult for
the crops roots to grow.
When cultivating the soil, it is essential for the farmers to add in
other soils that keep the cultivated soil healthy and keep its
nutrients.
Advantages
http://photogallery.nrcs.
usda.gov/Preview/IA/p0
000003521.jpg
• Cultivating crops regularly can reduce unnecessary herbicide
applications.
• Cultivation between crop field rotations will decrease weed
establishment, especially when growing perennials.
• Organic farmers should cultivate the soil before planting
crops.
• Increase infiltration of water
Disadvantages
• Soil cultivation requires lot of time, money,
and energy.
• Ploughing of wet soils can lead to a smearing
of the plough sole.
• If the furrows run down hill it can lead to
increased erosion of the top soil.
Sources
• http://www.landscapeamerica.com/landscapes/soil/cultivation.html
• http://www.wisegeek.com/what-is-soilcultivation.htm
• http://www.articlesbase.com/gardeningarticles/advantages-of-hydroponics-over-soilcultivation-3874732.html
• http://www.betuco.be/CA/Soil%20cultivation
%20and%20tillage%203-3.pdf
Soil remediation - Terracing 1- Kai
• Terracing is the
replacing of the slope
with a series of
horizontal terraces,
separated by walls.
• Farming to cultivate
slope land
• Used to farm on hilly or
mountain terrain
• Rice field is most
commonly found in
these terrains
http://biagkensiak.files.wordpress.com/2009/12/banaue-rice-terraces-715556.jpg
Soil remediation - Terracing 2
• Can retain water
• Does not push
the water and soil
damaging other
things
• Prevents soil
erosion
http://www.megethos.com/albums/Kor-269%3Bula,-Croatia/OliveTerracing.jpg
http://en.wikipedia.org/wiki/Contour_plowing
Soil Remediation- Contour plowing - Dillon
Contour plowing (or contour ploughing) or contour farming is the farming
practice of plowing across a slope following its elevation contour lines.
The rows formed slows water run-off during rainstorms to prevent soil erosion
and allows the water time to settle into the soil.
In contour plowing, the ruts made by the plow run perpendicular rather than
parallel to slopes, generally resulting in furrows that curve around the land and
are level.
A similar practice is contour bunding where stones are placed around the
contours of slopes.
http://www.cottoninc.com/Soil-Resources/ControllingSoil-Erosion/images/ContourPlowing.jpg
http://www.uwsp.edu/geo/faculty/ozsvath/images/contour%20plowing.jpg
Soil Remediation - Set-Aside 1 - Carl
Introduced as political measure
in 1988 by European Union.
Became Compulsory in 1992.
Entails that farmers have to put
aside an amount of their
harvested land and not use
them for agricultural
purposes.
Farmers are paid for not utilizing
the land.
Environment develops, as it has
been set aside allowing the
ecosystem to balance out.
Provides habitats for biological
control organisms.
A set aside strip between two fields.
Image by - Walter Baxter
http://www.yourlocalweb.co.uk/images/pictures/24/48/
a-set-aside-strip-between-two-fields-241790.jpg
Soil Remediation – Set Aside 2
• Main Goals:
– Reduce surplus in
Europe (Grain
Mountains)
– Deliver
environmental
recovery after
damage to
ecosystems as a
result of
intensification of
agriculture
• Initial results:
– Surplus decreased
from 15% to 10%
(1992-2000)
– Surplus is now at
0%
A set aside field
Image by Walter Baxter
http://www.yourlocalweb.co.uk/images/pictures/21/93/set-asidefield-216481.jpg
http://www.strandtea.com/shop/images/uploads/inline-images/sustainable-agriculture.jpg
Soil remediation – Multi Cropping - Sarah
www.strandtea.com
Soil remediation – Multi Cropping 2
Mixed cropping is growing of two or more crops
simultaneously on the same piece of land. This
type of cropping leads to an improvement in the
fertility of the soil and hence, increase in crop
yield because when the two crops are properly
chosen the products and refuse from one crop
plant help in the growth of the other crop plant
and vice-versa.
Mixed cropping is an insurance against crop failure
due to abnormal weather conditions.
Examples of Multi Cropping
•
•
•
•
•
•
•
•
•
Soyabean + Pigeonpea
Maize + udad dal (Black gram)
Pigeonpea + Mung dal (Green gram)
Groundnut + Sunflower
Sorghum + Pigeonpea
Wheat + Chickpea
Barley + Chickpea
Wheat + Mustard
Cotton + Groundnut
sources
• http://www.tutorvista.com/content/biology/b
iology-i/sustainable-agriculture/mixedcropping.php
• http://en.wikipedia.org/wiki/Multiple_croppin
g
Soil Remediation – Conditioning Yoatzin
What is a soil conditioner?
• A material added to soil to enhance plant
growth.
What is the purpose?
• The conditioner corrects the soil’s deficiencies
in structure or nutrients. Eg. Acid soils can be
neutralized by adding alkali.
• Other forms of conditioning include adding
lime, peat (to nutrient poor soil), diatomaceous
earth, clay (to sandy soils), vermiculite (to clay
soils), hydrogel, and shredded bark and soil
inoculant,
Soil Remediation –Hydroponics 1- Allen
http://www.blackmaxozone.com.au/img/assets/gary/gel%20hydroponics%20alberton%20qld%203.jpg
Soil Remediation –Hydroponics 2
the process of growing plants in sand, gravel, or liquid, with added nutrients but without
soil.
First discovered in the 18th century
http://www.indigrowhydroponics.co.uk/wordpress/wp-content/uploads/2010/07/Omega-Indoor-Hydroponic-Gardens-2.jpg
Soil Remediation –Hydroponics 3
Advantages
• No soil is needed
• The water stays in the system and can be
reused - thus, lower water costs
• It is possible to control the nutrition levels
in their entirety - thus, lower nutrition
costs
• No nutrition pollution is released into the
environment because of the controlled
system
• Stable and high yields
• Pests and diseases are easier to get rid of
than in soil because of the container's
mobility
http://www.barstoolu.com/wp-content/uploads/2011/01/thumbs-up.jpg
Soil Remediation –Hydroponics 3
Disadvantages
• The hydroponic conditions
(presence of fertilizer and high
humidity) create an environment
that stimulates salmonella
growth.
• overwatering of soil based
plants.
• hydroponic plants require
different fertilizers and
containment system
Soil remediation-Crop Rotation -Isabella
Crop rotation is the practice of
growing a series of dissimilar types of
crops in the same area in
sequential seasons.
http://www.betterhensandgardens.com/wp-content/uploads/Crop-Rotation.jpg
http://www.kings.co.nz/site/kingsplant/images/Kings_3yr_crop_rotation_Main_Sep_08.jpg
Soil remediation - Crop Rotation 2
• balances the fertility
demands of various crops to
avoid excessive depletion of
soil nutrients.
• can improve the soil structure
and the fertility – eg.
leguminous plants have
bacteria in their roots that ‘fix
nitrogen’ (add nitrates) to the
soil.
• avoids a decrease in soil
fertility.
• farmers found that growing
the same crop on the same
land again and again, leads to
disease buildup.
http://wordpress.yell.com/gardens/files/2010/03/crop-rotation2.jpg
http://lh4.ggpht.com/_GpsVorlbuKM/R2UwwRyZO9I
/AAAAAAAABSU/vbHOkevnVAg/PICT0005.JPG
Soil Remediation - Biological Pest Control Kei
The reduction of pest populations which predate, parasitize, or eat wanted
plants using their natural enemies.
Cases that have been looked at
1. Dragonflies vs. Mosquitoes
Mosquitoes infest waters in which plants grow,
They also feed on nectar or plant juices– they are
Therefore pests and threats to many plants.
Their predators, the Dragonflies, are reinforced
As they eat mosquitoes both in their larvae form
And their adult form.
http://www.richardseaman.com/Wallpaper/Nature/Damselflies/
OrangeDamselflyEatingMosquito.jpg
“Biological Pest Control." Wikipedia, the Free Encyclopedia. Web. 01 Apr. 2011.
<http://en.wikipedia.org/wiki/Biological_pest_control#Negative_results_of_biological_pest_control>.
2. Ladybugs vs. Aphids
Aphids are small pests that come in big populaTions. Their influence can decrease growth
Rates of plants and yellow their leaves.
Farmers support ladybug populations to decrease
The numbers of this pest.
http://www.ladyb
ugindoorgardens.com/imag
e/tnail/ladybug.jpg
Advantages/Disadvantages
•
The process is, to some degree, natural.
•
The process is more effective then chemical
pesticides as pesticides can be toxic and they sometimes kill of the natural
predators of these pests.
• Animals are unpredictable and this can pose as a threat (ex: the mongoose
was introduced to hawaii to control rat populations but it preyed on
endemic Hawaiian birds more often than rats.)
"Aphid." Wikipedia, the Free Encyclopedia. Web. 01 Apr. 2011.
<http://en.wikipedia.org/wiki/Aphid#Effects_on_plants>.
Soil Remediation- Reforestation 1What is it? - Kay-Li
• restocking of existing forests
and woodlands which have
been depleted
• Undoing the effects of
deforestation
• can be used to improve the
quality of human life by
soaking up pollution and dust
from the air and providing
parkland.
http://en.wikipedia.org/wiki/Reforestation
http://www.treehugger.com/peru-national-reforestation-campaign.jpg
Soil Remediation- Reforestation 2
Britain Case Study
• Planting 23,000 hectares of forest every
year for the next 40 years
-lower the island nation's greenhouse
gas emissions by 10%.
• The tree-planting effort would also raise
Britain's total amount of forest cover
from 12% to 16% by 2050.
-provide habitat for wildlife
-add new flood protections to
increasingly vulnerable areas
http://www.treetopasia.com/wp-content/uploads/2008/10/reforestation-work-for-primate-habitat.jpg
http://news.mongabay.com/2009/1125-hance_britain.html
•
Soil Remediation- Reforestation 3
Philippine Case Study
The Issue:
-Primary forests in the Philippines are being destroyed due
to both logging and agricultural expansion
-Significantly decreasing the Philippine's natural resources
-This type of deforestation is leading to a variety of global
and local changes
-Forest cover has decreased by 56% in the postwar period
-High concentration of a certain tropical hardwood
(indigenous to Southeast Asian countries), are exported
globally for high commercial return.
(Approx. 70% of all tropical wood products on global
market after WWII originated in Southeast Asia; this
proportion had risen to 83% by the mid 1980s.)
http://www.pia.gov.ph/press/image/070723-r7-tree4life.jpg
http://www1.american.edu/TED/philwood.htm
If you can’t remediate the soil maybe
you could use GM Crops
Kristen Shull
http://www.lifeinthemixtalk.com/wp-content/uploads/2009/08/gm-crops.jpg
What is it?
• Crops that have been
genetically improved
by scientists
• Good genes taken
from one crop are
placed in another to
create a more reliable
crop
http://www.ifood.tv/files/images/editor/images/Are%20The%20Benefits%20Of%20GM%20Crops%20Often%20Overstated.gif
Advantages
• Bigger crop yields
• More resistant to disease/ pests – so the
farmers need less pesticides therefore
reducing toxification.
• Need less nutrients/ water – so the farmers
need less irrigation and less fertilizer therefore
reducing salinization.
• Stronger
• Grow faster
• More vitamins/ minerals- eg golden rice
• 3rd world countries get more food
• Better use of land
• No evidence of harm (safe)
• Resist salt content in soil so can grow in
degraded salinated soils
http://img.dailymail.co.uk/i/pix/2007/04_03/gmsoyaDM0305_468x346.jpg
Salinity
• Caused by intense agricultural practice
• Stresses crops (prevention of water
absorbation/ changed ion concentration
damages cell functions)
• GM crops resist it due to more glycinebetaine
(natural substance created by salt-fighting
plants)/ a protein able to filter out sodium
http://www.learner.org/courses/envsci/visual/img_med/california_fields.jpg