Soil Foundation for Land Ecosystems

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Soil Foundation for Land Ecosystems

• Ch 8

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• 1. Soil and Plants
• a) What is soil?
• Interaction among organisms detritus and mineral
  particles of the soil
• Nutrients from detritus are released and
  reabsorbed by producers (plants)

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• Detritus feeders and decomposers constituted a
  biotic community of organisms
• Can include animals, bacteria, fungi, algae,
  atinomytes, mycorrhizae
• feed on detritus, soil organic matter (SOM), and
  the microbes living on these tissues-

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• burrowing creates macropores- enhances drainage
  and aeration
• -casts increase aggregate stability, provide
  mesopores for water retention
• these organisms require certain temperatures and
  soil moisture to function maximally
• Facilitates the transfer of nutrients

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• Soil Characteristics
• Soil profile
• five major layers
• O humus, surface litter, decomposing plant
  material
• A topsoil. Mixed humus and mineral soil
• E zone of leaching less humus, minerals that
  are resistant to leaching
• B subsoil, accumulation of leached minerals,
  iron and aluminum oxides
• C weathered parent material

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• Soil texture
• Describes the size of soil particles
• As rock weathers it breaks down into smaller
  fragments
• Sand particles from 2 0.02 mm in size
• Silt 0.02-0.002mm
• Clay-anything smaller than 0.002 mm
• Clay particles are able to become suspended in
  water.

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• Soil classes - ,many many types of soils. These
  are four of 11 orders. Soils are classified much
  in the same way animals and plants are classified

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• Mollisols fertile, dark soils found in
  temperate grassland biomes the worlds best
  agricultural soils

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• Oxiols soils of the tropical rain forests
• Layer of iron and aluminum oxides in the B
  horizon, little O horizon
• Of limited agricultural value, most of the
  nutrients are in the living plant matter
• If the forests are cut a few years of crop growth
  can be obtained

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• Alfisols
• Widespread, moderately weathered forest soils
• Not deep
• well developed O, A, E and B horizons
• suitable for agriculture if they are supplemented
  with organic matter or mineral fertilizers

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• Aridisols
• Drylands and desert soils
• Relatively unstructured verticallythin and light
  coloredirrigation on these soils usually leads
  to salinization as high evaporation rates draw
  salts to the surface where they accumulate

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• Soils in our area are classified as ultisols.
• The central concept of Ultisols is that of soils
  that have a horizon that contains an appreciable
  amount of translocated silicate clay (an argillic
  or kandic horizon) and few bases (base saturation
  less than 35 percent). Base saturation in most
  Ultisols decreases with depth

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Notice the distribution for Ultisols.
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• Soil and plant growth for best growth, plants
  need an optimal root environment
• Mineral nutrients and nutrient holding capacity
• For a plant, there are nine major elements
  essential for healthy growth these are called
  macronutrients. They are carbon, hydrogen, and
  oxygen (which are all three derived from air and
  water) and nitrogen, phosphorus, potassium,
  calcium, sulfur, and magnesium (from the soil).
  PO3-4 potassium (K), calcium (Ca2) , S2-, Mg2,
  Ca2

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• Nutrients are supplied initially by the breakdown
  of rock, secondarily, by the recycling of
  nutrients from detritus
• Leaching nutrients that are washed from the
  soil as water moves through it. Soils have
  different abilities to hold nutrients, called the
  nutrient holding capacity or cation exchange
  capacity

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• Fertilizer nutrients are removed from the soil
  with each crop. Nutrients absorbed by plants are
  contained in the harvested material fertilizers
  are used to replace nutrients
• These can be organic having plant or animal
  wastes or both, manure and compost
• Or inorganic without any organic material
  included these are much more prone to leaching
  than organic fertilizers

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• Water and water holding capacity water is
  pulled from the soil by the roots of plants in a
  process called transpiration
• Clay and humus have very high nutrient holding
  capacities. Cation exchange

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• Aeration
• There needs to be air (oxygen) in the pore spaces
  in the soil for roots to breathe
• Soils should be loose and porous to allow the
  diffusion of O into and CO2 out of the soil.
• Over watering fills air spaces
• Compaction (foot traffic, heavy machinery on
  soils) reduces infiltration and increases runoff

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• Relative acidity
• pH different plants are adapted to different pH
  ranges.
• Most plants do best with a slightly acid pH
  (5.0-6.5)

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• Salt and water uptake
• If there is a buildup of salt in the soil, plant
  roots cannot take up water (hypertonic solution,
  water will flow OUT of the plant roots)
• Some plants have special adaptations that allow
  them to grow in salty situations
• No crop plant has this adaptation

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• The soil community
• Detritus soil organisms, humus and topsoil
• Detritus dead leaves, roots, accumulation on
  the surface of soil
• Supports a food web of organisms, bacteria,
  fungi, Protozoans, mites, insects, etc.
• Most important are the bacteria there are
  millions in a gram of soil

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• Humus
• The part of the detritus that is left after the
  CO2, O2,water and mineral nutrients are released
• The dark brown stuff at the bottom of the O
  horizon.
• Black or dark brown spongy material remaining in
  a dead log
• Holds lots of water and nutrients, as much as 100
  times better than clay
• Composting fostering the decay of organic
  wastes under controlled conditions what you
  should do with your kitchen vegetable matter,
  grass clippings and weeds.

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• soil structure
• refers to the arrangement of soil particles
• earthworms process the soil to digest mineral and
  detritus on or in the soil.
• Castings are soil particles containing minerals
  and humus that are glued together.
• Burrowing is good for the soil. Aerates the
  soil, allows infiltration, makes soil more
  workable
• Topsoil is imperative for growing plants. B
  horizon soil is only capable of growing 10-15
  of what can be grown on topsoil

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• Interactions
• Mycorrhizae
• Fungi that have a symbiotic relationship between
  the roots of a plant and the rhizomes of certain
  fungi
• They penetrate the detritus, absorb nutrients,
  transfer them directly to the plant.
• No loss due to leaching

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• soil enrichment or mineralization
• the bulk of the detritus which supports the soil
  organisms is from green plant producers
• green plants support the soil organisms
• the soil organisms create the chemical and
  physical soil environment that is most beneficial
  to the growth of the producers

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• humus
• green plants protect the soil
• protection from erosion (breaks the impact of
  rain drops)
• reduces water loss maintain an organic mulch
  around plants in the garden also adds to
  detritus
• humus generally decomposes about 2-5 of its
  volume each year, more in the tropics, less in
  the arctic
• as humus content declines, water holding capacity
  declines, infiltration and aeration declines
• collapse of topsoil known as mineralization of
  the soil
• what is left is gritty sand with not much
  detritus and humus

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• Soil Degradation
• GLASOD (Global Assessment of Soil Degradation
  map) 1987-1990 very little data has been
  validated, cited again and again
• Burkina Faso
• one of the poorest and most densely populated
  countries in West Africa
• supposedly has very degraded soil
• but has been able to increase agricultural yields
  during the last 40 years while its pop has
  doubled
• farmers use soil and water conservation

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• Erosion the loss of topsoil
• Soil and humus carried away by wind and water
• Occurs any time soil is bared and exposed to the
  elements
• Any time rain falls in a natural ecosystem, the
  fall is dissipated by loose topsoil or
  vegetation. It filters into the soil.
• Vegetation holds the soil, dissipates rain drop
  impact, lies down and allows water to flow over
  it without washing away soil. Grass forms
  mat-like roots that hold soil well. Doesnt
  allow wind to carry soil away
• Eroded soil is less able to support the regrowth
  of vegetation, causes more erosion a vicious
  cycle

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• Splash, sheet and gully three types of erosion

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• Desert pavement
• Soil is deflated, wind blows finer particles away
  leaving sand and gravel behind

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• Drylands and desertification
• As clay and humus are removed, the nutrient and
  water holding capacity is reduced, nutrients are
  bound chemically to these particles, remove them
  and you lose the ability of the soil to hold the
  nutrients

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• UNCCD United Nations Convention to Combat
  Desertification
• Funding of projects to reverse land degradation
• Impart knowledge on effective drylands
  agricultural practices

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• Causing and correcting Erosion
• Qvercultivation
• no till traditional method, plow to control
  weeds
• exposes soil to wind and water
• after harvest the soil is exposed again maybe for
  the whole winter
• subject to splash erosion
• runoff
• weight of tractors causes compaction
• crop rotation is sustainable, plant high cash
  crop every third year, plant hay, then clover to
  fix nitrogen and adds organic matter

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• fertilizer
• chemical fertilizer lacks organic matter
• can plant a cash crop every year but it causes
  mineralization
• excess fertilizer is leached into the soil, runs
  off into waterways and causes pollution

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• NRCS
• Contour strip cropping
• shelter belts belts of trees around fields to
  break wind and protect the soil from erosion

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• Overgrazing
• Animal stock eats too much, removes too much
  vegetation, exposes soil to erosion
• Has led to soils that cannot support grasses only
  supports sagebrush, mesquite, juniper
• Has upset the ecosystems of the range reduced
  biodiversity, altered feeding and breeding
  patterns of birds small mammals, reptiles and
  insects

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• Public lands
• Rangelands are public lands not owned by the
  people who own the herds
• If the land were owned by the owners of the
  animals, the incentive would be to take care of
  the land
• The incentive is for all to keep grazing
• Fees charged by the US Bureau of Land Management
  about on fourth what would be charged to graze on
  private land
• Lots of political pressure to block any attempts
  to raise grazing fees
• NRCS (Natural Resource Conservation Service)

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• Deforestation
• A study in New Hampshire found that in a forested
  area clear cut , runoff was increased by two fold
  and nutrient leaching many fold
• most of the nutrients held in the plant materials
• particularly devastating on tropical soils
• parent materials maximally weathered
• when forests are cut, thin layer of humus washes
  away

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• Global loss
• 2.2 million acres cleared per year in the 1990s
• almost an area three times the size of France
• very poor use of land for agricultural purposes

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• The other end of the erosion problem
• When water flows from land, carrying sediment it
  pours into streams and rivers, overfills them,
  causes flooding, sediments carried into streams
  and rivers, clogs channels, exacerbates flooding,
  water doesnt flow into the soil to replace
  groundwater

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• Irrigation and Salinization
• Irrigation 67 million acres total under
  irrigation in the US
• Flood very wasteful, most water evaporates or
  percolates beyond the root zone
• Center pivot water is pumped from a central
  well that pivots around the well, provides
  irrigation for 10 million acres of farmland

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• Salinization
• accumulation of salts in and on the soil, due to
  irrigation with water containing at least 200
  5ppm dissolved salts
• also occurs when dryland soils are irrigated,
  dissolves soluble minerals present in the soils
• considered a form of desertification

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• Lost land
• Due to salinization and waterlogging, loss of 3.7
  million acres worldwide.
• In the US a problem in the lower Colorado River
  basin
• 400,000 acres rendered unproductive
• salinization can be reversed if sufficient water
  is applied to leach the salts down through the
  soil

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• Conserving the soil
• Public policy and soils
• Subsidies because of subsidies, US taxpayers
  support agriculture at a level of 74
  billion/year subsidies are bad for the
  environment, encourage excessive use of
  pesticides, and fertilizers, reduce crop
  rotation, promote drawdown of groundwater
  aquifers through irrigation
• Sustainable agriculture
• Maintain productive topsoil
• Keep food safe and wholesome
• Reduce the use of chemical fertilizers and
  pesticides
• Keep farm economically viable
• Use contouring, crop rotation, terracing, smaller
  equipment. Reduced amount of chemicals or none at
  all

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• Conservation reserve program
• Payment to farmers to keep land out of crops.
• Saves topsoil from erosion
• Farm bills

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• Helping individual landholders
• FARM Farmer-centered Agriculture Resource
  Management Cooperative venture of 8 Asian
  countriessupport improved sustainable
  agricultural resource management and the
  attainment of household security through
  innovative approaches in rainfed areas of Asia
• Farmer Field Schools teach integrated soil
  management, farmers learn solutions for their own
  farms