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Soil Foundation for Land Ecosystems


Interaction among organisms detritus and mineral particles of the soil ... feed on detritus, soil organic matter (SOM), and the microbes living on these tissues ... – PowerPoint PPT presentation

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Title: Soil Foundation for Land Ecosystems

Soil Foundation for Land Ecosystems
  • Ch 8

  • 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)

  • 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-

  • 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

  • Soil Characteristics
  • Soil profile
  • five major layers
  • O humus, surface litter, decomposing plant
  • 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

  • Soil texture
  • Describes the size of soil particles
  • As rock weathers it breaks down into smaller
  • 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

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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

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

  • 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

  • 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

  • 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

  • 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

Notice the distribution for Ultisols.
  • 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,

  • 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

  • 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

  • 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

  • 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

  • Relative acidity
  • pH different plants are adapted to different pH
  • Most plants do best with a slightly acid pH

  • 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

  • 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

  • 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
  • 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.

  • 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
  • Topsoil is imperative for growing plants. B
    horizon soil is only capable of growing 10-15
    of what can be grown on topsoil

  • Interactions
  • Mycorrhizae
  • Fungi that have a symbiotic relationship between
    the roots of a plant and the rhizomes of certain
  • 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

  • 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
  • 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
  • farmers use soil and water conservation

  • Erosion the loss of topsoil
  • Soil and humus carried away by wind and water
  • Occurs any time soil is bared and exposed to the
  • 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

  • Splash, sheet and gully three types of erosion

  • 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

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

  • Causing and correcting Erosion
  • Qvercultivation
  • no till traditional method, plow to control
  • 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

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

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

  • 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

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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)

  • 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

  • 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

  • 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

  • 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

  • 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

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

  • 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
  • Keep farm economically viable
  • Use contouring, crop rotation, terracing, smaller
    equipment. Reduced amount of chemicals or none at

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

  • 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
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