Plant & Animal Life in the Soil

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Plant Animal Life in the Soil

• Original by Casey Osksa
• Modified by Georgia Agricultural Education
  Curriculum Office
• July, 2002

2
What kinds of plants and animals live in the soil?

• 1) Bacteria most numerous and important
• single celled plants, can reproduce in 20-30
  minutes and may decrease rapidly in in favorable
  conditions
• a soil which has 5 O.M. can have 3 1/2 tons of
  bacteria per acre
• crops require free oxygen or aerated conditions
  in the soil
• anaerobic bacteria (do not need free oxygen) get
  their oxygen from chemical reactions

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What kinds of plants and animals live in the soil?

• 2) Actinomycetes the size of bacteria, but some
  resemble molds
• can live under drier conditions than bacteria,
  abundant in sod
• among the most important agents of the soil in
  the breakdown of dead plant materials, including
  cellulose
• responsible for characteristic smell of freshly
  tilled soil

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What kinds of plants and animals live in the soil?

• 3) Fungi most are too small to be seen by the
  naked eye, except for yeast, molds, mushrooms,
  puffballs, and toadstools
• fungi do not have chlorophyll and must get their
  food from organic substances

5
What kinds of plants and animals live in the soil?

• 4) Algae contain chlorophyll
• ex seaweed, scum-forming algae on ponds
• soil algae are too small to be seen with the
  naked eye, but in large numbers can give soil
  surface a green color
• favor damp soil that is exposed to the sun
• believed to be able to fix free nitrogen from the
  air in the soil, valuable to rice production

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What kinds of plants and animals live in the soil?

• 5) Protozoa minute animals found in the soil,
  smallest form of animal life
• must live in a water film

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What purpose do microorganisms have?

• decay plant residue (straw etc.)
• make free nitrogen in the air available to plants
• break down nutrients needed by plants
• break down cellulose
• much of the food in the soil is not available to
  the plant, until microbes break them down

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What is Nitrogen Fixation?

• the process of changing free nitrogen from the
  air into plant useable nitrogen by bacteria
• two types of nitrogen fixing bacteria
• 1) attached to the roots of legumes
• 2) live freely in soil (few)
• a column of air 1" square weighs 14.7 pounds.
  Our atmosphere is about 75 nitrogen. How many
  pounds of nitrogen are in the air above one acre?

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How do Nitrogen Fixing nodules form?

• bacteria enter the single-celled root hairs where
  they multiply rapidly due to favorable
  conditions, the colonies then form into nodules,
  usually in bunches

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What are false nodules?

• insects may injure legumes causing false nodules

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What is Inoculation?

• when a legume plant is grown for the first time,
  it is essential to expose the seed to Rhizobium
  bacteria (nitrogen fixing) before planting

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How much nitrogen is added to the soil by
bacteria?

• free soil bacteria add 10-50 lbs./yr.
• nodule bacteria add 50-100 lbs./yr.
• may not be a net gain due to nitrogen in
  harvested crop
• gene splicing may yield a corn plant with
  nitrogen fixing qualities. This would save the
  producer money and reduce the need for petroleum
  (most commercial fertilizers are made from
  petroleum)

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What are some of the harmful effects of soil
microorganisms?

• bacterial diseases potato and tomato wilt,
  mildews, blights, dry rot
• microbes compete for food with the crop, it there
  are any shortages of nutrients this could harm
  the plant
• nitrogen tie-up

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What are favorable conditions for soil
microorganisms?

• food, temperature, moisture, acidity, and
  aeration most are similar to plants
• most are injured by direct sunlight except algae
  (chlorophyll)

15
What problems result from soil management
practices?

• conservation tillage reduces microbe activity,
  thus fertilizer must be added to feed the
  microbes and speed decomposition (add 20 N/ton
  of straw)

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Why do producers summer fallow?

• conserve water
• conserve nitrogen

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What are some of the higher forms of animal life
in the soil?

• slugs snails feed on the surface, favor damp
  shady conditions
• arthropods insects (ants, centipedes) most feed
  on decaying O.M.
• nematodes (eelworms) abundant in soils, three
  groups
• 1) feed on plants
• 2) feed on other life forms
• 3) feed on decaying O.M. (earthworms) up to 500
  lbs per acre, aerate soil, allow water to
  penetrate, excrement is good plant food

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What are some of the higher forms of animal life
in the soil?

• rodents, gophers, squirrels, prairie dogs most
  are considered a nuisance. Burrows are similar
  to those of worms, but can be a menace

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What are some of the higher forms of plant life
in the soil?

• plant roots hold down surface soil
• break up subsoil
• provide O.M.
• add minerals, air, and water
• channels for air water penetration
• loosen soil