Underground Grazing

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Underground Grazing
Joel Gruver Soil Science NCSU
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Two perplexing phenomena have long puzzled soil
ecologists
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Mean residence times for microorganisms are
hundreds of times longer in soil than in
laboratory cultures.
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The metabolic potential of soil microbial
communities greatly exceeds available organic
substrates.
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Why do microorganisms behave so differently in
soil than they do in a petri dish ?
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The Sleeping Beauty Paradox
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Most of the pores where soil microorganisms
reside are either environmentally suppressive or
lacking in appropriate substrates.
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Soil microorganisms are very limited in their
ability to move within the soil matrix.
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As a result, most of the microorganisms in soil
are in a dormant state
waiting
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for their Prince Charmings to arrive
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What is the drilosphere ?
Zone of earthworm influence  burrows, galleries,
diapause chambers, surface and subterranean
casts, middens Functionally similar to
rhizosphere and detritusphere
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Diapause aka Aestivation
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Middens
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http//www.sciencebuddies.org/mentoring/project_id
eas/PlantBio_p002.shtml?fromHome
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Earthworm functional continuum Epigeic ?
Anecic ? Endogeic
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Which burrows were made by an endogeic ?
Capowiez et al. 2003)
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Earthworm Taxonomy More than 3500 species of
earthworms have been identified worldwide   12
families of earthworms in the US and Canada
150 total species   45 are exotic species 25 are
exotic Lumbricids from Europe  
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Earthworms in North Carolina An extensive survey
(sites in 80 counties) was conducted by Dr. John
Warren Reynolds in the early 1990s. 42 species of
earthworms were found. The results of this survey
and surveys of the earthworms present in many
other states can be found in the journal
Megadrilogica .
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Peer-reviewed proceedings from a 1993
international conference. Topics discussed
include How has glaciation affected earthworm
distribution in North America ? How do native
and exotic species impact natural and
agroecosystems ? How has earthworm taxonomy
changed over time ?
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Native Earthworm genera in the SE
Sparganophilus
Bimatos
Eisenoides
Diplocardia
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Earthworm identification can be tricky !
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Earthworm anatomy
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Key features for identifying worms
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• Allolobophora chlorotica
• (Green Worm)
• Native to northern Europe
• Color varies from green to yellow, pink, or gray
• 30-70 x 3-5 mm
• Found in a wide range of soil types, mainly on
  wet, highly organic or polluted sites
• Endogeic, largely geophagous
• Matures at 120-130 days
• Casting and mating occur beneath the soil
• Facultative diapause
• Sluggish rolls into spiral when disturbed

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Amynthas diffringens (Snake worm, Crazy worm)

• Native to Southern Asia
• Widely distributed in warm climates, tolerates
  heat and drought
• 45-170 x 3-6 mm
• Parthenogenetic reproduction
• Endogeic, some detritivory at soil surface
• Very fast moving, lashes about when disturbed,
  often sheds "tail" which continues to lash about
  while the rest of the earthworm escapes

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• Aporrectodea trapezoides
• (Southern Worm)
• Paleartic origin
• Color variable, from slate gray to pink,
  flattenable posterior
• 80-137 mm x 3-7 mm contracted, 220 x 3-5 mm
  relaxed
• Parthenogenetic reproduction
• Dormancy spent rolled in a ball in an oval
  chamber
• Found in heavy or sandy soil
• Endogeic and mainly geophagous, but some
  individuals forage on surface detritus casting
  at soil surface
• Tolerates immersion in water

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Lumbricus terrestris, Night Crawler
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Eisenia fetida, Red wiggler
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(No Transcript)
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• How do earthworms move through soil ?
• Loose soil
• They insert their anterior tip into a pore,
  extend their setae to anchor most of their body
  and then exert radial and longitudinal pressure.
  A cycle of alternating contractions and
  relaxations thrusts their body forward.
• Dense soil
• They invert their pharynx, exude lubricating
  mucus and suck obstructive soil into their body.

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In 1881, Darwin reported that healthy earthworms
sometimes leave their burrows at night and embark
on a voyage of discovery

Surface migration by earthworms is a routine
activity aimed at dispersal and finding a mate.
Surface migration usually occurs during cloudy
moist conditions. Both anecic and endogeic
earthworms are active surface migrants.
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Earthworm sex
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Earthworm cocoons
http//soils.usda.gov/sqi/soil_quality/soil_biolog
y/images/CE8a-cocoon_LR_small.jpg
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• How do earthworms eat ?
• Earthworms eat by pulling food into their mouth
  with their prostomium (mouth) and pharynx which
  creates a very strong suction.
• The food is stored in the crop and then ground
  up into small digestible pieces in the gizzard.
• Earthworms need a gizzard because they do not
  have any teeth. Nutrients are absorbed in the
  small intestine.

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Internal anatomy
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How do earthworms affect pastures ?
Annual production of surface casts typically
ranges from 1 25 kg / m2
in temperate pastures.
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Effect of earthworms on SOM dynamics
Ingested soil
Fresh casts
Aging casts
Soil profile
Nutrient release
Shredding Assimilation
Physical protection
Acceleration of turnover
Lavelle (1997)
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Some effects of Aporrectodea caliginosa on the
properties of a pasture soil in Otago, NZ
(Stockdill, 1982)
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Studying earthworms in pasture systems
http//www.ucd.ie/agbiota/action/studies.htm
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Using plaster of paris to study earthworm burrows
Expelling earthworms using an irritant solution
(formalin, mustard)
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Collecting soil for 3 dimensional analysis of
earthworm burrows
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Expelling earthworms using an electro-shock
technique
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Optimizing the earthworm community in a pasture
soil Keep pastures well limed (maintain soil pH
gt 5.5) Minimize use of pesticides Fertilize to
increase pasture productivity Avoid ammonium
based fertilizers Maintain legumes
Irrigate Inoculate with earthworms
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How many worms should be in a pasture soil ?
Hendrix et al. (2003)
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When are earthworms most active ?
Syers et al. (1978)
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• A minimum target earthworm community
  (Lee, 1991)
• one or more anecic or anecic/epigeic species
  that make subvertical burrows, feed on litter and
  deposit casts at the surface
• one or more endogeic species that feed on dead
  roots and other subsurface organic matter and
  make randomly oriented burrows
• at least one species that makes deep burrows and
  can penetrate compact soil layers

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• New Zealand earthworm inoculation
  strategy
• Use turves from high earthworm areas to
  inoculate pastures that lack earthworms.
• Cut turf 200mm x 200 x 50mm and distribute 10m
  apart
• Distribute turves after a period of rain when
  soil is moist. Earthworms will move down into
  moist pasture soil as turves dry
• Identify source areas when soils are wet and
  earthworms are casting on the surface these may
  be near homesteads, trees, shelterbelts, areas
  that  are greener in spring. Source areas should
  have at least 500 earthworms per square meter for
  maximum establishment rates

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