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Lecture 23

AGR 2050 Lecture Notes - Lecture 23: Soil Health, Food Web, Soil Structure

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Course Code
AGR 2050
Clarence J Swanton

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Monday, March 19, 2018
Food Webs
Food chains to food webs
Feeding connections of “what-eats-what”
Non-random associations
Energy is transferred through trophic levels
o Thermal Dynamics: energy cannot be created nor destroyed
o Soil: energy flows throughout the system
Till vs. No-Till
Chisel plowed field:
o Can see above ground
o But cannot see underground
Conventional Till
o Sunk in = aeration
o Causes runoff (to places you don’t want it to go)
o Energy flow completely different
o Better soil structure
Example: cotton underwear comparison
o After two months of the soil
o Tilled: some holes, but still intact
o No-Till: disincarnated
Soil Health
Soil health is often equated to the diversity & activity of the soil microbiome
A single teaspoon (1 gram) of rich garden soil can hold up to one billion
bacteria, several yards of fungal filaments, several thousand protozoa, &
scores of nematodes
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All the linkages that hold soil together (destroy structure with tilling)
Soil is made up of living organisms, that move energy
Tropic Dynamics
The basic process in trophic dynamics is the transfer of energy from one part
of the ecosystem to another
All function & all life within an ecosystem is dependent upon the utilization of
solar energy
Solar energy is transformed by photosynthesis into complex structures of living
Producers (auto-trophic plants) transform energy via photosynthesis
Heterotrophs: an organism that cannot fix carbon & uses organic carbon for
Consumers: feed upon the surplus of energy
Decomposers: break down dead or decaying organisms, tissues (dissipate
the remaining energy)
o Examples: moulds, worms, bacteria, & fungi
Food chains are directional paths of trophic energy or, equivalently
sequences of links that start with producers & ends with decomposing
Often thought of as a linear sequence of links in a food web (this may be an
over simplification)
Food Web
A network of food chains or feeding relationships by which energy & nutrients
are passed on from one species of living organisms to another
A conceptual model of feeding relationships among organisms within an
A collection of food chains
Commented [A1]: Cannot be created OR destroyed
Commented [A2]: Cannot produce, but they can
Commented [A3]: Recyclers
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