AGR 2050 Lecture Notes - Lecture 23: Soil Health, Food Web, Soil Structure
1 May 2018
School
Department
Course
Professor
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
• No-till
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
• 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
organisms
• Producers (auto-trophic plants) transform energy via photosynthesis
• Heterotrophs: an organism that cannot fix carbon & uses organic carbon for
growth
• 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
organisms
• 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
ecosystem
• A collection of food chains
Commented [A1]: Cannot be created OR destroyed
Commented [A2]: Cannot produce, but they can
CONSUME
Commented [A3]: Recyclers
Document Summary
Food webs: food chains to food webs, feeding connections of what-eats-what , non-random associations, energy is transferred through trophic levels, thermal dynamics: energy cannot be created nor destroyed, soil: energy flows throughout the system. Commented [a5]: birds following the plow = no worms. In natural undisturbed systems decomposition & mineralization of plant. & animal detritus regulate the availability of nutrients for plant uptake or loss from the system: effect of tillage on nutrient cycling: Commented [a7]: linkages vary in strength (weak or strong) in non-random associations. Specifically associated with each other (danger that they may not re-form if broken) Commented [a9]: rate function over time, things that get effected temperature (seasons), concentrations (organic matter), ph, water. No-till soils are usually physically & chemically stratified with. Commented [a11]: leaky systems causes water flow, loss of nutrients, causes dead zones more nutrients near the surface. Commented [a12]: stratification of nutrients through the soil.
