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16 Cards in this Set
- Front
- Back
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aggregates or peds |
a group of primary soil particles that cohere to each other more strongly than to other surrounding soil particles |
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ped |
unit of soil formed by natural processes
clod formed artificially |
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soil structure |
the size, shape, and arrangement of aggregates and pores of the soils |
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soil tilth |
the physical condition of the soil in relation to plant growth |
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good structure of soil implies (2) |
1) suitable for max root growth and penetration
2) stable against forces causing degradation |
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What are the bonds holding aggregates together |
cation bridge - bring clay particles close together - the di and trivalent cations are tightly adsorbed and can neutralize negative surface charge -monovalent ion cause clay to repel
-hydrogen bonds
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expand of monovalent ions and aggregate bonds |
1. size - the large hydrated sodium ion does not get close enough to clay to effectively neutralize the negative charges
2. charge - the single charge on sodium is not effective in forming a bridge between clay particles |
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how do micro aggregates form |
by flocculation and cementation
they are more stable than macro aggregates: 1) less organic content, but it is older 2) stronger cohesion between clay particles
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what processes result in aggregation? (2)
how do you characterize aggregates? |
1) physical chemical processes - flocculation and cementation - volume changes from shrinking and swelling in clay - orgnaic matter, which is the major agent stimulating the formation and stabilization of granular.
2) biological processes - earthworms, enmeshment of particles by sticky networks of roots and hyphae, and organic glues produced by microbes
bulk density, total porosity, pore size distribution - use a sieve |
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aggregation = |
[% silt + clay] dispersed - % (silt + clay) aggregate |
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Location and function of macropores, mesopores, and micropores |
macropores (>75 um) - between pads, root channels, animal furrow - full of air at field capacity
mesopores (75um-30um) - inside of peds -filled with water at field capacity, also store water for plants
micropores (<30um) - soil matrix -filled with water at permanent wilting point, too small for plant to use, water adsorbed to clay -only used by microbes |
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guidelines for managing soil tilth (4) |
1) minimize tillage to reduce loss of aggregates
2) timing traffic activities to occur when: -soil is dry as possible -restricting tillage to period optimum soil moister conditions
3) mulching the soil surface with crop residues or plant litter to add OM
4) apply gypsum or other synthetic polymers |
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soil structural problems (3) |
soil crusting - happens after rainfall and has no structure
soil erosion - wind, water, and tillage
compaction |
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degradation of soil structure and consequences |
breakdown of weakened aggregates at soil surface
compacted subsoil - barrier to root growth and water
erosion carries away fine particles and OM is lost
surface crusting from rapid wet - dry
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Importance of soil structure (5) |
affects crop growth and yield by influencing
-storage of water and nutrients and their availability to crops - movement of water and nutrients in and through the soil during infilitration, draining, and leaching - aeration of roots and soil microbes - soils resistance to erosion by wind and water - soils resistance to compaction and crusting
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management practices |
continuous wheat vs grass
continuos cropping vs summer fallow
conservation tillage and continuous cropping for prairies
no till for corn in ON
direct drilling for cereals in PEI |
