Soil Aeration and Nutrients Flashcards
Processes controlling aeration
O2 enters soil through diffusion in rainwater
O2 stored in water and air pockets - bound or free
Good soils have high air
Impact of compaction
Lower oxygen availability as less pore space - oxygen taken up by solids and bound water
Many nutrients can only be taken up in presence of oxygen
Aerenchyma
Adaptation to thrive in low O2 conditions
Spongy tissues as modified cellulose structure
Large intercellular spaces w air channels for gas exchange
Pump oxygen into rhizosphere
Influence of soil texture
Sandy loam acts the same no matter the season - more oxygenated
Clay silt: decreasing aeration w soil depth - diff rates netween season (bad in winter)
Podzolisation (E horizon)
Ashy colour layer under soil below A horizon
Water driven transport component
Soil formation:
Dissolved org matter and ions form chelates which stick together
Moved w percolating water depper into soil
Inhibit microbe activity in top soil so build up of acidic surface layers and inhibits decomposition
No org matter in this horizon
Redeposition of org matter etc. in B horizon
Iron pans
Higher pH further down so Fe drops out of solution
Fe ions from ferrous to ferric and form rust
Exit solution and solidify
Hard for roots to push through
Impervious to water
Nutrient cycling
Biomass store: some in soil, most outside; enter soil through biological fixation and atmosphere, exit through death and waste
Inorg store: all in soil; enter through weathering and fertiliers, exit through leaching and gaseuous losses
Org store: most in soil, some out; enter following death, losses, mineralisation and immobilisation
Biological N fixation
Symbiosis w rhizobia
Signals to find each other - alkaloids from plant, nod factor from rhizobia
Initiate process
Plant detects nod factor and curls root hair and opens for rhizobia
Rhizobia enters and dividing cells infected - infection thread
Formation of root nodule w developed vascular system
Need little to no oxygen
