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Resource: used or used up in processesIron oxides
Appears in 22 processs and 45 steps. Everything below is linked: open a process to see it in context.
Top processes
- Mineral surface area sets binding sites: smectite about 600-800 m2/g, ferrihydrite 200-700, kaolinite 5-20
- In acidic humid soils reactive Fe and Al phases (short-range-order oxides, Al-humus complexes) dominate retention by ligand exchange, and radiocarbon turnover times correlate with their content
- Root exudates such as oxalic acid dissolve Fe-bound carbon: in experiments oxalic acid released mineral-bound carbon and raised microbial decomposition
- and 2 more in this process
Soil gas exchange and redox
3 steps- Phosphate displaces OH and OH2 on goethite, gibbsite and allophane surfaces, forming inner-sphere complexes
- Sorption capacity scales with oxalate-extractable Al + Fe, and saturation degree is phosphate divided by 0.5 times (Al + Fe)
- Slow solid-state diffusion into oxide micropores over days to years converts labile to occluded phosphate
Show 16 more processes
- Released Al and Si precipitate as allophane, imogolite and ferrihydrite instead of crystalline clay
- Strong phosphate retention (andic criteria: oxalate Al + half Fe at least 2%, bulk density 0.9 g/cm3 or less, P retention at least 85%) fixes phosphorus
- In wet climates over millennia allophane crystallises to halloysite and Fe oxides and the carbon protection weakens
- Phytate (inositol hexakisphosphate) is the main identified organic P but sorbs strongly to Fe and Al oxides and clay, limiting access
- Roots and microbes exude citrate, malate and oxalate and extrude H+ to desorb phosphate from Fe and Al oxides and dissolve Ca phosphates
- Released phosphate is re-adsorbed to Fe and Al oxides within minutes to hours, so uptake must compete with fast sorption
Soil sulfur cycling
1 stepOften found with
Iron oxides 22Clay minerals 13Phosphate 13Aluminum oxides 9Clay minerals 8Iron-reducing bacteria 8Carbon 7Plant roots 7Iron 6Aluminum 6Mineral surfaces 6Oxygen 5
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