Fe conc. in Soils

Does DTPA-TEA method equally extract irons in both ferrous and ferric states? I thought it could explain the low Fe in Bf and Bhf of Podzol if DTPA-TEA method favors extracting ferrous states, assuming Fe in Podzolic B is predominantly in ferric state.

Hi Taku,
Good question. And yes, DTPA-TEA method does extract bot ferrous and ferric Fe forms, since both of them are plant-available forms.

OK. Thank you, Maja! I think I'm going to figure out something else...

But if the DTPA-TEA extracts both, low Fe in Podzol B cannot be explained like this.

I'm kind of looking at this by the opposite way. Fe in the Podzol B appears relatively low because most of other mineral soils have very high Fe. Crescent, Delta, Ladner soils are underlain by rocks containing a high concentration of sulfide minerals which most likely is composed of pyrite. The oxidation of pyrite increases Fe2+ in soil solution which is further oxidized to become Fe3+ both of which are extracted with DEPA-TEA, which can also explain why Gleysol in this area is so acidic in natural conditions.

But, also, I think Fe2+ and Fe3+ well-solubilized by DOM are lost from Podzol B by lateral seepage during the wet season. As for the Podzol Ap, I think some disturbances after the clearing of original forest increased Fe content.