CEC: npk..?

[Cor]

I read a lot of time that plants are able to utilise the bound fertiliser/nutrients in aquasoil.
But wich nutrients are those?
I know that by CEC it will pull out of the water any cations like Mg++, Ca++, K+ and that it exchanges magnesium, calcium, etc for hydrogen ions, so the KH and pH will drop.

But what I like to know is if nutrients like nitrate, phosphate and potash also will be bound into the aquasoil so that it will be available to the plant roots or water column.
TIA

 

[Nick potts]

For me, once the initial nutrients that were added to the soil when made have run out I treat it like any other inert substrate and just dose the water column to supply nutrients.

I am sure it binds some nutrients like no3 etc but I don't think enough to be useful, I think I read on here that soil only has so much space to store things and that space is quickly filled (i may have totally made that up lol)

@dw1305 will likely be able to explain the science better

 

[plantnoobdude]

negatively charged humic substances in soil will only attract cations. po4, no3 and such cannot bind to soil (as far as i am aware)
though, you can get some N in the form of ammonium which will bind to soil.

 

[Happi]

cation Charges such as NH4+ along with others are highly absorbed by the high CEC just like mentioned by the plantnoobdude
when the soil become exhausted, it become highly beneficial if you were to add NH4/Urea in the water.

 

[dw1305]

Hi all,

But which nutrients are those?
I know that by CEC it will pull out of the water any cations like Mg++, Ca++, K+ and that it exchanges magnesium, calcium, etc for hydrogen ions, so the KH and pH will drop.

But what I like to know is if nutrients like nitrate, phosphate and potash also will be bound into the aquasoil so that it will be available to the plant roots or water column.

Cation (and anion) exchange isn't <"entirely straightforward">. There are a <"number of factors in play">, the major ones being pH, valency and the relative abundance of ions.

Generally AEC is a much less strong effect than CEC, so soluble monovalent anions (like NO3-) are either in solution or lost, they don't tend to be bound to the AEC in the substrate.

This is the Lyotropic (Hofmeister) series for ions.

For anions the affinity is: SO4 = > NO3– > Cl– > HCO3– > OH– > F– and for cation the affinity is: Fe++(+) > Ca++ > Mg++ > K+ > Na+ > H+

Have a look at <"Can old Tropica soil......"> and linked threads for a bit more detail.

cheers Darrel