----- Original Message -----
From: Liz Davis <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, August 30, 2002 5:28 AM
Subject: Rain/CEC
> We also experienced our first rain yesterday and last night. Heralding in
> the Spring. The drought seems to have made it a mild winter, with my
> dreaded willows only loosing their leaves for 5 weeks.
>
> I'm trying to get my head around CEC, if you add Ca2+, Mg2+, Na+, K+, you
> get the CEC. The remainder is what, hydrogen? Is this assumed, what
about
> aluminium?
> Any comments would be greatly appreciated.
>
> Hope many went to sleep to the sound of rain on the tin roof last night.
>
> L&L
> Liz
>
Hi Liz
No rain in the Riverina - we'll probably get a wet summer I suppose.
Re CEC - first -who did the test? - most fertiliser company tests dont
count hydrogen in the exchange complex, and in an acid soil this can
artificially inflate your calcium % by 20 or 30 % easy.
The Perry, Brookside, and Swep tests that I have all show hydrogen in
the raw numbers from the lab but if you're working with the jazzy graphs
that consultants provide for these same labs, most dont show it. You would
then assume most of whats missing is hydrogen but leave a little for
assorted other bases (usually up to 2% but sometimes as high as 6). A rule
of thumb is if your pH (in water) is in the ideal 6 to 6.2 then exchangeable
hydrogen is close around 12% of CEC - we need this little bit of acidity to
keep some chemical activity happening in the soil
Aluminium is everywhere in soil but its locked up as alumino-silicates
and exchangeable Al only becomes available when soils get very acid -
increasing rapidly as pH goes into low 5's (water) or under 4.5 (calcium
chloride test) - this seems to happen a little quicker and worse in grey
gravelly soils than in red soil - these low pH soils grow a diverse range of
aluminium tolerant plants - blakeleys red gum (snappy gum - brittle gum) -
ironbark - black cypress pine etc - but when we try to farm them its a
disaster - serradella and lupins do ok but most normal crop and pasture
species just can't hack it without serious help. There is usually also very
low organic carbon so holding added calcium in the profile is a problem too.
Hope maybe this helps
Cheers
Lloyd Charles
