The "Buffer" in the SOM submodel

[Su-Yi]

Hello everybody,
I am a user of daisy from Germany and very happy to have the chance of
open discussion on this website:)

Recently I’m struggling with the structure of the soil organic matter
submodel in Daisy. As my understanding, SOM, SMB and AOM pools are the
three main compartments of organic matter pools in Daisy. But when I
read Daisy program reference manual (Abrahamsen, 2006), I found
“Buffer” pool was also included in this submodel. In the manual (page
418), there is a short description of “Buffer”: it mentions that
“Buffer” is the buffer between AOM pools and SOM, but so far I still
couldn’t get it.

Therefore, I need your kind help to know what the complete concept of
“Buffer” in Daisy is and it would be very nice if you could give me
the background references about the idea of including “Buffer” pool in
the soil organic matter submodel.

Thank you very very much!!!

[Per Abrahamsen]

Hi Su-Yi.

The organic fertilizers are normally divided into a slow pool (AOM1)
and a fast pool (AOM2), both which are being eaten by the soil
microbiomess (SMB) before eventually being turned into soil organic
matter (SOM).

If the fertilizer has been stored for a while, some of it may already
have been digested by microbes, and thus be indistinguishable from the
soil organic matter. We represent this by adding a third pool
(AOM3), the content of which goes to the
soil organic pools without the intervention of the soil microbes.

The "buffer" controls this process, it decides which SOM pool this
already processed matter should go to, and how fast. With the current
parameterizations, the answers are always "SOM2" and "instantly".

Regards,

Per A.

[Su-Yi]

Hello Per A.,

Thanks a lot for your quick response and nice explanation.

Concerning the role of “Buffer” in the process which you mentioned,
can I say “Buffer” is an intermediate status (or pool??) before added
organic matter (AOM3) being turned into soil organic matter (SOM2)?

Besides, I have two more technical problems:
1. If I want to assign part of organic fertilizers (plant residues) as
AOM3 in Daisy, how can I do? By changing which part of code?
2. How can I define the size of “Buffer”?
For example, if I have the AOM pools as follows:

(om ((C_per_N 90 [(g C/cm^3)/(g N/cm^3)])
(efficiency 0.5 0.5 [])
(fractions 0 0.8 0.2 [])
(initial_fraction 0.8 [])
(turnover_rate 0.0002 [h^-1]))
((efficiency 0.5 0.5 [])
(fractions 0 1 0 [])
(turnover_rate 0.002 [h^-1])))

Can I say 80% of AOM1 is going to SMB2 pool and 20% of AOM1 is going
to SOM buffer?



Best regards,
Su-Yi

[Per Abrahamsen]

> Concerning the role of "Buffer" in the process which you mentioned,
> can I say "Buffer" is an intermediate status (or pool??) before added
> organic matter (AOM3) being turned into soil organic matter (SOM2)?

Yes.

> Besides, I have two more technical problems:
> 1. If I want to assign part of organic fertilizers (plant residues) as
> AOM3 in Daisy, how can I do? By changing which part of code?

Are you talking about residues from the crop growing on the field, or
plant residues applied as organic fertilizer?

For the applied fertilizer, see the "slurry" parameterization in
"fertilizer.dai".

For the crop, see for example the file "grass.dai", where the om pools
are defined individually for each part of the crop.

The "slurry" definition assigns 10% of the fertilizer to AOM3, because
the "initial_fraction" parameters for AOM1 and AOM2 sums up to 90%.

> 2. How can I define the size of "Buffer"?
> For example, if I have the AOM pools as follows:
>
> (om ((C_per_N 90 [(g C/cm^3)/(g N/cm^3)])
> (efficiency 0.5 0.5 [])
> (fractions 0 0.8 0.2 [])
> (initial_fraction 0.8 [])
> (turnover_rate 0.0002 [h^-1]))
> ((efficiency 0.5 0.5 [])
> (fractions 0 1 0 [])
> (turnover_rate 0.002 [h^-1])))
>
> Can I say 80% of AOM1 is going to SMB2 pool and 20% of AOM1 is going
> to SOM buffer?

That is correct.

[Su-Yi]

Thanks a lot for the advice!!!