Initialization of OrganicMatter

[Magnus Kamau Katana Lindhardt]

Hi DAISY community,

I am puzzled by the methods of initializing the Organic Matter (the organic matter in the soil and on the surface.)

In the file "dk-soil" it is set as follows:

(defcolumn Foulum default
  "Provided by DJF as part if the FertOrgaNic project."
  (Soil (MaxRootingDepth 100.00)
        (horizons (  -30.00 "Foulum AP")
                  (  -90.00 "Foulum B")
                  ( -150.00 "Foulum C")))
  (OrganicMatter original
                 (init (input 4411 [kg C/ha/y])
                 (end -18 [cm])
                 (root 911 [kg C/ha/y]))))

How are these values found? Are they empirical or modelled? 

Are there other ways of deriving OrganicMatter initialization parameters -- or is a warm-up period of 10 years sufficient?

[Per Abrahamsen]

Hi Magnus

Chapter 9.9 and Appendix 9.3 in the documentation describes SOM initialization in confusing details.

The numbers in dk--soil.dia are likely estimated with the "Carbon Balance" log.

However, I recommend ignoring the "OrganicMatter" parameter (leave it out), and instead combine 1) a short warmup period (one crop rotation, 2 years at minimum), and 2) an explicit partitioning of the SOM fractions of the Ap horizon with the "SOM_fractions" parameter.

(SOM_fractions 0.3 0.7) for a soil where the organic matter is fresh with a quick turnover and large mineralization, and (SOM_fractions 07.03) for a soil with older organic matter and less N release, or someone in between.  Use your plot with the lowest N input for calibration.

Kindly,

Per

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