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Vuichard

-                      v25
+                      v26
 * '''Coefficient K_N_min'''. It corresponds to the [NH4+] (resp. [NO3-]) for which the Nuptake equals vmax/2. Kronzucker, 1995 reports values that range between 20 and 40 umol for NH4+ uptake. OCN seems to use 30 umol for both NH4+ and NO3-, because the value used in the code of OCN expressed in (gN m-2) is 0.84 (see [source:branches/orchidee-N/ORCHIDEE/src_stomate/stomate_soilcarbon.f90@19#L897 here]). In addition, in Kronzucker, 1995 and 1996, the concentrations are always expressed in umol. There is no clear reference about the standard volume it is related to. I assumed it is litter.
+* Conversion factor from (umol per litter) to (gN m-2) for K_N_min'''. I assumed conv_fac_concent equals to 14 * 1e3 * 1e-6 * 2 with
+  - 14   : molar mass for N (gN mol-1)
+  - 10^3 : conversion factor (dm3 to m3)
+  - 10-6 : conversion factor (ug to g)
+  - 2    : m3 per m2 of soil
+ I wonder why it assumes 2 m3 per m2 of soil. The depth of the soil is 2 meter but it doesn't mean that all the column contains only water, there is also soil, no ? The question is : what is the volume that is considered for the concentration of NH4+ and NO3-. Is it a volume of soil or of solution ? If it is a volume of solution, I would suggest to multiply by a factor corresponding to the relative volume of water within the soil (like soilhum). Not done yet.