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-                      v52
+                      v53
 > B. Guenet [[BR]]
+> From what I understood NH4+ in OCN is in kg N ha-1 which make sense with Zhang et al., 2000. The Li et al 1992 equation confuse me a bit because from what I understood from the equations NH4 is in gN kg soil; but solid soil, it means that we can easily convert it as a stock, but in the description it is per kg of liquid soil...
 . '''Ammonium adsorption''' (2). Li et al. (1992) defines FIXNH4 as the proportion of adsorbed NH4+. One may assume that consequently the NH4+ that is not adsorbed is NH4+ x (1-FIXNH4) and that we want to consider this quantity for possible nitrification, transformation to ammonia, .... But in OCN, we do not multiply the state variable (SV) representing NH4+ by (1-FixNH4) but by (1-FixNH4/(1+FixNH4)) (see, [source:branches/orchidee-N/ORCHIDEE/src_stomate/stomate_soilcarbon.f90@19#L746 here]). This tends to assume that FixNH4 represents the ratio adsorped NH4+ to non-adsorped because FixNH4/(1+FixNH4) = (NH4adsorp/NH4non_adsorp)/((NH4non_adsorp+NH4adsorp)/NH4_non_adsorp) = NH4adsorp / NH4tot. This needs to be clarified ...