### 2.18.4.1. Free Retranslocation[¶](#free-retranslocation "Permalink to this headline")

Some part of the leaf Nitrogen pool is removed without the need for an C expenditure. This ‘free’ N uptake amount, (\\(N\_{retrans,free}\\), gN m\-2) is calculated as

> \\\[N\_{retrans,free} = max(N\_{fallingleaf} - (C\_{fallingleaf}/CN\_{litter,min} ),0.0)\\\]

where \\(CN\_{litter,min}\\) is the minimum C:N ratio of the falling litter (currently set to 1.5 x the target C:N ratio).

The new \\(N\_{fallingleaf}\\) (gN m\-2) is then determined as

> \\\[N\_{fallingleaf} = N\_{fallingleaf} - N\_{retrans,free}\\\]

and the new litter C:N ratio as

> \\\[CN\_{fallingleaf}=C\_{fallingleaf}/N\_{fallingleaf}\\\]

