### 2.18.2.4. Cost of Active Uptake[¶](#cost-of-active-uptake "Permalink to this headline")

The cost of N uptake from soil, for each layer \\(j\\), is controlled by two uptake parameters that pertain respectively to the relationship between soil N content and N uptake, and root C density and N uptake.

For non-mycorrhizal uptake:

> \\\[N\_{cost,nonmyc,j} = \\frac{k\_{n,nonmyc}}{N\_{smin,j}} + \\frac{k\_{c,nonmyc}}{c\_{root,j}}\\\]

and for active uptake:

> \\\[N\_{cost,active,j} = \\frac{k\_{n,active}}{N\_{smin,j}} + \\frac{k\_{c,active}}{c\_{root,j}}\\\]

where \\(k\_{n,active}\\) varies according to whether we are considering ecto or arbuscular mycorrhizal uptake.

> (2.18.1)[¶](#equation-18-2 "Permalink to this equation")\\\[\\begin{split}k\_{n,active} = \\left\\{\\begin{array}{lr} k\_{n,Eactive}& e = 1\\\\ k\_{n,Aactive}& e = 0 \\end{array}\\right\\}\\end{split}\\\]

where m=1 pertains to the fraction of the PFT that is ecotmycorrhizal, as opposed to arbuscular mycorrhizal.

