## 2.18.7. Calculation of N uptake streams from active uptake and fixation[¶](#calculation-of-n-uptake-streams-from-active-uptake-and-fixation "Permalink to this headline")
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Once the final \\(C\_{nuptake}\\) is known, the fluxes of C to the individual pools can be derived as

> \\\[C\_{nuptake,x} = C\_{frac,x}.C\_{nuptake}\\\]
> 
> \\\[N\_{uptake,x} = \\frac{C\_{nuptake}}{N\_{cost}}\\\]

Following this, we determine whether the extraction estimates exceed the pool size for each source of N. Where \\(N\_{active,no3} + N\_{nonmyc,no3} > N\_{avail,no3}\\), we calculate the unmet uptake, \\(N\_{unmet,no3}\\)

> \\\[N\_{unmet,no3} = N\_{active,no3} + N\_{nonmyc,no3} - N\_{avail,no3}\\\]

then modify both fluxes to account

> \\\[N\_{active,no3} = N\_{active,no3} + N\_{unmet,no3}.\\frac{N\_{active,no3}}{N\_{active,no3}+N\_{nonmyc,no3}}\\\]
> 
> \\\[N\_{nonmyc,no3} = N\_{nonmyc,no3} + N\_{unmet,no3}.\\frac{N\_{nonmyc,no3}}{N\_{active,no3}+N\_{nonmyc,no3}}\\\]

and similarly, for NH4, where \\(N\_{active,nh4} + N\_{nonmyc,nh4} > N\_{avail,nh4}\\), we calculate the unmet uptake, \\(N\_{unmet,no3}\\)

> \\\[N\_{unmet,nh4} = N\_{active,nh4} + N\_{nonmyc,nh4} - N\_{avail,nh4}\\\]

then modify both fluxes to account

> \\\[N\_{active,nh4} = N\_{active,nh4} + N\_{unmet,nh4}.\\frac{N\_{active,nh4}}{N\_{active,nh4}+N\_{nonmyc,nh4}}\\\]
> 
> \\\[N\_{nonmyc,nh4} = N\_{nonmyc,nh4} + N\_{unmet,nh4}.\\frac{N\_{nonmyc,nh4}}{N\_{active,nh4}+N\_{nonmyc,nh4}}\\\]

and then update the C spent to account for hte new lower N acquisition in that layer/pool.

> \\\[\\begin{split}C\_{active,nh4} = N\_{active,nh4}.N\_{cost,active,nh4}\\\\ C\_{active,no3} = N\_{active,no3}.N\_{cost,active,no3}\\\\ C\_{nonmyc,no3} = N\_{nonmyc,no3}.N\_{cost,nonmyc,no3}\\\\ C\_{nonmyc,no3} = N\_{nonmyc,no3}.N\_{cost,nonmyc,no3}\\\\\\end{split}\\\]

Following this, we determine how much carbon is accounted for for each soil layer.

> \\\[C\_{accounted,x,j} = C\_{spent,j,x} - (N\_{acquired,j,x}.CN\_{plant}.(1.0+ gr\_{frac}))\\\]