\begin{equation}
\mathit{h_{nitrogen}}=\sum_{l=1}^\mathit{nbdl} \left(\mathit{soil\_hum\_month} \cdot \mathit{rpc} \cdot \left(e^{-{\frac{\mathit{z_{soil}}\left(l-1\right)}{\mathit{z_{nitrogen}}}}}-e^{-{\frac{\mathit{z_{soil}}(l)}{\mathit{z_{nitrogen}}}}}\right)\right)
\end{equation}
