Nitrogen fixation by micro-organisms

If there is still a demand for nitrogen after mineral and organic nitrogen, as well as nitrogen from atmospheric deposition, has been taken up by the plant, nitrogen fixation can optionally take place (see switch N fixation). This uptake, N_Fix, is calculated by the function:

           (5.75)

where N_Demand is the original demand for nitrogen uptake, N_{Mineral→Plant} is the uptake of mineral nitrogen, N_{Organic→Plant} is the uptake of organic nitrogen, N_Atm→l is the uptake of nitrogen deposited on the plant leaves, and n_fix is a fixation uptake parameter. Nitrogen fixation, N_Fix, is added to the total plant nitrogen uptake, N_TotUpt.