Nitrification processes

The nitrification rate i.e. the flow of nitrogen from the soil ammonium pool to the soil nitrate pool, N_NH4→NO3, can be calculated in two different ways, either by accounting for microbials or without microbials (see switch Nitrification). In the simplified approach the nitrification is calculated as:

                                 (6.54)

where n_pH is a parameter accounting for pH.

The switch Nitrific temp response determines the temperature response, f(T) and the response function for soil moisture, f(θ), is the common soil moisture response. These response functions are described in the section Common abiotic functions.

The soil ammonium and nitrate content also affect nitrification. This response function is calculated as:

                              (6.55)

 

 

where r_nitr,amm and n_rate are parameters. See viewing function Nitrification rate under optimal moisture and temperature conditions.

If microbials are accounted for, eq.(6.54) is modified into:

                          (6.56)

where n_micrate is a nitrification rate coefficient and N_micrN is the biomass of the microbial nitrifiers. The nitrogen in the microbial biomass in not included in the overall nitrogen balance of the soil due to its low nitrogen concentration.

The response function for soil ammonium concentration, f(N_NH4Cons), is calculated as:

                                   (6.57)

 

 

where n_hrateNH4 is the nitrification half rate for ammonium concentration. See viewing function Nitrification response function for ammonium content.

Microbial biomass of nitrifiers is a function of their death, growth and respiration rates:

                                     (6.58)

Microbial growth rate is calculated as:

            (6.59)

where n_nitrgrow is a growth coefficient for the nitrifiers.

The response function for dissolved organic carbon concentration, f(C_DO,nCons), is calculated as:

                                                                      (6.60)

 

where n_hrateDOC is the half rate for dissolved organic carbon. See viewing function Nitrification response function for dissolved organics.

The response function for soil nitrate concentration, f(N_NO3,nCons), is calculated as:

                                   (6.61)

 

 

where n_hrateNO3 is the half rate for nitrate concentration. See viewing function Nitrification response function for nitrate content.

Microbial death rate is calculated as:

                                                                               (6.62)

where n_nitrdie is a death coefficient for the nitrifiers.

Finally, microbial respiration rate is calculated as:

                             (6.63)

 

where cn_m is the carbon nitrogen ratio of the decomposing micro-organisms.