Upper boundary condition

Salts that infiltrate the soil can come from several sources. Salt deposited from the atmosphere enters the soil profile with the infiltrating water from precipitation, (q_in – i_ar). A road salt application can optionally be chosen (see switch RoadSaltApplication). In this case an additional salt input, q_Clroad, is added to the total infiltration during conditions when the air temperature is within a specified range determined by the parameters t_salthigh and t_saltlow. Alternatively, salt can be added to a storage pool on the road (see switch SaltRoadStorage), which emits salt resulting in a salt infiltration rate, q_ClRoadInf, as described in detail below. Finally, water used for irrigation of crops (see Irrigation below) may also contain salts. The total salt infiltration is calculated as:

(2.56)

where c_Cldep is the salt deposition concentration, q_in is the total amount of infiltrated water, i_rate is the irrigation rate, i_driprate is the irrigation rate for drip irrigation and c_Clirrig is the concentration of salts in the irrigation water, which can either be given as a parameter or can be read from a PG-file (see switch IrrigConcInput).

Secondly, salts are removed from the surface through surface runoff, q_surf, according to:

                                                       (2.57)

where q_Clroff is the removal rate of salts with runoff and C_Clz1 is the salt concentration in the uppermost soil layer.