This function calculates the indicator for the the Magnesium content of the soil by using the Mg-availability calculated by calc_magnesium_availability
ind_magnesium(D_MG, B_LU_BRP, B_SOILTYPE_AGR)
(numeric) The value of Mg calculated by calc_magnesium_availability
(numeric) The crop code (gewascode) from the BRP
(character) The type of soil
The evaluated score for the soil function to supply magnesium for crop uptake. A numeric value.