This function calculates the indicator for the the S-index by using the SLV calculated by calc_slv
ind_sulfur(D_SLV, B_LU_BRP, B_SOILTYPE_AGR, B_AER_CBS)
(numeric) The value of SLV calculated by calc_slv
(numeric) The crop code (gewascode) from the BRP
(character) The type of soil
(character) The agricultural economic region in the Netherlands (CBS, 2016)
The evaluated score for the soil function to supply sulfur for crop uptake. A numeric value between 0 and 1.