This function calculates the fraction present in the crop rotation
calc_rotation_fraction(ID, B_LU_BRP, crop)
The fraction of specific crop types within the crop rotation sequence. A numeric value.
This function calculates the fraction present in the crop rotation for specific crop categories. These categories include "starch", "potato", "sugarbeet", "grass", "mais", "alfalfa","catchcrop","cereal","clover",'nature', rapeseed',"other","rustgewas",and "rustgewasdiep".