This pane is on the MODFLOW Features tab of the Object Properties dialog box.
ADDED_DEMAND specifies any additional demands to include with the crop demand. ADDED_DEMAND only applies to irrigated crops and the additional demanded water only becomes surface runoff or deep percolation based on the fraction specified in the WBS Block "ADDED_DEMAND_RUNOFF_SPLIT"
The added demand is summed with other added demands (e.g. WBS Block ADDED_CROP_DEMAND FLUX and ADDED_CROP_DEMAND RATE.)
