This pane is on the MODFLOW Features tab of the Object Properties dialog box.
If MULTIPLE_LAND_USE_PER_CELL is specified, then it is required to specify LAND_USE_AREA_FRACTION which identifies the model cell location for each land use and the area it occupies. If the sum of all the crop fractions for a cell exceeds 1, then the crop fraction for hat cell are scaled to equal 1. If the sum of all the crop fractions are less than 1, then the undefined area is set to bare soil.
If SINGLE_LAND_USE_PER_CELL is specified, then LAND_USE_AREA_FRACTION is optional and specifies the area that the land use covers and the rest is considered bare/fallow land.If not specified, then where ever LOCATION has a crop identified (>0) uses 1.0 as the fraction (crop occupies entire cell).