"Cropland ... Includes: All land from which crops were harvested or hay was cut. All land in orchards, citrus groves, vineyards and nursery and greenhouse crops. Land in rotational pasture and grazing land that could have been used for crops without additional improvements. Land used for cover crops, legumes, and soil improvement grasses, but not harvested and not pastured. Land on which crops failed. Land in cultivated summer fallow."
By definition cropland is where you could grow crops, the rest is grassland.
I think "grazing land that could have been used for crops without additional improvements" (emphasis mine) doesn't include e.g. established pasture which could be easily but not trivially used as cropland, right? I would have assumed it was a catch-all for dual purpose crops etc.
https://www.fao.org/3/Y4171E/Y4171E20.htm#p4990_295868
"Cropland ... Includes: All land from which crops were harvested or hay was cut. All land in orchards, citrus groves, vineyards and nursery and greenhouse crops. Land in rotational pasture and grazing land that could have been used for crops without additional improvements. Land used for cover crops, legumes, and soil improvement grasses, but not harvested and not pastured. Land on which crops failed. Land in cultivated summer fallow."
By definition cropland is where you could grow crops, the rest is grassland.