From: London, Surrey, United Kingdom
Croplands are something that transition from one state to another so in the spring they are not the same as they are in late summer or fall. The game could do a better job of modeling this for scenarios that last several months.
The primary impact of cropland is that it adds +1 for most movement types. From experience, any time of year moving across cropland is heavy going on foot, and probably worse in a wheeled vehicle, as even if there are no crops currently in place the soil is usually extremely lumpy where it's been ploughed earlier in the year. Better to be going over grazing land, which would just be "open".
Anyway, it's at the designer's discretion: if you don't think the farmland is going to be a barrier to movement, keep it as "open".
"What did you read at university?"
"War? Huh. What is it good for?"