Rape anything yellow is worth avoiding: turquoise
green before it goes yellow: rape stubble is almost as
bad looks ragged.
Ridge & Furrow (lots of it locally) will definitely wreck
your glider unless you are good enough to land along a
ridge few are !
Long crop see next slide
Anything not a uniform colour shade
gentle shading might be ok but not hard lines (->electric fences)
Ragged looking fields often grazing pasture or long
crop damaged by the wind, or rape
Livestock will eat your glider or trample on it
Also the landowner will not be happy if you frighten valuable