I remember the original article - I think the photos were shot in Warwickshire or Worcestershire. This was relevant because the timings they gave for each crop don't work across the country - certainly different in E Anglia, and fields of the same crop didn't look the same locally. Flying from gliding sites in other parts of the country always requires me to make a mental adjustment, because even, say, wheat looks different in the Cotswolds from in Cambridgeshire- field size makes a surprising difference to the overall appearance.
Pictures are a good start, but no substitute for actually inspecting crops from the air and then on the ground. The fields next to the runway will usually have different crops each year, so if you look at them before entering the circuit, and then after landing, you can build up a good mental library.