One thing to add to the above. It was posted that “The only way to judge crop height is to assess how much of the ground you can see through the crop. If you can clearly see the earth, the crop is still small. If you can only see the ground in the tractor wheelings, the crop is maybe 2 or 3 feet high. Once the crop covers the wheelings, you should expect a low wing aircraft to be damaged during the landing, but the pilots should be OK.”
There is another way. If the wind is significant, wheat and barley (and even long grass) show waves of windswept tops running across the field. If you can’t see them, the crop is short (or it is not windy). If you can, the crop is long enough to make at least some difference.
Regarding stock, avoid if possible.
Horses – the landowner will be really upset if they are expensive and/or in foal. You may thtink horses are expendabale compared with people, but the owner may not agree. I was told once that a prematurely dropped foal could cost £500,000. Dunno if that’s true.
One cow in a field is not a cow, it’s a bull. Avoid if at all possible. If not, once out of the aircraft, hide behind it until the bull seems unlikely to be interested in you.
A lot of cows in a field may include a bull. (Been there etc.) Avoid eye contact with the bull should you have to go into such a field. Cows sometimes change where they want to eat, and if you pick the empty side of a field to land in, they may suddenly move into it. Happened to a friend of mine. Ditto sheep – and that happened to me once. (We both just got away with it).
The crucial thing, as said by others, is to maximise safety of people, not the aircraft. (While glider field landings are normal, and usually uneventful, in the end it is still a piece of sporting equipment that can be mended or replaced. People not so easily.)
In extreme cases:
If the field is short, it is better to hit the far end slowly, having lost some energy, than hedge/wires etc. at the near end at flying speed.
If landing towards unavoidable trees, aim the nose between them and let the wings hit the trunks.
Hedges are not as soft as you might think. In July, a glider pilot had to choose between a groundloop or going into a hedge. He chose the latter, thinking it would cushion his arrest. Wrong – the nose of the glider hit a stem/trunk of one of the bushes, and resulted in really bad leg fractures. A ground loop to put a wing into it (if it even got that far) would have damaged the glider but probably avoided pilot injury (been there, too.)
(I have landed in a glider in over 100 fields, so write with a bit of experience, though not all apposite to power emergency landings.)
Chris N