Out here in the west (read "stinkin' desert") many "plowed fields" are crop circles, and while the sprinkler system is a hazard, at least it is visible. What will get your attention are the deep circular ruts left by said sprinkler system. That and the (often) circular furrows, although many farmers ("Agrarians," as Pez D. Spencer calls them) plow in parallel lines and let the sprinkler deal with making its own path. What can be annoying, if not downright dangerous, is having to land with the furrows, as opposed to at an angle, no matter what the crosswind component may be. Some crops need very deep furrows, and landing across the pattern is going to be extremely rough and potentially dangerous.

So far, in 20 years of sailplane XC and over 1,200 flights, I have "landed out" less than 10 times, and all but one were on a runway. Some were dirt, but they were all "real" runways. The only one that wasn't USED to be a runway, but it had degraded into just a rough dirt line in the weeds.