Recent pictures of our Kentucky Wonder pole bean bed grown in very depleted soil . The major difference was that one side got a very thin layer of compost and alfalfa meal and the other side did not.
Thanks to the beans nitrogen fixing capability no major difference in bean production was noticed. The unfertilized/uncomposted side (left side, top picture) appears to have a little less plant growth due to one of the hoops not having vines. The back side (bottom picture) is a different story....both sides of the bed (left side-fertilized and right side-unfertilized) have equal amounts of green growth on the hoops.
The take home message is that when soil appears to be depleted of nitrogen (yellow stunted plants or low N confirmed by soil test), legumes are a good choice. (Thank you Tom Liggett for this great demonstration idea!)