These have been planted in a couple of fields around here the past two years years. They grow just a few inches underground but 12-18 inches above ground and big around as your arm. I thought they were some type of animal feed because there is a big dairy farm down the road but both years they were left in the field, and I'm talking about 40-50 acre fields, until cold weather completely kills them and then disked under. Must be something to enrich the soil but I wondered what they are since I had never seen them before.