I noticed something interesting this week. I was visiting a field in Dillon where Gordon Mikell with NRCS dug a soil pit last month (What Lies Beneath The Soil). Once Gordon was finished with the pit, it was filled in and the area around it was disked to level the ground back out. This was the first time in 4 years any part of this field has been disked. Take a good look at the two photos below.
How about that pigweed in the disked area? This field has had a continuous cash crop and cover crop rotation for 3 years now. There’s no pigweed to be found in the rest of the field. Does that mean there’s no pigweed seed in the field? I would bet there is.
What I believe is happening here is for the last 3 years, the cover crop residue has suppressed pigweed and kept a number of seeds from germinating. Once a portion of the field was disked, the residue was turned under and the conditions were finally right for the pigweed seed to germinate. It seems pigweed doesn’t compete well with a cover crop until the residue is removed or the soil is disturbed. Unfortunately, the cover crop doesn’t seem to have the same effect on horseweed.
That’s my theory.