Here are a couple of pictures from Eric Van Ginkel, who works for the Iowa Cubs. He also works on several other sports fields in the Des Moines area.
This was a field that had highly compacted soil following construction. They sodded it last fall with Kentucky bluegrass, but the sod had shallow roots and grew slowly because of the compaction. This spring, they deep-tined the area with solid tines. The area improved. They recently used hollow tines on the deep-tine unit to pull cores. These pictures show the rooting into the holes from the solid tines in the spring in cores that were removed this fall.
This is something that I have observed as well on area that have been deep-tined with solid tines. It is amazing how much root growth can occur in these aerification holes. We will need to do a follow up in the spring and see how much rooting there is into the holes left by the hollow tines.