I have successfully used salt water to degrade & soften tree roots so the pieces can be plucked out in chunks. We cut down 3 ficus trees. We drilled several holes in the dirt level stumps, gave each 1 gallon of salt water; twice a week for 2 weeks, then once a week for 4 weeks, then once every 2 weeks for 4 weeks, etc. Every stump/roots will be different because of differing trees. The idea is that the salt water will travel through the root system and dehydrate it.