I agree with some of the others in the use of Diesel and burning them out.. We had a few in a plot that we sawed off at ground level and left sit for a year or so.. We then took the tip of a chainsaw and ran it into the stump in several spots and down about 6 to 8 inches then saturated with diesel and set on fire.. It worked really well and I am able to run a disc thru it without worrying about the stumps..Before the removal we still disced the plot with a offset disc you just have to slow down and let it roll over the stumps easily..