baymule
Garden Master
Jim, digging by hand-when you get to the rock hard soil, fill it with water and come back in a day or two to finish digging it out. Here are a couple of links that might help you out.
http://coststudies.ucdavis.edu/files/98pecans.pdf
http://aggie-horticulture.tamu.edu/fruit-nut/files/2010/10/improved-pecans.pdf
http://coststudies.ucdavis.edu/files/98pecans.pdf
http://aggie-horticulture.tamu.edu/fruit-nut/files/2010/10/improved-pecans.pdf