http://www.borgford.com/ makes heavy duty root grapples. Years ago I came across them in Orange Talks.
He will size the grapple to your tractor, as other posters have mentioned , there is a tradeoff for implement weight (strength/durability and size) with the tractor payload and the front tires plys. I have a 5.5ft root grapple made of high strength alloy steel. A lof of borgford business is with the NW logging companies, where commerical use/abuse is the norm, so his implements are made for the task and to last. Where I live, I have lots of invasive root vines, rocky soil, and stone walls. The unit is designed to be insterted in the ground, and scoop up the entire mess, clamp it in the jaws and lift it out of the ground. After watching enough youtube videos of the less expensive root grapples and debris grapples getting twisted, bent, (and then unusable), I went with borgford bo-dozer root grapple.
http://www.borgford.com/BODOZER/grapple-rakes/ . The grapple is paired with a L5740, leaving enough payload of rock, brush, debris. The implement weight is approx 675 lbs.