Abstract: A machine for turning material piled on the ground in a windrow comprises first and second track assemblies spaced apart from one another and having a lift assembly therebetween. The lift assembly lifts the material upwardly and deposits it to the rear. The first and second track assemblies are individually driven so as to eliminate bending forces on the intermediate lifting assembly. Extensible belt tensioners are provided for tensioning the belt, and these extensible belt tensioners are protected from the material being elevated and aerated. The method involves moving the belt assembly along a first pit containing the material to be composted and then reversing the belt assembly for returning in the opposite direction along an adjacent pit containing materials.