A cultivator adapted to straddle a windrow of material such as compost. A frame has an improved disintegrator and aerator comprising a horizontal drum crosswise of the windrow with a plurality of cultivator blades disposed in two helical arrays between opposite ends of the drum, the arrays being circumferentially spaced 180.degree. apart about the drum and extending equal distances on opposite sides of a central, longitudinal, vertical plane along the center of the frame. The blades on the right and left sides of the drum have paddle portions at their ends transversely offset toward the central vertical plane and contoured to move material sidewise and heap it up into a peak along the center of the windrow. The helical arrays of blades are identical and symmetrical on opposite sides of the windrow center, enabling repeated passes of the cultivator to circulate material between the inside and the outside of the windrow while maintaining it with a triangular cross-section of ever-increasing height and ever-diminishing base width for improved chimney effect and aerobic heat utilization within the windrow. Two specific blade shapes are shown, one primarily for windrow cultivation and aeration, and another for shredding paper, cardboard, magazines, and the like prior to composting. A modified form of rotor is disclosed, for agricultural use, to form parallel ridges and furrows in a ground surface to prepare it for planting and subsequent irrigation.