Many materials can be incorporated into clay soil to increase its potential. Your local agricultural extension service may be of invaluable help, as they can offer a soil test to get you started. Once you have the results in hand, sand, wood chips and cover crops can be grown to improve the production capacity of any clay material. Of course, this requires time and a couple of growing seasons for best results.
Follow the soil test results from the extension service. The end goal for amending clay soil is to improve the soil's porosity, permeability and drainage. Bulk items such as wood chips, straw and sand must be worked into the soil.
Use the rototiller to break up as much of the surface of the clay soil as you can. You may have to add water to the ground prior to tilling. Allow the soil to soak up as much water as possible, but not too much where you are making mud instead of breaking the surface.
Place 2 to 3 inches of sand over the area, and rototill the sand into the soil. This task will take many passes from the rototiller. The deeper you can work the sand into the clay, the more porosity the soil will have.
Add approximately 2 inches of wood chips or decomposed wood chips on top of the clay soil incorporated with the sand, then rototill into the mix. Again, this may take a few passes with the rototiller to get the wood chips worked into the soil.
Layer the surface approximately 6 inches deep with straw. The straw will keep the surface of the new soil from crusting over due to any hard rains and moisture.
Plant cover crop seed into the layer of straw and water well with the sprinkler attachment on the end of the garden hose. Some varieties that do well in poor soils are white and red clover, annual ryegrass and some legumes. Follow the recommendations, if any, of the extension service for the cover crop seed.
Allow the cover crop to grow for one full season. The straw layer will break down as the cover crop matures. Rototill all of the material into the clay. Replant with a new cover crop for the winter season. By spring, the clay soil will be full of organic material and ready for a productive life.