Coulters come in a wide variety of sizes and shapes. The right coulter for your application depends on your soil composition and humidity as well as the crop you're planting, the residue from your last crop and your choice of farming techniques. Plain coulters provide excellent penetration and cutting ability with very little soil disturbance while wavy coulters disturb the soil to a much greater degree. Of course, the depth of the wave has a lot to do with how much the soil is disturbed. Fluted coulters are somewhere in between.