The blades will break the straw and kill cover crop grasses that have flowered.  If the main crop is planted into a cover crop of standing rye or some other type of grass.  The roller crimper can be used when soybeans are still less than 6 inches tall.  The grass will be killed and the soybeans will survive and grow up through the mat of cover crop.  The roller crimper can be filled with water to adjust the weight depending on soil