Crop residues (such as rice straw and corn stover) are potential feedstocks for cellulose ethanol production. Because of their relative abundance in many parts of the world, many countries are considering the use of crop residues as bioenergy feedstocks. However, studies by Ann Kennedy (a soil scientist from the USDA-Agricultural Research Service and adjunct professor at Washington State University) indicate that the conversion of crop residues into cellulose ethanol “may not be a good idea for farmers growing crops without irrigation” and in areas where annual precipitation is less than 25 inches. For long term health effect of the soil, Professor Kennedy recommends leaving some of the crop residue on the soil surface. In so doing, it will “stay around longer”, and microorganisms will slowly convert it to organic matter. Tillage may cause an overmixing of the residue with soil. This would cause the residue to be consumed too quickly, resulting in its conversion and release into carbon dioxide (instead of conversion to organic matter). If the residue were harvested and utilized for other purposes, “soil fertility would drop and farmers would have to find other ways to increase the amount of organic matter in their soils”..