1. Loss of topsoil reduces crop yields;Adams;J. Soil Water Cons.,1949
2. Section 5: Environmental Assessment;Agriculture and Agri-Food Canada,1998
3. Agricultural Productivity in the United States;Ahearn,1998
4. Corn grain yield response to topsoil depth on deep loess soil;Alberts;Trans. ASAE,1987
5. Soil Factors Influencing Grape Production on Well-drained Lake Terrace Areas;Alderfer;Pennsylvania Agric. Exp. Stn. Bull.,1948