Chapter 4, pp. 111-159 in: Taylor, N.L. (Editor). Clover Science and Technology. No. 25 in the series Agronomy. American Society of Agronomy, Inc., Crop Science Society of America, Inc., Soil Science Society of America, Inc., Publishers, Madison, Wisconisin, 53711, U.S.A. AD U.S.Regional Pasture Research Laboratory, ARS-USDA, University Park, Pennsylvania.