21.
Spoor, G., Leeds-Harrison, P.B., 1999. Nature of Heavy Soils and Potential Drainage Problems [In:] Skaggs, R.W., van Schilfgaarde J. (Eds) Agricultural Drainage, Agronomy Monograph no. 38, American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, 677 S. Segoe Rd., Madison, Wisconsin USA.