ABSTRACT
Water and the Environment: Innovative Issues in Irrigation and Drainage. Edited by Luis S. Pereira and John W. Cowing. Published in 1998 by E & FN Spon. ISBN 0 419 23710 0
increased runoff, percolation, and sediment and pollutants losses [3] [4]. The quantity and quality of losses from drainage systems are related to the hydraulic layout considered. Subsurface drainage yields larger drainage volumes and greater losses of nitrates and soluble salts compared to surface drainage systems which are more connected with phosphorus and organic nitrogen losses. In the former, percolation is prevailing whereas in the latter run off is the main form of water flow [5] [6],
The effects of drainage on nutrients losses can be reduced with design and management suitable to specific site conditions and with the introduction of water table management practices such as controlled drainage and subirrigation. These practices, fairly new in Europe, were present in the U.S. since the begin of this century and have developed greatly in the last 20 years because of their environmental benefits [6]. In controlled drainage suitable devices allow flow of only the superficial water which may damage crops or limit machinery traffic. If subirrigation also occurs, water table depth is kept at a constant level throughout the year with the exception of periods when machinery access is needed. In this case, the water table is allowed to fall until field work is done.
