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Field experiments were conducted for two years in the Western Delta of Egypt to investigate the effects of controlled drainage on the quality of subsurface drainage outflows. Two water table management methods were applied in the 2.54 ha experimental field: free conventional subsurface drainage and controlled drainage. Controlled drainage was applied at 60 cm. depth during both seasons. Drain discharge volumes and nitrate-N and orthophosphate-phosphorus concentrations were monitored during the growing seasons. The controlled drainage (CD) treatment significantly reduced the total drainage outflow by 68% during the summer season and by 28% during the winter of 1999-2000 at 99% confidence level, compared to free conventional drainage (FD) treatment. The CD also reduced the total nitrate-N in drainage water by 73%, and 32% during the summer and the winter seasons respectively, compared to the FD treatment.

The CD treatment reduced the total orthophosphate-phosphorus losses by 77% during summer of 1999 and by 30% during winter of 1999-2000 compared to the FD treatment; however, in general the total mass loss was low in both treatments. The results of the experiment showed the potential environmental and economic benefits with the application of controlled drainage in semi-arid regions. Copyright (C) 2001 John Wiley & Sons, Ltd.