An experimental field was constructed on a heavy clay soil at the northeast Delta (Dakhlia Governorate) to study the effect of different tile drain spacings on watertable recession and some physical and chemical properties of heavy clay soil. The experimental field was provided by tile drainage system with three drain spacing treatments (15, 30 and 60 m) at fixed depth of 1.5 m.
The results indicated that by the end of the irrigation interval (after three weeks), the watertable level went deeper to reach 131, 103 and 94 cm soil depth for 15, 30 and 60 m tile drain spacing treatment, respectively. The average watertable drawdown rate through an irrigation interval was 6.24, 4.90 and 4.48 cm/day for the corresponding treatments. The watertable drawdown ratio (ht/Ho) decreased as the tile drain spacing became wider. It was 0.87, 0.69 and 0.63 after three week for the corresponding treatments. The soil moisture content increased as tile drain spacing increased. It increased by 16 and 26% in surface layer and by 18 and 30% in subsurface layer under 30 and 60 m tile drain spacing, respectively compared to the narrow one. Soil bulk density increased as tile drain spacing increased. It increased by 4 and 11 % in surface layer and by 3 and 9% in subsurface layer under 30 and 60 m tile drain spacing, respectively compared to the narrow one. Total soil porosity decreased as tile drain spacing increased. It decreased by 3 and 9 % in surface layer and by 3 and 8% in subsurface layer under 30 and 60 m tile drain spacing, respectively compared to the narrow one. Tile drain spacing treatments realized a postive effect on soil salinity. The reduction in soil salinity followed the order of: 15> 30> 60 m tile drain spacing. The soil salinity was reduced by 13 and 41 % in surface layer and by 26 and 39 % in the subsurface layer under 30 and 60 m tile drain spacing, respectively compared to the narrow one. The reduction in soil sodicity followed the order of: 15> 30> 60 m tile drain spacing. The soil sodicity reduced by 13 and 46 % in surface layer and by 24 and 46 % in the subsurface layer under 30 and 60 m tile drain spacing, respectively compared to the narrow one.
Tile drain spacing treatments realized an enhancing effect which progressively as time proceeded by lowering the water table and accelerated its recession, particularly under narrow spacing traetment. However, treatment of 30 m drain spacing gave satisfactory results by lowering watertable and reducing salinity and alkalinity with improving soil physical properties. It is also reduce drainage costs. Also, tile drainage spacing treatments promoted a favourable conditions by decreasing soil salinity and sodicity and creating a suitable soil moisture content which plays an important role in improving soil moisture-aeration status in the root zone.