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Materials and Methods

Materials & Methods -  In the first stage of these studies, the saturated hydraulic conductivity was measured in the field by auger hole method (Van Bear, 1958). The saturated hydraulic conductivity is one of the most important soil properties It is an important physical parameter for designing drainage system. It is play an essential role for water flow in soil. In general, the average hydraulic conductivity, Ksat, is 6.69 cm/day. Generally, according to Missland and Haskea (1985) the soil is considered low permeable.  The experimental field has been carried out in the farm of Agricultural Research Station, which belongs to Agriculture Research Centre. The area is situated at the end of El-Dakhlia Governorate between two main drains, El-Serw drain and El-Harana drain, which they are, meets at a city called El-Alexandria El-Gadeidh. The two drains end in El-Serw pumping drainage station, which lifts the drainage water to El-Manzala Lake.  The area of the field under study is representative of northern low lands, fluvio-marine clay salt affected soils of low productivity. Moreover, they are assumed to lie in the zone of hydrostatic pressure. A main controversial factor is the extreme salinity of the groundwater table.

The main treatments are subsurface drainage. The 3 D  drainage system was  installed four years ago. And  are 100-m. length and 150 cm. depths at the 3 D pipe  end. The collector line is 60 m. long and its outlet (2.5-m. depth) is in the main drain  The experimental field was designed with three drain spacing treatments separated by buffer zones (Dielman and Trafford, 1976): (i) 15 m. spacing (calculated spacing according to the steady state formula, (Houghoudt, 1940)); (ii) 30 m. spacing (conventional spacing adopted in the surrounding areas); and (iii) 60 m. spacing (double of the conventional spacing for future secondary drainage treatments). The sub-treatments are two types of subsoiling; the distance between plowing two metre and the depth is 50 cm. There are: (i) One direction: Parallel orientation subsoiling type and perpendicular on 3D  drains, and (ii). Two directions: Net structure subsoiling type. Initial state soil samples were collected from each treatment and after crop harvest. The soil profiles were dug out at the middle between two drains up the depth of 150 cm. The soil samples were collected every 30 cm. All samples were air dried and kept for soil chemical analysis.  Undisturbed soil samples were taken using cores with diameter of 4.3 cm and height of 3.0 cm. Bulk density was determined using core method at field moisture condition (Vomocil, 1957). Air-dried soil sample was gently crushed and sieved through a 2 mm sieve. 
Electrical conductivity “EC”, soluble cations and anions were measured in soil solution extract (1:5) according to Black, 1965. Exchangeable sodium and potassium were determined using ammonium chloride (Jackson, 1973). All the data collected were subjected to the statistical analysis using statistical computer program.