Effect of salinity, sodium adsorption ratio and depth of water table on soil salinization under cropping and fallowing conditions

摘要

The effect of salinity, sodium adsorption ratio and depth of water table on soil salinization under cropping and fallowing conditions was investigated. Wire and wooden columns were constructed and lined with clear water-tight plastic sheets to hold the soil. A sheet of plastic screen was bound with a string on the lower end. The dimensions of soil columns, 30 x 30 x 50 cm and 3 x 30 x 75 cm, were chosen in the investigation. The lower ends of the soil columns were placed in wooden basins lined with plastic sheets to prevent water loss to the ground. To prevent evaporation, the groundwater system was covered with a plastic sheet. The whole experiment was covered by a plastic sheet about 4.5 meters in height to prevent penetration of rainfall;The four treatments, consisting of cropping and fallowing, varying concentrations of salt (CaCl(,2) + NaCl) and sodium adsorption ratio in the ground at varying groundwater depths, were (1) 0.23% salt (SAR = 25) and soil depth 50 cm, (2) 0.23% salt (SAR = 25) and soil depth 75 cm, (3) 0.684% salt (SAR = 11) and soil depth 50 cm, and (4) 0.684% salt (SAR - 11) and soil depth 75 cm;The crop consisted of 50 plants per soil column of sudangrass and equal amounts of distilled water were applied to the surface of all soil columns at irregular intervals, beginning at an early stage of plant growth until the depth of roots reached the advance wetting of capillary rise from groundwater and then stopped. The constant groundwater level was maintained by adding increments of salt solution when it was reached;After sudangrass was harvested two times (144 days), the average water loss from the soil and accumulation of soluble salts on the surface of soils were favored by salt concentration in groundwater, depth of groundwater and the existence of crop;The upward movement of sodium is different than the movement of calcium. The calcium precipitates and increases on the soil surface but the sodium increases near the groundwater table.