Abstract
Salinity is a major threat to the sustainability of irrigated agriculture in arid and semi-arid regions. Leaching is the primary measure for removing excess salts from the root zone, but not all water applied to the soil surface contributes to the removal of salts. In clayey soils, bypass flow along cracks can occur without being mixed with saline pore water in the matrix. To present a field dataset to quantitatively evaluate the contribution of bypass flow to the leaching of salts, soil sampling and monitoring of groundwater and discharge from a tile drain were carried out in farmland having a cracking soil in the Nile Delta. The electrical conductivities of 1:2 extracts were measured to evaluate the salinity of the soil. The first evidence for the occurrence of significant bypass flow through cracks was the salinity of the pore water, which was nearly triple that of the shallow groundwater and outflow from drainage. Second, the difference in root zone salinity before and after paddy rice cultivation was not significant. Third, the gradient of the groundwater table was very small. in spite of the low saturated hydraulic conductivity. Fourth, the salinity of the outflow from the tile drain dropped just after irrigation or rain. These results indicated that bypass flow through cracks played a significant role in the drainage process in the soil, and that nearly half of the water bypasses through cracks in the field with a cracking soil.
Highlights
Salinity is a major threat to the sustainability of irrigated agriculture in arid and semi-arid regions
The objective of this study was, to present field dataset in the Nile Delta toinquantitatively evaluate the contribution of bypass flow in the leaching the Nile Delta to quantitatively evaluate the contribution of bypass flow in the leaching of salts
All the results presented above\ clearly indicate that bypass flow played a significant role
Summary
Salinity is a major threat to the sustainability of irrigated agriculture in arid and semi-arid regions. The salinity of the outflow from the tile drain dropped just after irrigation or rain These results indicated that bypass flow through cracks played a significant role in the drainage process in the soil, and that nearly half of the water bypasses through cracks in the field with a cracking soil. To remove excess salts from the root zone to mitigate the salinity hazard, more water than that required to meet crop evapotranspiration is periodically applied [3] Such an intentional “over-irrigation” is called leaching, which has been the primary measure and widely practiced for salinity control. Oster et al [6] compared three methods of leaching: continuous ponding, intermittent ponding, and sprinkler, and noted that the lower leaching efficiency of continuous ponding is attributable to bypass flow in cracks and macropores. Moreno et al [7] reported a 10 times larger apparent with cracks than a matrix in [7]
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