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| DOI：10.13522/j.cnki.ggps.2026124 |
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| Effects of alternating irrigation with NaCl solution and freshwater on hydraulic properties and pore structure of red soils |
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Wang Hui, Hu Bo, Kong Qianqian
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1. College of Water Resources & Civil Engineering, Hunan Agricultural University, Changsha 410128, China;
2. Engineering Research Center of Precision Irrigation Control for Irrigation Districts in Hunan, Changsha 410128, China
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| Abstract: |
| 【Objective】Red soils are widely distributed in subtropical regions and are characterized by strong weathering, low fertility and sensitivity to changes in soil structure and hydraulic properties. The increasing use of reclaimed water for irrigation on red soils raises concerns over the potential effects of dissolved solutes, particularly Na+, on their pore structure and water transport properties. The objective of this study was to investigate changes in the hydraulic properties and pore structure of red soil under alternating infiltration with freshwater and NaCl solutions used to represent the effect of Na+ as a typical solute in reclaimed water. 【Method】A one-dimensional horizontal infiltration experiment was conducted using a typical red soil packed to a bulk density of 1.30 g/cm3, with tap water as the control (CK). Two sets of single-factor treatments were established: NaCl concentrations of 1, 3, 5, and 10 g/L at one alternation cycle, and alternation frequencies of 1, 2, 4, and 6 cycles at a fixed NaCl concentration of 3 g/L. Soil water and salt distributions, water-retention and hydraulic-conductivity characteristics, and equivalent pore-size distribution were determined.【Result】①Soil hydraulic properties responded nonmonotonically to NaCl concentration, with a transition occurring between 3 and 5 g/L. At 1 and 3 g/L, the proportion of macropores increased and water-retention capacity decreased, while unsaturated hydraulic conductivity and soil-water diffusivity were 15%-25% higher than those of CK. At 5 and 10 g/L, the proportion of micropores increased. At 10 g/L, field capacity was 12.67% higher and hydraulic conductivity was 20%-30% lower than those of CK. ②Increasing alternation frequency increased the proportion of macropores while reducing water-retention capacity. At six alternation cycles, compared with CK, the proportion of macropores increased by 116.63%, gravitational water content increased by 115.63%, and field capacity decreased by 16.82%. ③When NaCl concentration was 10 g/L, alternating irrigation decreased the van Genuchten parameter α by 53.6% relative to CK, indicating a decrease in characteristic pore size. When alternation frequency was 6 cycles, alternating irrigation increased the parameter α by 221.4% relative to CK, indicating an increase in characteristic pore size. 【Conclusion】The hydraulic response of red soil under alternating infiltration showed a NaCl concentration threshold and cumulative deterioration as alternation frequency increased. Increasing alternation frequency promoted macropore development but facilitated water leaching, indicating a deterioration in soil water-retention capacity. To mitigate the risk of soil structural degradation and excessive water leaching, under the conditions of this experiment, the NaCl solution concentration should be maintained below 3 g/L and the alternation frequency should be strictly limited; field validation is required before applying this recommendation to reclaimed-water irrigation. |
| Key words: red soil hydraulic characteristics pore size distribution alternating infiltration reclaimed water |
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