积水入渗下不同矿化度水对红壤水盐运移特征的影响

The Effects of Concentration of Ponding-Infiltration Water on Water and Salt Movement in Soils

【目的】探讨积水入渗条件下矿化度对酸性红壤水盐运移特征的影响,为我国南方非常规水合理利用提供参考。【方法】采取土柱入渗试验,以蒸馏水灌溉(CK)为对照,探究不同矿化度水(1、2、3、5、10 g/L)入渗下南方红壤水分动态运移、水盐分布及土壤pH值变化,并量化矿化度与入渗模型参数关系。【结果】与CK相比,1~10g/L处理抑制红壤水分入渗,同一时刻累积入渗量表现为CK>1 g/L处理>5 g/L处理>2 g/L处理>3 g/L处理>10 g/L处理。5 g/L处理持水能力显著高于其他处理(p<0.05),单位时间湿润锋运移距离小于CK和1、2 g/L处理。Kostiakov公式较Philip方程能更精确描述1~3 g/L处理红壤累积入渗量随时间变化,矿化度大于3 g/L时则相反。红壤累积入渗量与湿润锋运移距离符合线性关系,红壤持水能力、入渗模型参数与矿化度关系均满足三次多项式(R2>0.95,RMSE<0.06)。1~5 g/L处理可使5~25 cm土壤平均含水率增加0.09%~4.61%,各处理土壤EC值和Na^(+)、Cl^(-)质量分数随深度增加呈减小趋势,矿化度对25~40cm范围土壤盐分的影响小于上层土壤。与CK相比,1~5g/L处理加剧红壤酸化,10 g/L处理则增加土壤pH值。【结论】矿化度对土壤酸化和分散作用程度不同是造成红壤水盐运移特征差异的原因,南方红壤区非常规水安全利用需综合考虑矿化度作用下土壤水盐、酸碱环境变化。

【Background】Seasonal water shortage in southern China has made water supply unable to meet the demand and using unconventional water as a supplementary resource for irrigation can partly relieve this pressure.The widely distributed red soils in southern China are weakly acidic characterized by low porosity,and to what extent irrigating such soils with salt-rich unconventional water affects their transport properties is poorly understood.【Objective】This paper is to fill this gap by systematically studying the effect of irrigation water salinity on water flow and solute movement in the red soil aimed to improve unconventional water irrigation management in these regions.【Method】The experiment was conducted in repacked columns with distilled-water irrigation taken as control(CK);the concentration of the irrigation water ranged from 1.0 to 10 g/L.In each treatment,we measured spatial distribution of water and salt in the soil profile,as well as pH at the end of infiltration.【Result】Compared with CK,saline water irrigation impeded water infiltration,with the impedance increasing with salinity concentration.Water-holding capacity of the soil did not show noticeable change when the salinity was less than 3 g/L,but increased significantly when the salinity was 5 g/L(p<0.05).Water infiltrating rate decreased as time elapsed,and 160 min after inception of the infiltration,the advancing speed of saline water front became slower than that of freshwater.Both Kostiakov and Philip formulate can accurately describe the change of cumulative infiltration with time,with the former working better when salinity was less than 3 g/L and the latter more accurate in other treatments.The cumulative infiltration linearly increased with the advancing distance of the wetting front,while the water-holding capacity and infiltration parameters varied with salinity in a way that could be described by a cubic polynomial function with R2>0.95 and RMSE<0.06.Irrigating with saline water in the range of 1~5 g/L increased water content in the 5~25 cm of soil by 0.09%~4.61%.It was found that EC,Na^(+)and Cl^(-) content decreased with soil depth,and that the effect of irrigation water salinity on soil salinity was more significant in the top 0~25 cm soil than in the subsoil.Compared with CK,irrigating with water at salinity 1~5 g/L acidified soil,while when the water salinity increased to 10 g/L it alkalized the soil.【Conclusion】Irrigation water salinity not only modulates water flow and solute movement in the red soil but also affects its physical properties.Our results showed that irrigating the red soil with unconventional water in southern China should consider the consequences for water and salt redistribution,as well as soil acidification or alkalinization.