盐阳离子类型对红壤裂缝开闭规律的影响

Effects of salt cation types on propagation and closure law of desiccation cracks in red soil

为了探究灌溉水中盐离子浓度及类型对土壤裂缝变化过程的影响,为南方灌溉用水安全提供数据理论支持,采用蒸馏水配置15.0,10.0,5.0和2.5 g/L等4个质量浓度梯度的NaCl,KCl,CaCl2和MgCl2等4种类型溶液,分别浸泡南方亚热带地区的典型红壤,并且采用恒温蒸发模拟干燥过程和喷湿法模拟增湿过程,结合数字图像技术提取土壤表层开裂闭合过程中裂缝主要几何参数,分析盐阳离子类型对红壤裂缝发育过程特征的影响.结果表明:红壤干燥过程中,裂缝在土壤质量含水率由30%降至10%时增长最快;在质量含水率低于10%后达到最大值并保持稳定不变.红壤的裂缝面积密度与4种盐阳离子浓度呈极显著正相关关系,裂缝长度密度与K+及Mg2+呈极显著负相关,与Ca2+呈显著负相关关系.4种盐阳离子对红壤开裂面积促进程度深浅顺序为Na+,K+,Ca2+,Mg2+;4种不同离子浓度的处理中,NaCl质量浓度为10.0 g/L,而KCl,CaCl2和MgCl2质量浓度为15.0 g/L的溶液对红壤开裂促进效果最好,其裂缝面积相比于蒸馏水处理分别增大了155.0%,160.1%,109.4%和39.2%.红壤的开裂含水率低于闭合含水率,4种盐阳离子浸泡后会使红壤的开裂含水率和闭合含水率均升高.

In order to investigate the influences of salt ion concentration and its type in irrigation water on the process of soil crack change and to provide data theory for the safety of irrigation water in south China,the south subtropical typical red soil was soaked by using four solutions of NaCl,KCl,CaCl2 and MgCl2 with the solute concentration of 15.0 g/L,10.0 g/L,5.0 g/L and 2.5 g/L,respectively.The dry and wet processes were simulated by using isothermal evaporation and water spraying,respectively.In order to analyze the development of red soil fracture affected by salt cation type,the geometric parameters of soil crack were extracted by using digital image technology.The results showed that the cracks in the drying process of red soil increased most rapidly with the moisture content decreased from 30%to 10%,and reached the maximum when the soil mass moisture content was lower than 10%,and then remained stable.The crack area density of red soil was significantly positively correlated with the concentration of four salt cation.The crack length density was significantly negatively correlated with K+and Mg2+,and significantly negatively correlated with Ca2+.The order of the positive effect of four ions on the cracking area of red soil was Na+>K+>Ca2+>Mg2+.Compared with distilled water treatment,10.0 g/L of NaCl and 15.0 g/L of KCl,CaCl2 and MgCl2 had large effect on the cracks in the red soil,which increased by 155.0%,160.1%,109.4%and 39.2%,respectively.The cracked water content was lower than the closed water content.Moreover,the cracked and closed water contents of red soil increased after soaking with four kinds of salt cation solutions.