土壤盐结皮人工培育及其破损程度对土壤蒸发的影响

Artificial cultivation of soil salt crust and effects of its damage rate on soil evaporation

土壤盐结皮在干旱半干旱区广泛发育,对地表土壤水文过程具有重要影响,而外力对盐结皮的机械破损干扰现象普遍存在。该文以塔克拉玛干沙漠流动风沙土为例,通过室内试验利用不同矿化度(5、10、20和30 g/L)的不同盐溶液(NaCl、Na2SO4、CaCl2、KCl)模拟咸水灌溉下盐结皮的形成发育过程,根据盐结皮理化性质确定了其最适人工培育条件,并在此基础上模拟了盐结皮不同破损程度(破损100%、破损50%、破损25%和无破损)影响下的土壤蒸发过程。结果表明:盐结皮的硬度、抗剪切力、pH值和电导率通常随着灌溉水矿化度的增加而增大,采用30g/LNaCl溶液培养盐结皮厚度和硬度均较大;土壤日蒸发量随盐结皮破损程度的增加而增加,并随灌水天数呈递减趋势;土壤累积蒸发量随灌水天数以及破损程度的增加而增大,盐结皮破损100%的土壤日蒸发量和累积蒸发量与其他各处理之间有显著性差异;盐结皮对土壤蒸发的累积蒸发抑制效率随灌水时间的延长呈递增趋势,随破损程度的增加而降低,盐结皮无破损处理的累积蒸发抑制效率最高达58.84%,而破损50%的处理最大仅为30.20%。总之,土壤盐结皮的人工培育在方法上是可行的,其对土壤水分蒸发具有明显的抑制作用,且其破损程度对蒸发过程具有显著影响。这对于揭示干旱半干旱区盐渍土壤水文过程和指导水土资源的合理利用具有重要意义。

Soil salt crust is widely developed in arid and semi-arid areas, which has great impacts on earth surface soil hydrological processes, and interference of external forces on mechanical damage of salt crust is common. Shifting aeolian sandy soil in the Taklimakan Desert was taken as an example, different salt solutions (NaCl, Na2SO4, CaCl2, KCl) of different salinities (5, 10, 20, 30 g/L) were used to simulate the formation and development of salt crust under saline water irrigation. The air temperature and humidity during the salt crust cultivation were recorded. The optimum artificial cultivation conditions were determined based on the physiochemical properties analysis results of salt crust. Furthermore, the soil evaporation process under the influence of different damage degree of salt crust (damage rates of 100%, 50%, 25% and 0) was monitored. The results showed that the hardness, shear resistance, pH and EC of the salt crust generally increased with the increasing salinity of irrigation water. The thickness and hardness of the crust were the largest for 30 g/L NaCl solution, and its hardness was 24.17 kg/cm^2, shear resistance was 6.73 kg/cm^2, pH value was 7.45, and EC was 3.77 mS/cm. Daily soil evaporation in micro-lysimeters (MLS) increased with the increasing damage degree of salt crust and decreased with the days after irrigation. Soil accumulative evaporation increased with the days after irrigation and the degree of damage. During the soil moisture evaporation, soluble salts gradually crystallized on the soil surface, which not only blocked soil capillary action, but also inhibited diffusion of water vapor into the atmosphere. Meanwhile, it changed and lowered surface soil temperature, thus further reduced soil evaporation. Thus, the evaporation rate of water gradually slowed down and the amount of evaporation per day reduced. Daily evaporation and cumulative evaporation with 100% soil salt crust were significantly different from the other treatments. Cumulative evaporation inhibition efficiency of salt crust on soil evaporation increased with the increasing time after irrigation, and decreased with the increasing damage degree, which indicated that soil cumulative evaporation would change due to the change of salt crust damage. The cover of salt crust had positive effect on maintaining high soil moisture and plant growth in arid regions. Cumulative evaporation inhibition efficiency of salt crust increased with the days after irrigation, and decreased with the increasing damage rate. When the crust was damaged by 50% or 0, the cumulative evaporation inhibition efficiency reached the maximum on the 7^th day. When the crust damage rate was 25%, the maximum evaporation inhibition efficiency was on the 4^th day.The maximum cumulative evaporation inhibition efficiency of salt crust without damage was 58.84%, while it was only 30.20% under damaged rate of 50%. In summary, soil salt crust could be artificially cultivated, and it has obvious inhibitory effects on soil evaporation, and its damage degree has significant impacts on soil evaporation process. It is of great significance to reveal the hydrological processes of saline soils and to guide the rational utilization of soil and water resources in arid and semi-arid areas.