负压渗管对土壤盐分淋洗效果影响的模拟研究

Numerical analysis of soil salt leaching influenced by subsurface seepage pipe with negative pressure

【目的】探究土壤淋洗过程中负压多孔渗管的出流机制及其对土壤水盐运移的影响特征。【方法】采用HYDRUS模型对埋设真空负压渗管的土壤剖面进行数值建模,模拟淋洗过程中不同土壤质地(粉质黏土、黏土、黏壤土、砂质黏壤土、砂壤土)、土表入渗水头(2、4、6、8、10cm)和渗管内负压水头(200、500、1000、1500、2000cm)组合情景下土壤水盐动态形式,并分析淋洗前后土壤脱盐率以及单位灌水对应的渗管排盐量。【结果】(1)负压渗管的排水主要源于下渗水在土壤剖面内形成的悬着水带,当悬着水带含水率达到饱和时排水通量达到最大。(2)负压渗管下土壤质地对负压渗管的排水排盐效果起决定作用,砂粒占比越高对应的脱盐效率和淋洗效率越高。(3)各处理的脱盐率与入渗水头和管内负压均呈微弱的正相关,但在砂质黏壤土和砂壤土中,增大入渗水头将降低淋洗效率。(4)负压渗管相对无渗管的脱盐率最大提升程度为7.91%,但提升程度从渗管上方向两侧递减,并在渗管下方存在随管内负压减小而范围扩大的积盐区。【结论】淋洗过程中负压渗管在偏砂性的土壤中模拟所得水盐的调控能力较强,能够在淋洗水量不变的条件下提升土壤的局部脱盐收益。

【Objective】Subsurface seepage pipe assisted with vacuum negative pressure is an emerging technology aimed at regulating soils water dynamics.In this paper,we examine the effects of negative-pressure seepage pipe(NPSP)on soil salt leaching.【Method】We used the HYDRUS model to simulate salt leaching in soils with five soil textures:silty clay,clay,clay loam,sandy clay loam,and sandy loam.Five infiltration water heads(2,4,6,8 and 10 cm)and five negative pressure heads(200,500,1000,1500 and 2000 cm)in the subsurface pipes were considered in the simulations.Based on the simulated results,we calculated the changes in soil salt content before and after a leaching event,as well as the salt leaching efficiency(salt leached per unit of irrigation water).【Result】①Water discharged by the NPSP was primarily originated from the wetting zone in soil profile formed during the infiltration process,and the maximum pipe discharge was obtained as the wetting zone was saturated.②Soil texture was a key factor in influencing water and salt discharge,with both the desalination rate and salt leaching efficiency increasing as sand content increased.③For all the tested soil textures,the desalination rate was positively correlated with both the surface infiltration head and the inner-pipe negative pressure.However,for sandy clay loam and sandy loam soils,increasing the infiltration head lead to a lower salt leaching efficiency.④As compared with no-pipe control,the maximum increase of the desalination rate under the application of NPSP was 7.91%,while increased desalination rate were obtained in the soil profile above the NPSP,and the values decreasing with the lateral distance away from the NPSP;There was a salt accumulation zone directly below the NPSP,and its region expanded with the decrease of the applied negative pressure.【Conclusion】NPSP is feasible to facilitate soil desalination without increase the water consumption for leaching practice,and the desalination performance of NPSP is likely be improved in field with sandy soil.