干旱地区排盐暗管优化布局关键参数研究

为探究干旱地区暗管配合淋洗的排盐效果及关键影响因素,该研究在新疆焉耆盆地布置了暗管排盐试验,研究淋洗前后土壤剖面的水盐变化规律和不同淋洗定额下相同暗管布局的暗管排水排盐量差异,结合正交试验分析方法研究暗管布局参数中影响土壤脱盐率的显著因素,并分析淋洗定额与暗管布局参数对土壤脱盐率的交互影响。结果表明:1)暗管排水后,土壤剖面含水率明显增大,表层平均含水率由0.20增加为0.30cm~3/cm~3,含盐量不同程度减小,表层平均盐量由10减少为5g/kg;2)暗管排水流量呈现先迅速增大,后缓慢减小的规律,而暗管排水电导率则在排水过程中无明显变化,且淋洗定额越大,暗管排水排盐量越大;3)暗管间距和埋深是影响脱盐率的显著因素(P分别小于0.05和0.01),而管径则对脱盐率无显著性影响;淋洗定额越大,土壤脱盐率越大,且在较大淋洗定额差异条件下,淋洗定额和暗管布局参数对土壤脱盐率无交互影响。研究结果表明,对于干旱地区暗管排盐工程布置,合适的埋深和间距很重要,淋洗定额也是影响脱盐效果的关键因素。考虑节约水资源和节省工程造价,研究区合适暗管埋深为1.4 m,间距为8 m,管径为90mm,此时采用300mm的淋洗定额进行冬灌,即可以满足36%的目标脱盐率。研究结果可以为干旱地区暗管合理布局选择提供依据。

Key parameters for the optimal layout of subsurface drainage pipe in arid areas

Abstract: Subsurface drainage has widely been constructed to discharge water and control the groundwater level against soil salinization in most arid regions. The main purpose of subsurface pipe is to discharge the salt from the soil profile under spring or winter irrigation. Thus, the appropriate layout parameters of subsurface drainage in arid and semi-arid areas can be different from humid regions. Therefore, it is highly necessary to investigate the influence factors of soil desalinization and salt discharge under subsurface drainage pipes in arid regions. In this study, there were four objectives: 1) to investigate the change of soil water content and salinity under subsurface drainage pipes with different layouts and irrigation quota; 2) to explore the time-varying process of flow flux and electrical conductivity under subsurface drainage pipes in each treatment, and thereby to determine the water and salt discharge amount of subsurface pipes with different layout and irrigation quota; 3) to analyze the influencing factors of desalinization rate in subsurface layout parameters; 4) to clarify the interaction of irrigation quota and layout parameters of subsurface pipes on the soil desalinization rate. Taking the Yanqi County, Xinjiang Uygur Autonomous Region of China as a study area, the field experiments were conducted in 2018 and 2020, where the irrigation quota was 490 mm for 2018, and 288 mm for 2020. Three layout parameters of subsurface pipes with every three levels were considered in the experiment, including three spacing (6, 10, and 20 m), three drain depths (0.8, 1.1, and 1.4 m), and three pipe diameters (90, 110, and 160 mm). An orthogonal experimental design was adopted to combine each parameter and level, where there were nine treatments in total. Multi-factors analysis of variance was made to clarify the significant influencing factors on the desalinization rate. The results show that the water content of the soil profile increased obviously before and after the experiment, whereas, the soil salinity relatively decreased under subsurface drainage. The duration of subsurface drainage ranged from 245 to 441 h during discharge. The flow flux of subsurface pipes increased rapidly at first, and then decreased slowly, whereas, the electrical conductivity was relatively stable, where the average electrical conductivity of drainage water was 12.65 mS/cm, related mainly to the salinity of soil profile. The accumulative amount of water and salt discharged from the subsurface pipe decreased significantly, with the decrease of irrigation quota. The soil desalinization rate presented a significant relationship with the subsurface pipe spacing and depth (P< 0.05 and 0.01, respectively) under the same irrigation quota. Specifically, it was negatively correlated with the spacing, but positively correlated with the buried depth, whereas, there was no significant relationship with the pipe diameter. The relationship between the desalination rate of soil above 80 cm (R) with the drainage spacing (L), the buried depth (D), and the irrigation quota (I) was represented as N=-0.8L+28D+58I-14, in the study area. Consequently, an optimal drainage depth and spacing are very necessary for the high efficiency of the subsurface drainage system in arid areas. In addition, the leaching quota is also the key factor affecting the desalinization rate. The buried depth of the subsurface drainage pipe is recommended as 1.4 m, and the drain spacing is 8 m, while the diameter is 90 mm for the study region, considering water-saving and engineering costs. In this case, the leaching quota of 300 mm can meet the national requirements of desalinization. This finding can provide a promising basis to choose appropriate parameters of subsurface pipe layout and irrigation quota in arid areas.