南方丘陵区多层土壤结构水平和垂向渗流特征试验与模拟研究

南方丘陵地区地形起伏,上下游田块及田块内部不同层之间土壤质地差异较大,存在复杂的水分转化关系。为揭示该地区田块内多层土壤水分运动规律,在湖北省漳河水库灌区团林灌溉试验站,开展田块变化水层条件下水分通过犁底层垂直入渗以及通过耕作层侧向入渗试验,观测土壤累积入渗量及各层含水率的变化过程;建立基于HYDRUS-2D的土壤水分二维渗流模拟模型。经验证,模型模拟值和田间实测值基本吻合;试验发现由于土壤性质差异,田块犁底层的存在会抑制水流的垂直运动,减少深层渗漏,但同时增强了水流沿耕作层侧向运动的能力。试验期间,水分沿犁底层平均垂向入渗速率为0.094 cm/min,沿耕作层平均侧向入渗速率为0.138 cm/min;入渗稳定后,渗漏水量占田面累积入渗量的21.11%,其中垂直渗漏水量占0.46%,侧向渗漏水量占20.65%,耕作层侧向渗漏水量占侧向渗漏水量的81.06%。结果表明,土壤侧向渗漏对水量损失的贡献较大,控制田块渗漏特别是耕作层侧向渗漏对南方地区节水减排具有十分重要作用。

Field experiment and simulation of lateral and vertical water flow in multi-layer soil in hilly region of southern China

With undulating conditions in hilly region of southern China, the mechanism of soil water trans-formation is complicated due to different soil textures between upstream and downstream fields as well as different layers within field. In order to reveal the influence of field different layers on soil water move-ment, field experiment was conducted in Tuanlin experimental irrigation station of Zhanghe irrigation dis-trict in Hubei province. Both water lateral infiltration through the cultivated horizon layer(CHL) and verti-cal infiltration through plow pan layer(PPL) under variable water table in field were monitored or estimated in the experiment. The processes were also simulated by a two-dimensional soil water movement model un-der variable water head using HYDRUS-2D, which show that the simulated results agree well with ob-served values. The results demonstrate that the PPL with compact structure in field,decreased deep percola-tion by retarding water vertical movement, but at the same time enhanced water lateral movement through the CHL. The average soil stable vertical infiltration rate through the PPL was 0.006cm/min,while the aver-age soil stable lateral infiltration rate through the CHL was 0.05cm/min. Based on the analysis of soil water balance at the stage of steadily infiltration, the total percolation in experiment area accounted for 21.11% of the cumulative infiltration, 0.46% and 20.65% of which were attributed to the vertical percolation and lateral seepage, respectively, and the CHL contributed 81.06% to the lateral seepage. The study illustrates that the lateral seepage plays an important role in water losses so that it is very essential to control percola-tion especially lateral seepage for water-saving and drainage reduction in southern China.